nanoall - Nanotechnology Blog

Glass nano metal matrix

2012-01-25T23:44:00.000-08:00

Nanoparticles of metals and semiconductors in glass matrix are commonly formed by homogeneous nucleation in solid state. 'First the desired metal or semiconductor precursors are introduced and homogeneously distributed in the liquid glass melt at high temperatures during glass making, before quenching to room temperature. Then the glass is annealed by heating to a temperature to about the glass transition point and then held for a pre-designed period of time. During annealing, metal or semiconductor precursors are converted to metals and semiconductors. As a result, supersaturated metals or semiconductors form nanoparticles through nucleation and subsequent growth via solid-state diffusion.

Homogeneous glasses are made by dissolving metals, in the form of ions, in the glass melts and then rapidly cooled to room temperature. In such glasses metals remain as ions. Upon reheating to an intermediate temperature, metallic ions are reduced to metallic atoms by certain reduction agents such as antimony oxide which is also added into the glass. Metallic nanoparticles can also be nucleated by ultraviolet, X-ray, or gamma-ray radiation if a radiation-sensitive ion such as cerium is present. The subsequent growth of the nuclei takes place by solid-state diffusion. For example, glasses with nanoparticles of gold, silver, and copper can be prepared with such an approach. Although metallic ions may be highly soluble in the glass melts or glasses, metallic atoms are not soluble in glasses. When heated to elevated temperatures, metallic atoms diffuse and migrate through the glasses and subsequently form nuclei. These nuclei grow further to form nanoparticles of various sizes. Since solid-state diffusion is relatively slow, it is relatively easy to have a diffusion-controlled growth for the formation of monosized particles.
Nanoparticles dispersed in glass matrix can be synthesized through sol-gel processing as well. There are two approaches: (i) mixing presynthesized colloidal dispersion with matrix sol before gelation, and (ii) making a homogeneous sol containing desired ions for the formation of nanoparticles first and annealing the solid product at elevated temperatures.

Synthesis of metallic nanoparticles

2012-01-21T06:51:00.000-08:00

Metallic nanoparticles
The term metal nanoparticle is used to describe nano sized metals with dimensions (length, width or thickness) within the size range 1‐100 nm. Metallic nanoparticles display properties that are quite different from those of individual atoms, surfaces or bulk materials. The main characteristics of MNPs are large surface‐area‐to‐volume ratio as compared to the bulk equivalents, large surface energies, existence as a transition between molecular and metallic states providing specific electronic structure (local density of states LDOS), have plasmon excitation, quantum confinement, short range ordering, increased number of kinks, contain a large number of low‐coordination sites such as corners and edges, having a large number of ˝dangling bonds˝ and consequently specific and chemical properties and the ability to store excess electrons.
Their potential applications include, for example, use in biochemistry, in catalysis and as chemical and biological sensors, as systems for nanoelectronics and nanostructured magnetism.
Synthesis
Chemical methods Include chemical reduction of metal salts, alcohol reduction process, polyol process, microemulsions, thermal decomposition of metal salts and electrochemical synthesis. Physical methods include exploding wire technique, Plasma, chemical vapour deposition, microwave irradiation, pulsed laser ablation, supercritical fluids, sonochemical reduction and gamma radiation.
Reduction of metal complexes in dilute solutions is the general method of synthesis of metal colloidal dispersions, and a variety of methods have been developed to initiate and control the reduction reactions. In most cases the formation of monosized metallic nanoparticles is achieved by a combination of a low concentration of solute and polymeric monolayer adhering onto the growth surfaces. Both a low concentration and a polymeric monolayer can hinder the diffusion of growth species from the surrounding solution to the growth surfaces and the diffusion process is likely to be the rate limiting step of subsequent growth of initial nuclei, resulting in the formation of uniformly sized nanoparticles.
Precursors and reagents
In the synthesis of metallic nanoparticles, or more specifically, metallic colloidal dispersion, various types of precursors, reduction reagents, other chemicals, and methods are used to promote or control the reduction reactions, the initial nucleation and the subsequent growth of initial nuclei. The precursors include: elemental metals, inorganic salts and metal complexes, such as, Ni, Co, HAuC14, H,PtCl,, RhC1, and PdCI2. Reduction reagents includes: sodium citrate, hydrogen peroxide, hydroxylamine hydrochloride, citric acid, carbon monoxide, phosphorus, hydrogen, formaldehyde, aqueous methanol, sodium carbonate and sodium hydroxide.
Other synthesis methods
Metallic nanoparticles can also be prepared by an electrochemical deposition method employing a simple electrochemical cell containing only a metal anode and a metal or glassy carbon cathode. The electrolyte consists of organic solutions of tetra alkyl ammonium halogenides, which also serve as stabilizers for the produced metal nanoparticles. Upon application of an electric field, the anode undergoes oxidative dissolution forming metal ions, which would migrate toward the cathode. The reduction of metal ions by ammonium ions leads to the nucleation and subsequent growth of metallic nanoparticles in the solution. With this method, nanoparticles of Pd, Ni and Co with diameters ranging from 1.4 to 4.8 nm can be produced.
Gold nanoparticles
Colloidal gold has been studied extensively for a long time. In 1857 Faraday published a comprehensive study on the preparation and properties of colloidal gold. A variety of methods have been developed for the synthesis of gold nanoparticles, and among them, sodium citrate reduction of chlorauric acid at 100°C was developed more than 50 years ago and remains the most commonly used method.
Silver nanoparticles
Various methods have been developed for the formation of silver nanoparticles. Synthesis of Ag nanoparticles can be achieved by the UV illumination of aqueous solutions containing AgC104, acetone, 2-propanol and various polymer stabilizers. UV illumination generates ketyl radicals via excitation of acetone and subsequent hydrogen atom abstraction from 2-propanol and the ketyl radical may further undergo protolytic dissociation reaction. Both the ketyl radical and radical anions react with and reduce silver ions to silver atoms.
The reactions have a low reaction rate and favor the production of monosized silver nanoparticles. With the presence of polyethyleneimine as polymer stabilizer, silver nanoparticles formed using the above photochemical reduction process have a mean size of 7nm with a narrow size distribution.
Although polymer stabilizers play a very important role in the synthesis of metal nanoparticles, they can be prepared without using any polymer stabilizer. Silver nanoparticles can be prepared using commercially available set of solutions. Without adding any stabilizing reagent, it can be synthesized using aqueous dispersion of silver nanoparticles of 20-30 nm in size. The dispersion is likely to be stabilized by electrostatic stabilization mechanism. However, the particle size is sensitively dependent on the synthesis temperature. A small variation of temperature would result in a significant change of diameters of metal nanoparticles.

Nanocross

2012-01-19T03:05:00.000-08:00

Metallic nanostructures
Metallic nanostructures excite electrons close to their surface upon incidence of light at a particular frequency. The collective movement of electrons, or resonance, in the metal converts the light energy into heat. The wavelength at which the resonance occurs is strongly dependent on the size and shape of the nanostructures.
Metallic nanocross
Nanocross is a unique cross-shaped nano structure having arms located at an angle. In metallic nanocross spectral tunability can be achieved by changing the cross arm length and the angle between the arms. The degree of rotational symmetry of the nanocross can be varied by adding extra arms, changing the arm angle and shifting the arm intersection point. The symmetry of the particles has a crucial influence on the plasmon coupling to incident radiation. Pronounced dipole, quadrupole, octupole and Fano resonances can be observed in individual cross structures. Furthermore, the nanocross geometry proves to be a useful building block for coherently coupled plasmonic dimers and trimers where the reduced symmetry results in hybridized sub radiant and super radiant modes and multiple Fano interferences.
Gold nanocross
Researchers at ASTAR Institute of materials and Engineering have developed gold plasmonic nanocrosses that are particularly suited to eliminating cancer cells in cancer therapy and used to kill human lung cancer cells.
Chemical synthesis of well-defined gold nanocrosses can be done through anisotropic growth along both 110 and 001 , whereas gold nanorods can be grown only along either 110 or 001 . The multiple branching is achieved by breaking the face-centered-cubic lattice symmetry of gold through copper-induced formation of single or double twins to result in gold nanocrosses.
The nanocrosses exhibit pronounced near-IR absorption with a great extension to the mid-IR region and get excited even when one of the branches is exposed to incident light. The unique cross-shaped gold structure enables multi-directional excitation to achieve a strong plasmonic resonance in the near- and mid-infrared region. This greatly lowers the laser power required for photo thermal cancer therapy compared to nanorods.
The gold nanocrosses useful as octopus antennas for capturing near-IR light for effective photo thermal destruction of cells, photo thermal destruction of super bugs on biofilms, two-photon luminescence imaging, IR sensing, thermal imaging and telecommunications.

Synthesis of oxide nanoparticles

2012-01-18T05:55:00.000-08:00

The application of nanoparticles in the processes of making commercial products has increased in recent years due to their unique physical and chemical properties. Few such commercially available nanoparticles are TiO2, ZnO and SiO2.

Fabrication of oxide nanoparticles
The most widespread route to fabrication of metal oxide nanoparticles involves the “bottom-up” approach involving the precipitation from aqueous solution from metal salts. Organo metallic species can also be used, but due to their cost and the difficulty in manipulating these compounds, they are used less frequently. An alternative “top-down” approach has been demonstrated for aluminum and iron oxide nanoparticles; however, it is possible that this methodology could be extended to other oxides.
Compared to the synthesis of metallic and non-oxide nanoparticles, the approaches used in the fabrication of oxide nanoparticles are less elaborate and there are less defined general strategies for the achievement of mono sized distribution. Although all the fundamental considerations, including a burst of homogeneous nucleation and diffusion controlled subsequent growth, are applicable to the oxide systems, the practical approaches vary noticeably from system to system. Reaction and growth in the formation of oxide nanoparticles are more difficult to manipulate, since oxides are generally more stable thermally and chemically than most semiconductors and metals. For example, Ostwald ripening is applied in the synthesis of oxide nanoparticles to reduce size distribution; the results may be less effective than in other materials. The most studied and best established example of oxide colloidal is silica colloids though various oxide nanoparticles have been studied. Commonly oxide particles in colloidal dispersions are synthesized by sol-gel processing. Sol-gel processing is also commonly used in the fabrication.
With increasing amount of commercial nanoparticles released into nature, their fate and effects on the ecosystem and human health are of growing concern.

Synthesis of nanomaterials

2012-01-17T09:08:00.000-08:00

Synthesis approaches
There are two approaches to the synthesis of nanomaterials and the fabrication of nanostructures: top-down and bottom-up. Attrition or milling is a typical top-down method in making nanoparticles, whereas the colloidal dispersion is a good example of bottom-up approach in the synthesis of nanoparticles. Lithography may be considered as a hybrid approach, since the growth of thin films is bottom-up whereas etching is top-down, while nanolithography and nano manipulation are commonly a bottom-up approach.
Both approaches play very important role in nanotechnology. There are advantages and disadvantages in both approaches. Among others, the biggest problem with top-down approach is the imperfection of the surface structure. It is well known that the conventional top-down techniques such as lithography can cause significant crystallographic damage to the processed and additional defects may be introduced even during the etching steps. For example, nanowires made by lithography are not smooth and may contain a lot of impurities and structural defects on surface. Such imperfections would have a significant impact on physical properties and surface chemistry of nanostructures and nanomaterials, since the surface over volume ratio in nanostructures and nanomaterials is very large. The surface imperfection would result in a reduced conductivity due to inelastic surface scattering, which in turn would lead to the generation of excessive heat and thus impose extra challenges to the device design and fabrication. Regardless of the surface imperfections and other defects that top-down approaches may introduce, they will continue to play an important role in the synthesis and fabrication of nanostructures and nanomaterials.
Bottom-up approach
Bottom-up approach is often emphasized in nanotechnology literature, though bottom-up is nothing new in materials synthesis. Typical material synthesis is to build atom by atom on a very large scale, and has been in industrial use for over a century. Examples include the production of salt and nitrate in chemical industry, the growth of single crystals and deposition of films in electronic industry. For most materials, there is no difference in physical properties of materials regardless of the synthesis routes, provided that chemical composition, crystallinity, and microstructure of the material in question are identical. Of course, different synthesis and processing approaches often result in appreciable differences in chemical composition, crystallinity, and microstructure of the material due to kinetic reasons. Consequently, the material exhibits different physical properties.
Bottom-up approach refers to the build-up of a material from the bottom: atom-by-atom, molecule-by-molecule, or cluster-by-cluster. In organic chemistry and/or polymer science, we know polymers are synthesized by connecting individual monomers together. In crystal growth, growth species, such as atoms, ions and molecules, after impinging onto the growth surface, assemble into crystal structure one after another.
Although the bottom-up approach is nothing new, it plays an important role in the fabrication and processing of nanostructures and nanomaterials. There are several reasons for this. When structures fall into a nanometer scale, there is little choice for a top-down approach. All the tools we have possessed are too big to deal with such tiny subjects. Bottom-up approach also promises a better chance to obtain nanostructures with less defects, more homogeneous chemical composition, and better short and long range ordering. This is because the bottom-up approach is driven mainly by the reduction of Gibbs free energy, so that nanostructures and nanomaterials such produced are in a state closer to a thermodynamic equilibrium state. On the contrary, top-down approach most likely introduces internal stress, in addition to surface defects and contaminations.

Synthesis of semiconductor nanoparticles

2012-01-14T03:52:00.000-08:00

Nonoxide semiconductor nanoparticles are commonly synthesized by pyrolysis of organometallic precursor(s) dissolved in anhydrate solvents at elevated temperatures in an airless environment in the presence of polymer stabilizer or capping material. In the synthesis of metallic nanoparticles, polymers attached on the surface are commonly termed as polymer stabilizers. However, in the synthesis of semiconductor nanoparticles, polymers on the surface are generally referred to as capping materials. Capping materials are linked to the surface of nanocrystallites via either covalent bonds or other bonds such as dative bonds. Examples are sulfur and transition metal ions and nitrogen lone pair of electrons form dative bond.
Semiconductor nanocrystallites
The formation of monodispersed semiconductor nanocrystallites is generally achieved by the following approaches. First, temporally discrete nucleation is attained by a rapid increase in the reagent concentrations upon injection, resulting in an abrupt supersaturation. Second, Ostwald ripening during aging at increased temperatures promotes the growth of large particles at the expense of small ones, narrowing the size distribution. Third, size selective precipitation is applied to further enhance the size uniformity. Although organic molecules are used to stabilize the colloidal dispersion, similar to that in the formation of metallic colloidal dispersions, the organic monolayers on the surfaces of semiconductor nanoparticles play a relatively less significant role as a diffusion barrier during the subsequent growth of initial nuclei. This is simply because there is a less extent or negligible subsequent growth of initial nuclei due to the depletion of growth species and the drop of temperature at the nucleation stage.
Researchers at Nanjing University have sonochemical methods for the preparation of nanoparticles with controllable morphologies. PbWO4 nanostructures with different morphologies, such as dendritic, flowery, and star-like, have been synthesized via a sonochemical route. It has been proved that the ultrasonic irradiation plays a crucial role in the morphology of the product. The researchers used a microemulsion system to successfully synthesize single-crystalline PbF2 nanorods via a sonochemical route.

Nano oxides

2012-01-14T03:39:00.000-08:00

Nano-oxides are essential materials in nanotechnology as their demand has greatly expanded. The materials are used in a variety of applications including colloid science, environmental remediation, catalysis and photo-catalysis, electronics, medicinal applications, separations, thin films, inks and disinfection. The efficient production of nanoparticles is likely to play a key role in the future of the chemical industry.
ZnO
ZnO, a wide-band gap semiconductor (3.37eV) at room temperature with a large exciton binding energy (60 meV), is a multifunctional material for a variety of practical applications due to its excellent physical and chemical properties. One-dimensional nanostructures of ZnO have attracted great interest because of their unique and fascinating optical, electrical, mechanical and piezoelectric properties together with their wide use in fundamental scientific research and potential technical applications, such as nano-ultraviolet lasers, piezoelectric devices, field emissions, gas sensors, dye-sensitized solar cells and photocatalyts.
Disinfectant property
Metal oxides like ZnO as well as sulphides like ZnS have efficient disinfectant rate due to increased surface to volume ratio which is an important property. In the presence of UV light the valence electrons in the nanoparticles are excited to form electron-hole pairs. These negative electrons and positive holes are strong oxidizers. When harmful substances like pesticides stick to the positive holes, they are disintegrated into harmless compounds. The excited electrons are also injected into bacteria in contact with nanoparticles and hence act as a disinfectant. This technology is used to decompose toxic pesticides, which take a long time to degrade under normal conditions.
Synthesis of ZnO
A simple and efficient route to synthesis ZnO nanowires at a low temperature is by thermal CVD. Thermal CVD of ZnO synthesis is usually viewed as cheap, low-toxic and efficient methods to fabricate various ZnO nanostructures with high crystal quality. Using these method ZnO nanowires can be quickly synthesized in 10 min without catalysts. The high crystal quality of synthesized nanowires show strong ultraviolet (UV) emission in their photoluminescence spectra.
Desert Nano-Roses of Nickel Oxides
Nano-scale nickel oxides and mixed-metal oxides can be fabricated using microwave irradiation in pure water into unique desert-rose-shaped nanostructures. These materials exhibit promising performance as nanocatalysts for CO oxidation and in energy storage devices.
Other oxides
Nanoparticles of ZrO2, TiO2, and CeO2 have been produced directly after the treatment of the suspension. Nanopowders of Y2O3 and La2O3 have been obtained after calcination of the hydroxide forms. Phosphor-based lanthanide nanomaterials can be used in a variety of quantum dot-type applications, and are particularly suitable for medical and pharmaceutical research. Nano Oxides, Carbonates and Hydroxides of Magnesium exhibit unique properties and can be used as a catalyst in electronics and ceramics, oil refining, in textile industry, for the synthesis of brand new, high-performance fire retarding agents and as an ideal material for the fabrication of industrial fabrics.

Nanoparticle solution to repair surface

2012-01-13T12:01:00.000-08:00

Researchers at the universities of Massachusetts and Pittsburgh in the US have developed a new technique to repair surfaces using oil-based microcapsules filled with a nanoparticle solution.
Nano capsules
Using a polymer surfactant that stabilizes oil droplets in water, the researchers encapsulated cadmium selenide nanoparticles in nano size thin wall capsules in such a way that the particles could be released when desired. The capsules roll or glide over damaged substrates and selectively deposit their nanoparticle contents into the damaged or cracked regions due to hydrophobic–hydrophobic interactions between a nanoparticle and the cracked surface. The nanoparticles can easily be tracked too because cadmium selenide is fluorescent.
Working
If nanoparticles were held in a certain type of microcapsule, they could probe a surface and release the nanoparticles into certain specific regions of damaged surfaces, where the defective regions possess characteristics that are very different to the undamaged one in terms of topography, wetting properties, roughness and chemical functionality. When applied the microcapsules glide over a surface and go into the cracks or imperfections that they encounter and release their nanoparticle cargo into them to repair them.
Applications
The technique has many practical applications in industry and research by avoiding the need to coat an entire surface when only a small fraction of it has been damaged. It could help massively to lower the amount of material required when repairing a damaged object or sample. It can also be used to detect damaged substrates by depositing sensor material into the regions of concern. It cam be used to repair a wide range of objects from aero plane wings to microelectronic components and biological implants.

Nano-ear

2012-01-13T11:33:00.000-08:00

Physicists in Germany have developed a "nano-ear" of detecting sound on microscopic length scales. The technique was discovered in the 1980s and is used routinely in research labs around the world. It is particularly useful for manipulating biological objects, since the optical field used to make the trap is non-destructive.

Working
The researchers suspended gold nanoparticles in a drop of water. They trapped one sphere in a laser beam and then fired rapid pulses of light from a second laser at others a few micrometres away. The pulses heated the nanoparticles, which disturbed the water around them, generating pressure, or sound, waves. The device can optically trap gold nanoparticle and could be used to "listen" to biological micro-organisms as well as investigate the motion and vibrations in tiny machines. When laser light is focused at a point in space gold nanoparticles can be trapped in optical tweezers and an electric dipole moment is induced in the particle and drawn to the most intense part of the laser's electric field. The particle inside an optical trap can also be used as an extremely sensitive and minuscule sound detector. The trapped particle can be made to move from its equilibrium position by vibrations from nearby sound waves whose frequency can then be calculated by analysing how much the particle has been displaced.
Set-up
The set-up consisted of two sound sources placed in a water-based medium. The first "loud" source is a tungsten needle glued on a loudspeaker that vibrates at a frequency of 300 Hz. The second, weaker source is made up of bunches of gold nanoparticles that are periodically heated by a second laser to create sound waves at a frequency of 20 Hz. The nano-ear is a 60 nm gold nanoparticle trapped in an 808 nm wavelength laser beam.
When either of the sound sources is turned on, the ensuing vibrations cause the trapped particle to move in the same direction as the propagating sound waves. The estimated sensitivity is six orders of magnitude below the threshold of human hearing.
Sound detector
The spectra reveal a clear, superimposed single peak at the frequency of the sound source. Further analysis reveals that the nano-ear can detect vibrations at a power level as low as –60 dB, which are six orders of magnitude lower than the threshold of a human ear.
Applications
The device could be used to analyze the sounds made by live micro-organisms, such as bacteria and viruses, to investigate artificial micro-objects that produce acoustic vibrations but that cannot be directly visualized in an optical microscope because of strong light absorption or scattering and to develop a new type of 'acoustic microscopy' because it is possible to bring very sensitive sound sensors in close vicinity to microscopic samples.

Gold NPs and its alloys

2012-01-09T10:33:00.000-08:00

Nanoparticles

Metal nanoparticles and alloy nanoparticles have remarkable optical, electronic and catalytic properties and have many different applications in biomedical and material sciences. In biomedicine, gold nanoparticles (AuNPs) are used in several purposes such as leukemia therapy, biomolecular immobilization, biosensor design and used as AuNPs as anti-angiogenesis, anti-malaria and anti-arthritic agents. Silver nanoparticles (AgNPs) are applied as selective coating agent for solar energy absorption, intercalation material for electric batteries, catalysts in chemical reactions and antimicrobial agents.

Physical methods

Preparation of nanometals using physical methods such as attrition and pyrolysis supply nanostructures with narrow and controlled size ranges, however, these methods require very expensive equipments and the final yield is low.

Biosynthesis

Microorganisms, both unicellular and multicellular, are known to produce inorganic materials often of nanoscale dimensions either intracellularly or extracellularly and the inherent uniformity of the biological structures can be combined with the functional properties of inorganic nanoparticles. For the biosynthesis of nanoparticles chloroauric acid (HAuCl4) and AgNO3 are used.

Crystallized and spherical-shaped Au and Au–Ag alloy nanoparticles have been synthesized and stabilized using a fungus, F. semitectum in an aqueous system. Aqueous solutions of chloroaurate ions for Au and chloroaurate and Ag+ ions (1 : 1 ratio) for Au–Ag alloy were treated with an extracellular filtrate of F. semitectum biomass.

Gold, silver and Au/Ag alloy nanoparticles can also be fabricated by dissolving pure enzyme in deionized water followed by adding aqueous concentration of HAuCl4, AgNO3 and Au/Ag.

Chemical reduction

AuNPs of various sizes and shapes can be synthesised by chemical reduction of gold salts such as hydrogen tetrachloroaurate (HAuCl4) using citrate as the reducing agent which produces monodisperse spherical AuNPs in the 10–20 nm diameter range. However, production of larger AuNPs (40–120 nm) by this method proceeds in low yields, often resulting in polydisperse particles. Monodisperse AuNPs can be synthesised by seeding approach to have diameters between 30 and 100 nm. This method uses the surface of AuNPs as a catalyst for the reduction of Au3+ by hydroxylamine.

Borohydride-reduced AuNPs seeds of 3 to 4 nm dia are mixed with gold salt growth solution, rod-shaped micellar template (cetyltrimethylammonium bromide; CTAB), reducing agent (ascorbic acid), and small amount of silver ions for shape induction to produce spheroid or rod-like gold nanoparticles.

Other methods

Other methods for the synthesis of AuNPs include physical reduction (hollow Au nanostructures in large-scale), photochemical reduction (cubic AuNPs), biological reduction (molecular hydrogels of peptide amphiphiles for producing various shapes of AuNPs), and solvent evaporation techniques (2D Au super lattices). A simple and potentially cost effective method is microwave irradiation approach for the synthesis of shape-controlled AuNPs by which irradiation of Au salt, reduced in CTAB micellar media, in the presence of alkaline 2,7-dihydroxy naphthalene (2,7-DHN), generate exclusively spherical, polygonal, rods, and triangular AuNPs within few seconds.

Bimetallic AuNPs

Bimetallic AuNPs, such as Au–Ag, have also attracted attention due to their interesting catalytic, structural and electronic properties, and the sensitivity of their surface plasmon resonance (SPR) properties. Accordingly, the development of simple and robust methods for the synthesis of bimetallic nanoparticles is currently of great interest.

Spherical Au/Ag alloy nanoparticles whose SPR band could easily be tuned by varying the molar fractions of gold could be obtained by reduction of Au and Ag salt with sodium citrate in refluxing aqueous solution. A seed-mediated approach to synthesize Au-Ag core-shell nanorods from silver ions, using gold nanorods as seeds, has also been reported. Other methods for the synthesis of bimetallic AuNPs include sputter deposition technique in ionic liquids, photochemical synthesis, deposition of Au/Ag on silica and reverse microemulsion method to prepare silica-coated Au–Ag nanoparticles.

The AuNPs have unique chemical and optical properties, easy to fabricate and used in various molecular imaging and delivery applications. The unique biodistribution of AuNPs within tumors have led to the discovery of gold-based nanosystems as delivery vehicles for chemotherapeutic agents.

For bio imaging

Researchers have used various exogeneous agents to visualize key subcellular compartments. Cell imaging is achieved through the generation of colorimetric contrast between different cells/subcellular organelles by these imaging agents. Conventional exogeneous imaging agents such as lanthanide chelates and organic fluorophores are prone to photobleaching, low quantum yields, and broad emission window.

The shortcomings of the conventional imaging agents have limited their applications as biomedical diagnostic tools and have stimulated interest in typical nanomaterials, such as magnetic nanoparticles, Q-dots and AuNPs since they eliminate most of the vulnerabilities of the conventional imaging agents. But AuNPs are unique exceptions because they are more tolerable and compatible with cellular environment and more useful in many in vitro and in vivo application. In addition, the colorimetric contrast observed within the AuNPs treated cells could be controlled by size, shape or even surface modification of the AuNPs due to a phenomenon called surface plasmon resonance (SPR).

When excited, the SPR of AuNPs could scatter and/or absorb light in the visible or the near-infrared (NIR) spectrum by which in vivo optical imaging such as photoacoustic and two-photon luminescence imaging can be done as it generates cellular contrast by tuning the SPR of the AuNPs to the NIR spectrum. Other noninvasive diagnostic tools such as MRI and X-ray computed tomography (X-ray CT) have utilized AuNPs as contrasting agent due to the ease of surface modifi cation and higher X-ray absorption coefficient, respectively.

Graphene amplifier

2012-01-01T10:00:00.000-08:00

Voltage amplifier
A voltage amplifier device capable of amplifying small alternating voltage signals. The voltage amplifier is the main building block in analogue electronics. Amplification or voltage gain must be larger than 1 if the device is to be called an amplifier.
Graphene
Graphene is an allotrope of carbon, whose structure is one-atom-thick planar sheets and is most easily visualized as an atomic-scale chicken wire made of carbon atoms and their bonds. The crystalline or "flake" form of graphite consists of many graphene sheets stacked together. Graphene differs from most conventional three-dimensional materials. Intrinsic graphene is a semi-metal or zero-gap semiconductor and has remarkably high electron mobility at room temperature.
Graphene exhibits a minimum conductivity which is still unclear. However, rippling of the graphene sheet or ionized impurities in the SiO2 substrate may lead to local puddles of carriers that allow conduction. Graphene has the ideal properties to be an excellent component of integrated circuits. Graphene has a high carrier mobility, as well as low noise, allowing it to be used as the channel in a FET. The issue is that single sheets of graphene are hard to produce, and even harder to make on top of an appropriate substrate. But many scientists believe that it cannot compete with silicon in applications requiring voltage amplification, like analogue amplifiers and digital logic gates.
Graphene amplifier
A triple-mode single-transistor graphene amplifier was made by researchers of University of California, Riverside and Rice University capable of amplification of 0.02 which was only an attenuator and not an amplifier.
There was only one previous report of voltage amplification in a graphene device, which itself proved difficult to fabricate. The device was not integrated either and so required external metal inductors and capacitors to operate. Moreover, the voltage gain achieved was not large enough for general use. Also it is no easy task to obtain signal amplification in graphene devices.
Without voltage amplification though, graphene electronic devices will be mostly limited to high-frequency (more than 100 GHz) analogue mixers. As analogue electronics cannot exist without voltage amplifiers, graphene devices would need to be integrated with silicon transistors for this most important task of signal amplification
The first graphene device capable of significant voltage amplification (more than 10 dB) which could compete head-on with silicon as the material of choice in electronics has been fabricated by researchers in Italy.
According to researchers, even though it is their first graphene amplifier, it already shows a remarkable performance with a flat frequency response well exceeding the audio range (more than 20 kHz) and a very low total harmonic distortion (less than 1%).
Researchers believe that graphene should not just be confined to specialist, low-voltage gain, and high-frequency applications but can challenge silicon head-on in voltage amplification. They also feel that amplification of audio signals in audio voltage amplifiers which are the main components of home-theatres and iPods, for example, could now be possible using graphene.

NEW YEAR GREETINGS

2011-12-31T07:44:00.000-08:00

Nanoall - Nanotechnology Blog
wishes all readers
Happy and Prosperous New Year 2012

Nanowire endoscope for cell

2011-12-31T07:40:00.000-08:00

Nanowire
A nanowire is a nanostructure that has a thickness or diameter constrained to tens of nanometers or less and an unconstrained length in which quantum mechanical effects are important. Many different types of nanowires exist, including metallic (e.g., Ni, Pt, Au), semi conducting (e.g., Si, InP, GaN, etc.), and insulating (e.g., SiO2, TiO2). Molecular nanowires are composed of repeating molecular units either organic (e.g. DNA) or inorganic (e.g. Mo6S9-xIx). The nanowires could be used to link tiny components into extremely small circuits created out of chemical compounds.
Nanowires probe
Researchers at the Lawrence Berkeley National Lab in the US have made their device by attaching a tin oxide nanowire waveguide to the tapered end of an optical fibre. Light traveling along the fibre can be effectively coupled into the nanowire. This robust nanowire probe can be used as a non-invasive endoscope to image the inside of living cells. It can also be used to transport tiny "cargo", in medical applications to deliver genes, proteins and therapeutic drugs into biological cells.
Principle
According to the researchers by combining the advantages of nanowire waveguides and fibre-optic fluorescence imaging, we can manipulate light at the nanoscale inside living cells for studying biological processes within single living cells with high spatial and temporal resolution. Advances in nanophotonics have made it possible to overcome the diffraction limitations of current techniques and the fluorescence sensing techniques use sub-micron tapered optical fibres which can image sub-cellular components only by rupturing cell membranes.
But the developed device can provide high-resolution optical images of the inside of a single living cell when the tip is inserted into the cell and light is passed. The nanowire can be re-used many times because it is flexible and can be repeatedly bent and buckled. The light emitted from the endoscope was closely confined to the nanowire tip and can provide highly directional and localized illumination.
The endoscope is also non-invasive because it can be safely inserted into a cell cytoplasm without causing any damage to the cell. The blue light emitted by the nanoprobe is not dangerous as the volume illuminated is very small in the order of picolitres.
Applications
Although single-cell delivery systems based on carbon and boron nitride nanotubes already exist, such devices have relatively long delivery times of up to 30 minutes. The new nanowire probes are much quicker and release quantum dot cargo into the target cells in just one minute.
This nanowire endoscope can be used to do point-delivery of genes, proteins, therapeutic drugs or other cargo with high spatial resolution and may also be used to electrically or optically stimulate a living cell with a simultaneous high-solution optical signal being output from the same nanowire probe.

For more about the research of Peidong Yang and his group, visit the Website at http://www.cchem.berkeley.edu/pdygrp/main.html

Nanobio materials in medical applications

2011-12-25T04:48:00.000-08:00

Nanotechnology plays an important role in biomedical and medical industry applications. Some of the applications are: tissue engineering, detection of protein, drug and gene delivery, probing of DNA structure, separation and purification of biological molecules and cells, etc.

Nano particles are compatible in size to the protein dimensions making it appropriate for bio tagging or labeling. In addition, the biological tags, where the interaction with biological target happens by biological coating or layer of biopolymers and antibodies attached to nanoparticles. Nanomaterial is able to fluoresce or change optical properties. These behaviors result in biocompatible property for nanomaterials.

Nano biomaterials are widely used in medicine and biological applications. Some recent developments for medicine applications are; tissue engineering, detection of protein and cancer therapy, medical imaging using quantum dots or chromophores synthesis for cancer diagnosis and drug delivery systems with benefit of targeting a specific cell for delivery with more therapy efficacy.

Tissue engineering and cancer therapy

Tissue engineering

In the tissue engineering, as the smooth surface of the artificial bone will be rejected by the body, it is coated with nanoparticles to overcome this problem, but suffers from the lack of bioactivity, like titanium. Therefore, the approaches were made to use apatite coating on titanium which resulted in thick non-uniform and poor adhesion surfaces. Hence making apatite from the simulated body fluid has an advantage of strong adherent and uniform layers.

Cancer therapy

prostate cancer

For treating cancers it is usually difficult to get the right amount of each drug to the tumor where combination drug therapy is more effective than single drugs. Researchers at MIT and Brigham and Women’s Hospital have developed a nanoparticle that can deliver precise doses of two or more drugs to prostate cancer cells. The researchers tailored their particles to deliver cisplatin and docetaxel, two drugs commonly used to treat many different types of cancer. Such particles could improve the effectiveness of chemotherapy while minimizing the side effects normally seen with these drugs, and could also be adapted to target cancers other than prostate cancer, or even to deliver drugs for other diseases that require combination therapy.

Once the drugs are loaded into the nanoparticle, the researchers add a tag that binds to a molecule called PSMA, which is located on the surfaces of most prostate tumor cells. This tag allows the nanoparticles to go directly to their target, bypassing healthy tissues and potentially reducing the side effects caused by most chemotherapy drugs.

Human PC-3 prostate cells and a non-malignant fibroblast cell line incubated with the carbon coated nanomagnets did not experience major cytotoxic (cell-destroying) effects. The cell cycle distribution and the apoptosis rate were not impaired by the presence of nanomagnets, reflecting the biocompatible character of these structures. This breakthrough provides an effective treatment option for many types of cancer, without the destruction of surrounding cells associated with chemotherapy or invasive surgery.

brain cancer

Recent studies show that titanium dioxide nanoparticles, a type of light-sensitive material widely used in sunscreens, cosmetics, and even wastewater treatment, can destroy some cancer cells when the chemical is exposed to ultraviolet light. But there was difficulty in getting nanoparticles to target and enter cancer cells while avoiding healthy cells.

Titanium dioxide nanoparticles chemically linked to an antibody can recognize and get attached to glioblastoma multiforme (GBM) cells. Scientists in Illinois have discovered that when they exposed cultured human GMB cells to these so-called "nanobio hybrids," the nanoparticles killed up to 80 percent of the brain cancer cells after 5 minutes of exposure to focused white light. The results suggest that these nanoparticles could become a promising part of brain cancer therapy, when used during surgery.

tumor

Researchers from the University of Hull have discovered a way to load up nanoparticles with large numbers of light-sensitive molecules to create a more effective form of photodynamic therapy (PDT) for treating cancer. The nanoparticles have also been designed to be the perfect size and shape to penetrate easily into the tumor. The nanoparticles are made from a material that limits the leaching of its contents while in the bloodstream, but when activated with light, at the tumor, the toxic reactive oxygen species can diffuse freely out of the particles; so that that damage is confined to the area of the cancer.

Nanowires

2011-12-23T10:50:00.000-08:00

Nanowires
A nanowire is a nanostructure and a solid, cylindrical wire with a diameter usually less than 100 nm or structures that have a thickness or diameter constrained to tens of nanometers or less and an unconstrained length where quantum mechanical effects are important.
Types
Many different types of nanowires exist, including metallic (e.g., Ni, Pt, Au), semi conducting (e.g., Si, InP, GaN, etc.), and insulating (e.g., SiO2, TiO2). Molecular nanowires are composed of repeating molecular units either organic (e.g. DNA) or inorganic (e.g. Mo6S9-xIx). The nanowires could be used to link tiny components into extremely small circuits.
Classification
Generally, nanowires are classified according to their structures: a) crystalline, those with structured alignments of polymer chains, b) polycrystalline, those with repeating chemical units for molecules, and c) nearly amorphous, those with random alignment of polymer chains. The varying shape is because the nanowire is only periodic along its axis. In all other dimensions, the nanowire will assume shapes are energetically favorable.
Fabrication
Nanowires are not naturally found but they can be fabricated from a wide variety of materials including germanium, metals, oxides, gallium nitrate, and silicon. There is no single standardized method for the fabrication of nanowires but can be done by nanolithography via an election beam and a relatively recent expensive method known as Molecular Beam Epitaxy (MBE) and by direct chemical synthesis by Vapor-Liquid-Solid (VLS) synthesis method.
High volume fabrication
Scientists at Harvard University in collaboration with researchers from the German universities of Jena, Gottingen, and Bremen, have developed a new technique for fabricating nanowire photonic and electronic integrated circuits that may one day be suitable for high-volume commercial production. By incorporating spin-on glass technology, used in Silicon integrated circuits manufacturing, and photolithography, transferring a circuit pattern onto a substrate with light, the team demonstrated a reproducible, high-volume, and low-cost fabrication method for integrating nanowire devices directly onto silicon. The structure of the team's nanowire devices is based on sandwich geometry: a nanowire is placed between the highly conductive substrate, which functions as a common bottom contact, and a top metallic contact, using spin-on glass as a spacer layer to prevent the metal contact from shorting to the substrate. As a result current can be uniformly injected along the length of the nanowires. These devices can then function as light-emitting diodes, with the color of light determined by the type of semiconductor nanowire used.
Semiconductor nanowires
Semiconductor nanowires are used in the development of cheaper and more efficient solar cells, as well as batteries with higher storage capacity and mainly in nanoelectronics. But, manufacturing semiconductor nanowires on an industrial scale is very expensive because of high temperatures at which they are produced using expensive catalysts, such as gold. But scientists at the Max Planck Institute have produced crystalline semiconductor nanowires at a much lower temperature using inexpensive catalysts, such as aluminium.
Nanowires for solar cell
University of California, San Diego electrical engineers have created experimental solar cells spiked with nanowires that could lead to highly efficient thin-film solar cells of the future. Indium phosphide (InP) nanowires can serve as electron superhighways that carry electrons kicked loose by photons of light directly to the device’s electron-attracting electrode and this scenario could boost thin-film solar cell efficiency.
Nanowire laser
Researchers have grown long, thin crystals of antimony-doped zinc oxide on a thin film of pure zinc oxide as nanowires. These nanowires have diameters of about 200 nm and are about 3 µm long and the ends of the nanowires were fused into a single crystal with the thin film underneath to work as an ultraviolet laser, producing light with a variety of wavelengths closely spaced around 385 nm.
Future developments
Already large-area lasing devices have been demonstrated, but the true potential of nanowires has now been realized. But the challenge is to fabricate single-nanowire laser diodes with ease. Researchers feel that the real significance of their research lies in developing single-nanowires lasers that could be used to study living cells so that they can insert this tiny laser into the cell or even smaller tissue inside the cell as it would be a powerful tool for doing basic biological and biomedical research into the single cell and perhaps even for killing viruses.

Measuring Nanoscale Temperature

2011-12-20T07:55:00.001-08:00

AFM tip
Atomic force microscope cantilever tips with integrated heaters are widely used to characterize polymer films in electronics and optical devices, pharmaceuticals, paints, and coatings. These heated tips are also used in research labs to explore new ideas in nanolithography and data storage, and to study fundamentals of nanometer-scale heat flow. Until now, however, no one has used a heated nano-tip for electronic measurements.
Nanoprobe
“We have developed a new kind of electro-thermal nanoprobe,” according to William King, a College of Engineering Bliss Professor in the Department of Mechanical Science and Engineering at Illinois. “Our electro-thermal nanoprobe can independently control voltage and temperature at a nanometer-scale point contact. It can also measure the temperature-dependent voltage at a nanometer-scale point contact.”
“Our goal is to perform electro-thermal measurements at the nanometer scale,” according to Patrick Fletcher, first author of the paper, “Thermoelectric voltage at a nanometer-scale heated tip point contact,” published in the journal Nanotechnology. “Our electro-thermal nanoprobe can be used to measure the nanometer-scale properties of materials such as semiconductors, thermoelectrics, and ferroelectrics.”
The electro-thermal probes are different than thermal nanoprobes typically used in King’s group and elsewhere. They have three electrical paths to the cantilever tip. Two of the paths carry heating current, while the third allows the nanometer-scale electrical measurement. The two electrical paths are separated by a diode junction fabricated into the tip. While the cantilever design is complex, the probes can be used in any atomic force microscope.

See for details: http://engineering.illinois.edu/news/2011/12/19/researchers-measure-nanometer-scale-temperature

Nanopore

2011-12-20T05:31:00.001-08:00

DNA
DNA is composed of four chemical bases: adenine, guanine, cytosine and thymine paired together in a complementary fashion and ordered in a species-specific sequence. The sequence represents a blueprint for the construction of the protein machinery to makes a cell work and store information. Sequencing of DNA involves cost and takes time because the procedure involves making multiple identical copies of the DNA and the chemistry involved.
Sequencing DNA with a nanopore is a revolutionary concept that may enable sequencing a single molecule of DNA, eliminating the need for amplification and for reducing the cost.
Nanopore
A nanopore is a hole made in a nanometre-thick thin membrane of materials such as silicon or silicon nitride. Nanopore is comparable in size to a DNA molecule.
Principle of DNA sequencing using nanopore
When the hole is immersed in electrolyte and a voltage applied across the membrane, a current flows through it. In addition to electrolytic ions, highly charged DNA molecules also try to electrophoretically migrate through the pore, but the hole is so small that only one molecule fits in the pore at a time.
By measuring either the voltage across the membrane or the current through the pore DNA is sequenced ,when each base pair as the DNA molecule translocates through the pore.
High-speed, high-fidelity sequencing can be done with low-noise electrical measurements at high frequency because the signal used to discriminate between bases is typically only at a microvolt or Pico amp level, and because the molecule translocates through the pore at a velocity of ~1 base pair per 10 ns.
Challenges
One of the main challenges is the signal-to-noise ratio required to discriminate between base pairs. The signal detection is limited by the bandwidth of the measurement and the corresponding electrical noise.
Researchers of University of Illinois, US, have reduced the high frequency noise in nanopores. With increased membrane thickness; miniaturized membrane area to reduce the parasitic capacitance; and by compensated membrane capacitance using an external electrical circuit the researchers have achieved this goal.
The reduction of the membrane capacitance is the key element to improving the overall electrical performance for sequencing DNA and the same has been proved by them by modeling the performance of its nanopore devices to show that further improvements in bandwidth and noise can be easily achieved by using thicker dielectric layers on top of the membrane.

Nanoblade for hydrogen storage

2011-12-18T06:00:00.001-08:00

Hydrides for storage
Hydrogen Storage is the bottleneck for on-board vehicle applications. Magnesium hydride is one of the most promising candidates for solid-state hydrogen storage due to its light weight, low cost and highly reversible hydrogen storage capacity of 7.6 mass% in MgH2. The high thermodynamic stability and sluggish reaction kinetics limit its practical applications. But making magnesium into nanostructures along with appropriate transition metal catalyst addition could solve the problems.
Nanoblade
Researchers at the University of Georgia, US, have designed and fabricated a vanadium-decorated magnesium nanoblade array structure by coating a thin layer of vanadium onto the two sides of individual magnesium nanoblades. The structures were made using a dynamic shadowing growth (DSG) technique, which is based on a physical vapor deposition method and combines oblique angle deposition (OAD) with substrate manipulation and source control.
Performance
The nanoblades are extremely thin magnesium-based structures, but their width gives them an incredible amount of surface area for their size. The role of vanadium coating as catalytic in the formation and decomposition of MgH2 and the unique nanoblade morphology with large surface area and small hydrogen diffusion length contribute to an overall improvement in hydrogen sorption performance. Specifically, the hydrogen sorption activation energy is reduced from 120–150 kJ/mol H2 for magnesium films or powders to ~35 kJ/mol H2, the hydrogen uptake and release temperatures are reduced even to room temperature, and the hydrogen loading and unloading times are reduced from 50 hours to several minutes.
Unlike three-dimensional springs and rods, nanoblades are extremely thin, with very large surface areas. They also are surprisingly spread out for a uniform nanomaterial, with one to two micron meters in between each blade. For hydrogen storage a large surface area is needed to provide room for the material to expand as more hydrogen atoms are stored. Arranging the nanoblades with microscopic spaces between one another allows them to expand and contract as they absorb hydrogen. The vast surface area of each nanoblade, coupled with the large spaces between each blade, could make them ideal for this application.
This finding could have applications for on-board vehicle applications and in energy storage and fuel cell technology. The nanoblades are also fully recyclable, an important criteria that was established by the Department of Energy for any hydrogen storing material.
Fabrication
To create the nanoblades, the researchers used oblique angle vapor deposition which is a widely used technique for building nanostructures by vaporizing a material, magnesium in this case and allowing the vaporized atoms to deposit on a surface at an angle. As the deposition angle changes, the structure of the material deposited on the surface also changes.
When deposited at zero degrees, the blades obtained are flat, flakey structures overlapping one another and when the deposition angle was increased the blade-like nature of these new nanomaterials becomes apparent. On further increase, the structures first tilted away from the magnesium vapor source instead of the expected inclination toward the source. The blades then quickly curved upward to form nearly vertical structures resembling nanoscale razorblades.

Golden nanocups for focusing light

2011-12-18T03:00:00.000-08:00

Scientists have used metallic nanoparticles to manipulate light in more effective ways than conventional optical materials to tap extra energy from the sunlight.
Metamaterials
Metamaterials have an edge over naturally occurring materials because they can cause dramatic physical effect with the interaction of light. These materials have very fine structures with features smaller than the wavelength of light which can pass on unique and fascinating optical behaviors.
Nanocups
The material having very tiny, cup-shaped particles called nanocups can collect light from any direction and emits it in a single direction.
Rice University researchers have used cup-shaped gold nanostructures which behave like three-dimensional nano-antennas to bend light in a more manipulative manner. The gold nanocups interrelate with light in two major ways: axially, the up-down direction, or transverse, the left-right track. The transverse mode is by far the more powerful of the two.
When the nanocups are illuminated, the transverse interaction exhibits a strong scattering resonance depending on the orientation of the cups, a property that has not been observed in studies of similar structures.
Production
Thin layers of gold are deposited from various angles onto polystyrene or latex nanoparticles. These are allocated haphazardly on a glass substrate. The cups that formed around the particles – and the dielectric particles themselves – are into an elastomer and lifted off of the substrate to produce transparent structures all oriented the same way.
This material derives its properties from its structure and not the composition but captures light from any direction and focuses it in a single direction. The material not only retransmits the color and brightness of what is behind, but also bends the light around, preserving the original phase information of the signal.
The scientists were able to lift the nanocups off of a structure and preserve their orientation.
Applications
Nanocup ensembles can focus light in a precise direction no matter where the incident light is coming. This factor can be used to its greatest advantage in thermal solar power. Capitalizing on this property, lots of money can be saved which is being spent on machinery. Because here a solar panel doesn’t have to track the sun yet focuses light into a beam that’s always on target. Utilizing nanocup metamaterial to pass on optical signals between computer chips has potential and enhanced spectroscopy and super lenses are also viable possibilities.

Frequency doubling with nanocups

2011-12-17T02:52:00.001-08:00

Researchers at Rice University in Houston, Texas have discovered a new type of material for converting red light into blue light.
Harmonic generation
Second harmonic generation (SHG) also called frequency doubling is a nonlinear optical process, in which photons interacting with a nonlinear material are effectively "combined" to form new photons with twice the energy, and therefore twice the frequency and half the wavelength of the initial photons.
The principle is that in quantum mechanics, the recolliding electron is represented as a de Broglie wave. This wave shifts over the molecular or atomic orbital, from which it was originally ionized. During this shifts, interferences occur, that modulate the amplitude and phase of the harmonic radiation.
Nanocups
Nanocups are three-dimensional artificially designed plasmonic nanostructures. Second harmonic generation is an important nonlinear optical process that has been used since the 1960s for making new light sources, optical crystals and the effect is widely used by the laser industry and in metrology applications in which two photons are converted into a single photon with twice the energy, and therefore twice the frequency or half the wavelength of the initial photons. The process was first demonstrated in 1961 when researchers focused a ruby laser with a wavelength of 694 nm into a quartz sample and observed that the light subsequently emitted had a wavelength of 347 nm.
Properties
Nanocup (or half-shell) consists of a dielectric nanoparticle upon which a semicircle layer of metal has been deposited. The device possesses "plasmonic resonances" – collective oscillations of the metal's conduction electrons – that can strongly interact with light at certain resonance frequencies. The resonances of this structure respond to both the electric and magnetic field components of light, and possess unique light-refractive properties.
Second harmonic UV light can be generated from individual nanocups by tuning the magnetic plasmon resonance to the incoming laser light beam with a wavelength of 800 nm. The intensity of the SHG can be increased by tilting the nanoparticle with respect to the incoming laser light and as the angle between the incident beam and the symmetry axis of the nanocup is increased.
Nanocup morphologies
The synthesis of carbon nanostructures, with interesting morphologies, has created a revolution in nanotechnology; carbon nanotube is a case in point, but other nanoscale morphologies of graphitic carbon could provide compelling uses. In particular short structures, including very short nanotubes, have proven impossible to be grown by existing techniques due to the difficulty in controlling and terminating growth during initial stages.
Architectures engineered from graphitic carbon, having up to 105 times smaller length/diameter (L/D) ratios compared to conventional nanotubes, reveal unique morphologies of nanocups, nanorings, and large area connected nanocup arrays. Such highly engineered hollow nanostructures can be fabricated using precisely controlled short nanopores inside anodic aluminum oxide templates.
The nanocups can be effectively used to hold and contain other nanomaterials, for example, metal nanoparticles, leading to the formation of multi component hybrid nanostructures with unusual morphologies. They can open up possibilities to integrate new morphologies of graphitic carbon in nanotechnology applications.
Applications
Nanocups have the ability to bend light in a specific direction. The nanocups could also be integrated into silicon photonics for on-chip optical sources or for measurements in future work. Nanocups could lead to the development of other, similar types of nonlinear optical materials that are designed to work at specific wavelengths of light, say, in the infrared or ultraviolet, or at wavelengths that are currently inaccessible to existing nonlinear optical materials.
According to the researchers, photonic devices, such as optical parametric oscillators or amplifiers and electro-optic or acousto-optic modulators could be made using these types of structures.

Making Plasmonics with Silver Polyhedral Nanocrystals

2011-12-15T22:42:00.000-08:00

Plasmonics
Nanoscale fabrication (such as focused ion beam lithography techniques) allow one to make new materials with increasing sophistication and freedom of design, but controlling light at the nanoscale remains a challenge. Traditionally light can only be controlled on length scales down to a little below the wavelength of light, a few hundred nanometers, hence the usual resolution limit of optical microscopes and telescopes.
Plasmonics is the phenomenon by which a beam of light is confined in ultra-cramped spaces allowing it to be manipulated as desired. Plamonics is thought to embody the strongest points of both optical and electronic data transfer, allowing the fast transmission of information over very small wires. Plasmonics, sometimes called "light on a wire," would allow the transmission of data at optical frequencies along the surface of a tiny metal wire, despite the fact that the data travels in the form of electron density distributions rather than photons.
Plasmonics will be useful in controlling the optical properties of molecules, and in using optics to monitor molecules. Understanding the new physics involved will enable progress in biology, chemistry and materials science, and will enable new devices and new materials to be made. Plasmonics holds great promise for super fast computers, microscopes that can see nanoscale objects with visible light, and even the creation of invisibility carpets.
A major challenge for developing plasmonic technology, however, is the difficulty of fabricating metamaterials with nano-sized interfaces between noble metals and dielectrics.
Researchers at U.S. Department of Energy Lawrence Berkeley Lab have developed a simple approach to fabricate plasmonic materials by inducing polyhedral-shaped silver nanocrystals to self-assemble into three-dimensional super crystals of the highest possible density.
Silver nanocrystals
Researchers made silver nanocrystals of a variety of polyhedral shapes self-assembled into millimeter-sized superstructures through a simple sedimentation technique based on gravity. Nanoscale silver polyhedral crystals can self-assemble into structures with densest packing of these shapes.
Polyol synthesis technique can be used to generate silver nanocrystals in various shapes, including cubes, truncated cubes, cuboctahedra, truncated octahedra and octahedra over a range of sizes from 100 to 300 nanometers. These uniform polyhedral nanocrystals when placed in solution get assembled themselves into dense super crystals through gravitational sedimentation.
Precise control of the super lattice dimensions can be obtained in bulk solution when the assembly takes place in the reservoirs of micro array channels.
Thus a dilute solution of nanoparticles is loaded into a reservoir and then tilted to make the particles to gradually sediment and assemble at the bottom of the reservoir and more concentrated solutions or higher angles of tilt causes the assemblies to form more quickly.
The assemblies generated by this sedimentation procedure exhibited both translational and rotational order over exceptional length scales. In the cases of cubes, truncated octahedra and octahedra, the structures of the dense super crystals corresponded precisely to their densest lattice packing. Although sedimentation-driven assembly is not new, for the first time the technique has been used to make large-scale assemblies of highly uniform polyhedral particles.
When compared with crystal structures of spherical particles, dense packing of polyhedra are characterized by higher packing fractions, larger interfaces between particles, and different geometries of voids and gaps, which will determine the electrical and optical properties of these materials.
The silver nanocrystals used by researchers are excellent plasmonic materials for surface-enhanced applications, such as sensing, nanophotonics and photo catalysis. Packing the nanocrystals into three-dimensional super crystals allows them to be used as metamaterials with the unique optical properties that make plasmonic technology so intriguing.

Nanoparticle Electrode for Storage Batteries

2011-12-15T18:54:00.000-08:00

For making wind and solar power usable on a grand scale there is a need for an efficient, durable, high-power, rechargeable battery to store large quantities of excess power generated. Conventionally lithium ion batteries are used in most applications.
Lithium ion batteries
The conventional lithium ion batteries have a high energy density so that they can hold a lot of charge for their size, making them great for portable electronics such as laptop computers. But energy density is not very important as for as storage on the power grid is concerned while cost is a greater concern. Some of the components in lithium ion batteries are so expensive that the batteries on a scale for use in the power grid will ever be economical. Also lithium ion battery can handle only about 400 charge/discharge cycles before it deteriorates too much to be of practical use.
Battery electrode
An electrode in an electrochemical cell is referred to as either an anode or a cathode (words that were by Faraday). The anode is the electrode at which electrons leave the cell and oxidation occurs, and the cathode is the electrode at which electrons enter the cell and reduction occurs. Each electrode may become either the anode or the cathode depending on the direction of current through the cell. When the battery is connected to an external load, or device to be powered, the negative electrode supplies a current of electrons that flow through the load and are accepted by the positive electrode. When the external load is removed the reaction ceases. Most batteries fail because of accumulated damage to an electrode's crystal structure.
New electrode
Stanford researchers have used nanoparticles of a copper compound to develop an efficient, durable, inexpensive and high-power battery electrode for making batteries big enough for economical large-scale energy storage on the electrical grid. The battery electrode is made of crystalline hexacyanoferrate nanoparticles of copper.
The batteries constructed using these electrodes could solve the problem of sharp drop-offs in the output of wind and solar systems due to minor changes in weather conditions. The electrode of the developed battery survived 40,000 cycles of charging and discharging, after which it could still be charged to more than 80 percent of its original charge capacity and it is predicted that this electrode may serve a life period of up to 30 years on the electrical grid.
The atomic structure of the crystalline copper of the new electrode has an open framework to allow ions which move en masse either to charge or discharge a battery without damaging the electrode. The right-sized ion turned out to be hydrated potassium is a much better fit compared with other hydrated ions such as sodium and lithium.
Because the ions can move so freely, the electrode's cycle of charging and discharging is extremely fast, which is important because the power output of a battery is proportional to how fast the electrodes are discharged.
The speed of the electrode is further enhanced due to a particles size of 100 atoms of electrode material which makes the ions travel very far into the electrode to react with active sites in a particle to charge the electrode to its maximum capacity, or to get back out during discharge.
The researchers chose to use a water-based electrolyte, which is claimed to be basically free compared to the cost of an organic electrolyte used in lithium ion batteries. They made the battery electric materials from readily available precursors such as iron, copper, carbon and nitrogen which is inexpensive compared with lithium.
Limitation
The limitation of the new electrode is that its chemical properties cause it to be usable only as a high voltage electrode. But the battery is made of two electrodes; a high voltage cathode and a low voltage anode in order to create the voltage difference to produces electricity. The researchers need to find another material to use for the anode before they can build an actual battery.

Potential Uses of Nanotechnology

2011-12-15T08:17:00.000-08:00

See the video on potential uses of nanotechnology

Nanotechnology for never weting fabrics - video

2011-12-15T08:12:00.000-08:00

See the super power of nanotechnology in this video.

superhydrophobic spray-on nanocoating

2011-12-15T08:08:00.000-08:00

See a video on NeverWet, a silicon-based spray-on coating that repels water and heavy oils.

Graphene absorbs infrared light

2011-12-15T06:58:00.001-08:00

Graphene can absorb more than 2% of incident visible light, but researchers at IBM have discovered that graphene can absorb up to 40% of light in the far infrared and microwave frequency ranges. The finding confirms that the material could be ideal for terahertz applications.
Graphene
Graphene is a 2D sheet of carbon just one atom thick with unique electronic and mechanical properties. Graphene has a number of technological applications and can even replace silicon in the electronic industry. This is because electrons travel through graphene at extremely high speeds with no rest mass.
It can also absorb light over a very wide range of wavelengths, ranging from the visible to the infrared. This is unlike III-V semiconductors that do not work over such a wide range.
Infrared light
The infrared part of the electromagnetic spectrum is important for optical telecommunications, for example, and the terahertz range in areas like biological imaging, materials analysis and security screening. Characterizing graphene at these wavelengths is thus crucial for developing graphene optoelectronic devices for such applications.
Infrared radiation absorption
The IBM researchers in New York had already analyzed the infrared radiation emitted from graphene, determined the temperature distribution, carrier (electron and hole) densities and the position of band structure where the valence and conduction bands touch. The Fermi level of undoped (or intrinsic) graphene coincides with the Dirac point, and the position of this point is crucial for defining graphene's properties.
The researchers have studied few-layer wafer-scale epitaxial and single-layer CVD graphene using infrared spectroscopy and were able to obtain information on the sheet resistance and the rate at which free carriers are scattered during transport.
According to the researchers the finding opens up avenues for applications in transparent terahertz optoelectronics, terahertz infrared metamaterials, cloaking, transformation optics and photonics applications.
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Nanocages to treat tumour

2011-12-12T08:08:00.000-08:00

Researchers at Washington University in St Louis have used photo acoustic tomography, a non-invasive imaging technique to understand the transport kinetics of gold nanocages in the lymphatic system. The technique could be used to design new tools for cancer therapy.
Gold nanocages
Gold nanocages were invented by Younan Xia and colleagues at Washington University. These nanostructures have hollow interiors having diameter typically between 30–100 nm and ultra thin porous walls. The structures can be designed to absorb strongly and scatter light in the near-infrared (IR) region of 700–900 nm in the electromagnetic spectrum.
Conventional methods
Tumors spread by invading adjacent issue and cancerous cells propagate throughout the lymphatic system and then into the blood stream. The closest lymph node that drains from a tumor is called the sentinel lymph node (SLN) and this is most likely the area from which metastasis starts. Conventional methods based on injecting organic dyes and hazardous radioactive colloids require surgery. Sentinel lymph node biopsy is an invasive procedure that is used routinely for which SLN mapping is the prerequisite for biopsy. Gold nanoparticles were also earlier used to treat the cancer. Combining the gold nanostructures with specific antibodies or peptides allows them to damage targeted cancerous tissue when illuminated with light at wavelengths around the absorption peak of the gold nanoparticles.
Present technique
The researchers found by injecting a solution of gold nanocages that it traveled through the lymphatic system and accumulated in the lymph nodes of the test animal using reflection-mode photo acoustic imaging technique. The technique relies on pulsing the area of interest with near-IR light from a laser and analyzing the photo acoustic signals generated subsequently by the nanocages therein. The present technique can pinpoint the location of the nanocages accumulated in an SLN at up to 70 nm deep in tissue. The present technique is a non-invasive photo acoustic SLN mapping based on gold nanocages which could be used to greatly aid minimally invasive methods such as fine-needle aspiration biopsy.

Nanoscale modeling

2011-12-12T03:09:00.000-08:00

MIT simulation tools
This set of simulation tools has been developed to provide students with the fundamentals of computational problem-solving techniques that are used to understand and predict properties of nanoscale systems. Emphasis is placed on how to use simulations effectively, intelligently, and cohesively to predict properties that occur at the nanoscale for real systems. The course is designed to present a broad overview of computational nanoscience and is therefore suitable for both experimental and theoretical researchers. These tools have been updated throughout spring term of 2011. The simulations are run by the tool are: Averages and Error Bars, Molecular Dynamics (Lennard-Jones), Molecular Dynamics (Carbon Nanostructures), Monte Carlo (Hard Sphere), Monte Carlo (Ising Model), Quantum Chemistry (GAMESS), Quantum Chemistry (Quantum Espresso), Density Functional Theory (Siesta), and Quantum Monte Carlo (QWalk).
Purdue University modeling kit for quantum dot devices
Quantum dots
A quantum dot is a portion of matter such as semiconductor whose excitons are confined in all three spatial dimensions having electronic properties intermediate between bulk semiconductors and discrete molecules. Quantum dots are a revolutionizing material where traditional semiconductors fall short. Quantum dots exhibit extraordinary electronic properties allow charge control down to atomic scales and are used in the world's smallest transistor – a quantum dot transistor built of seven atoms.
Quantum dot model
Simulating quantum and atomistic effects for realistic devices is computationally challenging, and thus is often narrowed to unrealistically small structures. Researchers at Modeling Group at Purdue University, US, have modeled real quantum dot devices atom-by-atom at very high precision with the help of supercomputer. With supercomputing and advanced simulation tools Purdue engineers try to model real world nanodevices.
The researchers have reconstructed the optical emission spectrum of an InGaAs quantum dot molecule using NEMO 3D – a semiconductor device simulation tool developed at NASA and Purdue. From the emission spectra and NEMO 3D results, important quantum dot geometry parameters have been identified. NEMO 3D nanoelectronic modeling tool can evaluate structures with more than 50 million atoms through parallelized computation.

Nanoparticle tattoo to monitor health

2011-12-12T02:34:00.000-08:00

Diabetes is a common disease with all age group, and despite decades of medical advancement, measuring accurately the glucose level in the human body is still a problem because it involves the daily task of pricking their fingers to check glucose levels.
Sensing system
MIT researchers have reported about a sensing system that consists of a “tattoo” of nanoparticles injected below the skin to detect glucose. The device can be worn over the tattoo to clearly display glucose level. The tattoo material consists of carbon nanotubes which are injected under the skin. Nanotubes are wrapped in glucose-responsive polymers and when the polymers encounter blood sugar, they cause the nanotubes to flash light. The sensor recognizes this flashed light with near-infrared detection. Nanotubes are unique resilient to light exposure and hence the device can provide constant information on blood glucose level without damaging the particles.
Nanoparticle solution
Adding functionality to body art, researchers at Northeastern University have developed a nanoparticle solution which, when injected into the skin and scanned by an iPhone, can reveal the inner workings of the body. Based on how the nanoparticles behave, an athlete can determine his sodium levels and the likelihood of dehydration mid-game. Within seconds, the blood-oxygen content of an anemic patient could be also be analyzed by a doctor.
Tattoo ink
Researchers at Charles Stark Draper Laboratories in Boston, USA have developed a unique tattoo ink for diabetics that changes color depending on glucose concentrations in the body and would allow continuous monitoring of blood sugar levels.
Originally conceived to monitor blood sodium levels for the treatment of heart problems and dehydration, the tattoo ink is made up of tiny porous nanoparticles, which are just 120 nanometres across. Each nanoparticle contains both molecules that detect glucose and a color-changing dye. The glucose-sensitive ink would need to be injected into surface layers of the skin, but the tattoo would only need to be a few millimeters in size. The ink can be reapplied regularly to avoid the problem like with regular tattoos.

Functionalized biocompatible CNTs

2011-12-10T09:32:00.000-08:00

Researchers at Stanford University have developed a technique to prepare conductive single-walled carbon nanotube films for biotechnology applications by depositing them on substrates coated with poly-L-lysine.
Poly-L-Lysine
Poly-L-Lysine is a synthetic amino acid chain that is positively charged and widely used as a coating to enhance cell attachment and adhesion to both plastic ware and glass surfaces. Poly-L-Lysine is normally used to cover tissue culture plates to help biological cells better stick to the plates. The molecular weight of Poly-L-Lysine can vary significantly with lower molecular weight (30,000 Da) being less viscous and higher molecular weight (>300,000 Da) having more binding sites per molecule.
Poly-L-Lysine is used to coat tissue culture plastic ware for enhanced cell attachment and adhesion. Coated surfaces will often improve cell attachment in reduced or serum-free conditions.
SWCNT
SWNTs on the market, regardless of which manufacturer produces them have 90% or 99% SWNTs content with Outer Diameter 1-2nm, inner Diameter 0.8-1.6nm and Length: 3-30um.
Single-walled carbon nanotubes have a wide range of unique electrical, mechanical and chemical properties and are thus promising for organic electronic applications, such as thin-film transistors, conducting electrodes and biosensors.
Nanostructures are used by researchers in biotechnology due to their exceptional electronic properties and ability to be functionalized.
SWCNTs have been used in bioelectronic devices, like drug delivery carriers and even scaffolds for tissue engineering. Researchers functionalize carbon nanotubes to make them more biocompatible, but the procedure is sometimes tedious and not always very efficient. But the present technique is simple and quick.
Functionalized surface
By soaking substrates, such as glass slides or silicon oxide wafers, in a solution of poly-L-lysine and depositing spin-coated carbon nanotubes onto the surface of the substrates hybrid material with a conducting surface can be created. The process can also be tuned to deposit specific amounts of SWCNTs on the slides and wafers.
As evident from scanning electron microscopy studies the SWCNT-PLL hybrid materials were found to be biocompatible by way of measuring cellular morphology in respect of metabolism and health.
Researchers found the SWCNTs to have little toxicity by monitoring mitochondrial activity in the cells and the cells had regular features or protrusions and retained a healthy and elongated shape.
Applications
Development of more biocompatible SWCNT surfaces will be useful in the field of bioelectronics and for developing conductive surfaces for biomedical applications.

Bangalore Nano Science Meet

2011-12-03T18:52:00.000-08:00

Banglore Nano Science Meet 2011 will start from 7 December 2011 in the IT city Banglore. The International conference will end on 9 December 2011. This is fourth edition of Bangalore Nano Science Meet. Prof. C.N.R. Rao, Chairman of Scientific Advisory Council to the Prime Minister of India, at the curtain raiser of the Bangalore Nano Science Meet on Friday said that at the age of 78, he works harder than techies in their 40s.
Prof. C.N.R Rao stated that the 4th Edition of Bangalore Nano Science Meet will have pre-conference turtorials for students and young researches on nano medicine and biotechnology, advance nano materials, nano in energy and environment, nano electronics and Microsystems.
Nano For Young is a programme put together by Prof. C.N.R. Rao and his team including Ajay K. Sood of Indian Institute of Science, Bangalore and Umesh Waghmare of Jawaharlal Nehtru Centre for Advanced Studies and Research where insightful discourses into nano research will be given by subject experts. 60 Scientists from countries such as USA, Netherlands, Australia apart from India will be speaking during the course of the international conference. There will be speakers from the reputed companies in the field.

Zeolite nanosheets

2011-11-29T10:29:00.000-08:00

Zeolites
Zeolites are materials that are traditionally used as absorbents, catalysts and as a filter for several decades. Zeolites are micro porous crystalline alumino silicates and widely used in petrochemistry and fine-chemical synthesis because strong acid sites within their uniform micro pores enable size- and shape-selective catalysis. In spite of this there have been substantial challenges in processing zeolitic materials into extended sheets that remain intact.
Zeolite nanosheets
Efforts to create zeolite nanosheets which are very small sieves to separate molecules from one another have proved rather fruitless as the processes used so far tend to result in the creation of holes in the sheet that are too large to capture the desire molecules. The result of blending the two layered zeolites silicate and its other component by melting them together is a nanocomposite that has two unique kinds of nanosheets. When making zeolites, the polystyrene in the mix is removed and this results in bent or curled sheets, which won’t work because it causes grouping or bunching which results in the development of holes that isn’t of the desired size. . Attempts to obtain a dispersed suspension of zeolite nanosheets via exfoliation of their lamellar precursors have been hampered because of their structure deterioration and morphological damage (fragmentation, curling, and aggregation).
Researchers at University of Minnesota have produced zeolites which results in deformed structures in the framework leading to holes in the material that are larger than the pores needed to capture whatever is being filtered.
The researchers used sound waves in the water soluble liquid toluene and a centrifuge and obtained flaky crystal type flat nanosheets having the right amount of thickness (2.6 and 3.4nm). The purity and morphological integrity of these nanosheets allow them to pack well on porous supports, facilitating the fabrication of molecular sieve membranes. The nanosheets were used to coat an anodised alumina membrane and a rough alpha-alumina support to produce zeolite membranes. Subsequent calcination gave smooth, well packed overlapping layers. The coated structures which were hydro thermally treated had reduced the space between the nanosheets and were highly effective at separating xylene isomers. Good performance was also observed for helium-hydrogen and helium-nitrogen mixtures.
Applications
The resultant product can be used to separate molecules as a sieve or as a membrane barrier in both research and industrial applications and the same process can be used to create other types of zeolites.
Thin zeolite films are attractive for a wide range of application. They can be used for making molecular sieve membranes, catalytic membrane reactors, permeation barriers, and low-dielectric-constant materials. Zeolites nanosheets could potentially be used for a wide range of applications such as sieves that can separate molecules based on their size and catalytic membranes. zeolite nanosheets that are only 2nm thick renders them highly active for the catalytic conversion of large organic molecules, and the reduced crystal thickness facilitates diffusion and thereby dramatically suppresses catalyst deactivation through coke deposition during methanol-to-gasoline conversion.

Nanotechnology helps devise Anti-Fog Glass

2011-11-23T02:14:00.000-08:00

Fog problems
There has never been a good solution for clearing fogged-up windshields of vehicles. Car windows, eyeglasses, camera lenses, a windscreen or a pair of glasses even bathroom mirrors keep fogging up. More than just a nuisance, fogging can pose a driving hazard. Glass fogs up when warm, moist air comes into contact with glass and cools so that thousands of tiny water droplets form on the glass. The droplets scatter light, making oncoming traffic hard to see. Most current solutions don't work: anti-fogging sprays are short-lived; and windshields coated with titanium dioxide require exposure at least every few hours to ultraviolet light to work.
Eliminating fog
The existing technologies for example put different types of materials onto that lens that promote this spreading of water using materials that really like water, in fact in some cases the very same materials that are used in diapers are used on the surfaces of lenses, for example, because they love to draw water and spread it out across the surface.
To address this problem researchers at MIT have come up with a coating that could prevent fog made of just tiny water droplets that scatter light from forming in the first place using a coating.
Coating composition
The superhydrophillic water loving coating is composed of nanoparticles made of silica, the same material that glass is made from, to create a coating with a rough surface, to keep moisture from blocking light although it looks smooth to the naked eye.
These very tiny particles of glass are assemble onto a surface using polymer chains. A polymer chain is a long chain-like molecule and in this case the developed the polymer chain has a positive charge, whereas the glass particles have a negative charge and positive to negative attractive force is used to build these layers up onto the surface. The net result is a very porous coating that has lots of holes in it.
The nanosilica particles form layers of tiny pores and the pores attract the tiny droplets of water that make up the foggy surface. Stacked ten to twenty layers thick, with air pockets in between, these pores create what's called a "wicking" effect, which forms the water droplets into a uniform sheet. When a droplet falls on that surface, the water is drawn into these pores instantaneously and wicked away into a uniform sheet. The net result is no water droplet is formed on the surface that can scatter light, but leaves a nice transparent lens in this case.
The researchers claim that this is a cheaply produced technology having added benefit of increasing the clarity of unfogged glass. It reduces the glare and allows more than 99 percent of light to pass through the glass, compared to untreated glass that scatters between four and eight percent of light. The coating also acts as an anti-reflection coating allowing more light to pass through.

Nanocoating to resists explosion and fire

2011-11-22T19:29:00.001-08:00

The US Navy wanted to find new ways to protect ships using coatings and polymers that could shield against explosions and fire. A research took off after the 9/11 attacks, with the new coating applied to rebuilt sections of the Pentagon. Office of Naval Research developed the coating with NanoSonic Inc., of Pembroke, VA. Harnessing nanotechnology and polymer science, the Navy has helped develop a spray-on protective coating that, depending on application thickness, makes surfaces blast-, ballistic- and fire-resistant.
Technology
NanoSonic makes the material using a patented, environmentally friendly, room-temperature nano-technology manufacturing process. The surface technology is called HybridSil Fire/Blast and acts like a force field that surrounds to protect any type of surface. Any existing material can be completely changed to make it more useful for the warfighter.
Properties
Few available materials provide explosions and fire resistant feature, but not both, since the properties are mutually exclusive with currently available material technologies. The material has fire-resistant properties. In Army and Air Force the coating can be used to protect buildings against vehicle-borne explosive devices.
The unique properties of these coatings are their ability to combine flame and blast protection. The material could be tailored for initial cure in 20 to 60 minutes at room temperature, followed by full cure within 24 hours in open-air environments.
Fire is one of the greatest threats on a ship or submarine. The coating can sprayed onto surfaces just like paint, with minimal surface preparation, applied in variable thicknesses; less for fireproofing and more for blast resistance.
Other coating technologies
Teslan Carbon Nanocoating, developed by Tesla NanoCoatings Ltd., of Massillon, OH, and the U.S. Army Corps of Engineers. Teslan is the first commercially available corrosion-resistant coating for steel made with fullerene carbon nanotubes (CNTs).
Nanostructured Antifogging Coatings, developed by Lawrence Berkeley National Laboratory. The durable, non-toxic antifogging and self-cleaning coating is intended for architectural glass, windshields, solar panels, and eyewear.
Electroplated Mn-Co Coating for Solid Oxide Fuel Cell Interconnects, developed by experts from the National Energy Technology Laboratory (Albany, OR), West Virginia University (Morgantown WV) and Faraday Technology Inc. (Clayton, OH).

Nanoplasmonic effect

2011-11-20T06:15:00.000-08:00

Nanoplasmonics
Nanoplasmonics is an upcoming field of research on tuned metallic nanostructures used to making tiny optoelectronics devices. Metallic nanoparticles interact strongly with light through localized surface plasmons and act as efficient optical nanoantennas. They can focus light to wavelengths dramatically below the diffraction limit. Nanoplasmonics research has revealed that diamagnetic particles can develop magneto-optical properties and a special type of magneto-optic Kerr effect can be noticed. Localized plasmonic modes have been seen in structures like gold/cobalt/gold nanosandwiches, gold-iron garnet perforated films and gold-coated maghaemite nanoparticles.
Researchers at Chalmers University in Sweden and nanoGUNE in Spain claim to have discovered a fundamentally new property in nanoscale metallic ferromagnets – the ability to control the sign of rotation of polarized scattered light. Researchers have found localized surface plasmons in purely ferromagnetic nanostructures. The researchers studied nickel nanodiscs grown on a glass substrate. Using a longitudinal magneto-optic Kerr effect setup (L-MOKE), the researchers showed "magnetoplasmonic" Kerr effect – whereby the polarization of light reflected by the disks depends on both magneto-optical coupling and simultaneous excitation of localized plasmons in the material.
Principle
When light with a certain polarization falls onto a nanosized magnetic ferromagnetic particle, the polarization will slightly rotate because magnetization changes the dielectric properties of the particle. This material is called magneto-optical as it changes the "non-diagonal" elements of a particle's polarizability tensor and such light also excites localized surfaces plasmons in the particle. Localized plasmons also change the particle's polarizability tensor but in its 'diagonal' elements.
Magneto-optics and nanoplasmonics work hand in hand, making the particle magnetoplasmonic. Without plasmons, the intrinsic magneto-optical effect rotates polarized light in one direction but when the particle is magnetoplasmonic this direction can be changed to the opposite one. This is what happens when Kerr rotation gets reversed. The researchers claim that they have discovered an extension of the "ordinary" magneto-optic Kerr effect, which describes how the polarization of light reflected by a ferromagnetic surface changes when an external magnetic field is applied.
Applications
This effect can be used to make biological and chemical sensors, because localized plasmons are very sensitive to their immediate dielectric environment. If the solution surrounding the plasmons is changed, the plasmon resonance in the material changes and this effect can be used in label-free sensing. Magnetoplasmonic nanostructures might also be employed as polarization-resolved light modulators in nanophotonics.

X-ray techniques for material analysis

2011-11-20T02:15:00.000-08:00

X-rays
X-rays were discovered in 1895 by German physicist Roentgen. X-rays are a form of electromagnetic radiation of very short wavelengths in the angstrom and nanometre region. To make images of the internal structure of bodies and objects X-rays are scattered by the internal lattices of solid objects and are used.
Crystal lattice
A crystal lattice of a material is a regular three-dimensional distribution (cubic, rhombic, etc.) of atoms in space arranged in such a way that they form a series of parallel planes separated from one another by a distance which varies according to the nature of the material. For any crystal, planes exist in a number of different orientations, each with its own specific spacing.
Constructive interference
When a monochromatic X-ray beam is projected onto a crystalline material at an angle, diffraction occurs only when the distance traveled by the rays reflected from successive planes differs by a complete number of wavelengths.
Bragg's Law
By varying the angle, the Bragg's Law conditions are satisfied by different spacing in polycrystalline materials. Plotting the angular positions and intensities of the resultant diffracted peaks of radiation produces a pattern, which is characteristic of the sample. Where a mixture of different phases is present, the resultant diffractogram is formed by addition of the individual patterns.
X-ray diffraction
X-ray diffraction is a tool for the investigation of the structure of matter and is a versatile, non-destructive technique that reveals detailed information about the chemical composition and crystallographic structure of natural and manufactured materials.
Using X-ray diffraction, a wealth of structural, physical and chemical information about a material investigated can be obtained. A host of application techniques for various material classes is available, each revealing its own specific details of the sample studied besides applying in chemical analysis, stress and strain measurement, the study of phase equilibrium, measurement of particle size, as well as crystal structure.
X-ray fluorescence (XRF)
The wavelength-dispersive x-ray fluorescence unit (XRF) is used chiefly for the determination of major element (Si, Al, Fe, Na, K, Mg, Ca, Mn, Ti, P) in rocks, minerals, ceramics, nanocompounds, cements, clays, alloys, etc. and major trace elements such as Rb, Sr, Y, Zr, Nb, Zn, Co, Cu, Ni, Ba, and Cr. Qualitative or semi-quantitative scans can be run on elements such as carbon through uranium.
Soft X-ray Appearance Potential Spectroscopy (SXAPS)
Soft X-ray Appearance Potential Spectroscopy SXAPS is a member of the Appearance Potential Spectroscopies. The experimental apparatus has a filament mounted near the sample which emits electrons which are accelerated towards the sample.
X-rays generated within the sample are detected via photoelectrons generated by the X-ray within the detector. SXAPS is not particularly surface sensitive, but as it is a threshold technique, the incident electrons will only travel a short distance before they are unable to excite the level of interest and suffers from poor signal.
Extended X-ray Absorption Fine Structure (EXAFS)
In EXAFS, operates with a monochromatic X-ray beam whose energy is gradually increased such that it traverses one of the absorption edges of the elements contained within the sample. Below the absorption edge, the photons cannot excite the electrons of the relevant atomic level and thus absorption is low.
The probability of X-ray absorption will depend on the photon energy (as the photoelectron energy will depend on the photon energy). The net result is a series of oscillations on the high photon energy side of the absorption edge. These oscillations can be used to determine the atomic number, distance and coordination number of the atoms surrounding the element whose absorption edge is being examined. The necessity to sweep the photon energy implies the use of synchrotron radiation in EXAFS experiments.
Extended X ray Absorption Fine Structure spectroscopy (REFLEXAFS)
By reflecting the X-rays from a surface at grazing incidence and detecting the resultant X-ray fluorescence with a Si(Li) detector, a more surface sensitive signal can be obtained. This technique is known as REFLEXAFS.
EDX - Energy Dispersive X-ray Analysis or EPMA - Electron Probe Micro Analysis
This technique is used in conjunction with SEM and is not a surface science technique. An electron beam strikes the surface of a conducting sample. This causes X-rays to be emitted from the point the material. The energy of the X-rays emitted depends on the material under examination. The X-rays are generated in a region about 2 microns in depth, and thus EDX is not a surface science technique. By moving the electron beam across the material an image of each element in the sample can be acquired in a manner similar to SAM. Due to the low X-ray intensity, images usually take a number of hours to acquire. Elements of low atomic number are difficult to detect by EDX.
NEXAFS - Near Edge X-ray Absorption Fine Structure and XANES - X-ray Absorption Near Edge Structure
If an X-ray has just sufficient energy to excite a core level, then the resultant photoelectron will leap into unoccupied states. This is the region that is explored by NEXAFS and XANES and is generally regarded as being the energy region between the absorption edge and where the EXAFS oscillations begin.
NEXAFS has particular application to chemisorbed molecules on surfaces. Information concerning the orientation of the molecule can be inferred from the polarization dependence. NEXAFS is sensitive to bond angles and frequently dominated by intra-molecular resonances of pi or sigma symmetry. The energy, intensity and polarization dependence of these resonances can be used to determine the orientation and intramolecular bond lengths of the molecule on the surface.
X-ray Absorption Near Edge Structure (XANES)
XANES can provide information about vacant orbitals, electronic configuration and site symmetry of the absorbing atom. The absolute position of the edge contains information about the oxidation state of the absorbing atom. In the near edge region, multiple scattering events dominate. Theoretical multiple scattering calculations are compared with experimental XANES spectra in order to determine the geometrical arrangement of the atoms surrounding the absorbing atom. Hence the technique provides complementary information to EXAFS.
Angle-resolved X-ray Photoelectron Spectroscopy
The effective sampling depth in XPS can be varied (for flat samples) by changing the angle of the sample with respect to the detector. The actual depth sampled, d, is given by the equation: d = 3λ sin θ, where λ is the inelastic mean free path of the photoelectron and θ is the angle between the sample surface and the analyzer acceptance plane.
By comparing the relative intensities of peaks at the same kinetic energy over a number of different takeoff angles it is possible to calculate layer thickness. Alternately, comparing relative intensities at low and high take off angles indicates whether a species is enriched or depleted in the surface region. This is useful for the analysis of thin films on surfaces where it is possible to determine the molecular orientation to the surface.
Angle Resolved X-Ray Photoelectron Spectroscopy (AR-XPS)
It is a non-destructive depth profile analysis of surfaces by measuring XPS data at surfaces of solid materials when changing the angle between analyzer acceptance axis and sample surface. Angle resolved XPS is an important tool for non-destructive near surface and ultra thin film analysis. The Ultra HSA provides the highest energy resolution at all take off angles as well as detecting very low concentrations of near surface species. Automated eucentric positioning of the sample ensures that the analysis position remains constant as the sample is tilted. Automatic charge neutralization allows all types of sample to be analysed by ARXPS automatically.

Gold nanoparticle helps detecting lung cancer

2011-11-20T00:20:00.000-08:00

Worldwide, lung cancer is the most common cause of cancer-related death people with the most common symptoms of shortness of breath, coughing and weight loss. It is a disease characterized by uncontrolled cell growth in tissues of the lung and if left untreated, this growth can spread beyond the lung.
Detection methods
A chest x-ray is usually the first test performed to evaluate lung cancer, sometimes if the chest x-ray is normal, and further tests are needed look for a suspected lung cancer. A CT scan is frequently the second step either to follow up on an abnormal chest x-ray, MRI is used to evaluate the possibility of lung cancer, a PET scan with radioactive material can be used to create colorful 3-dimensional image, Sputum cytology, bronchoscopy, fine needle aspiration, thoracentesis and a lot of other methods singly or in combination are used to detect lung cancer. Now a simple method has been developed using gold nanoparticles.
Gold nanoparticles for easy detection
Researchers at the University Of Colorado School Of Medicine have used gold nanoparticles in the development of a device for the non-traumatic, easy, cheap approach to early detection and differentiation of lung cancer. The metabolism of lung cancer patients differs from the metabolism of healthy people due to the difference in the molecules that make up cancer patients' exhaled breath. By comparing these molecular signatures to control groups, the device can detect not only if a lung is cancerous, but if the cancer is small-cell or non-small-cell, and adenocarcinoma or squamous cell carcinoma. The device was pioneered by the University of Colorado Cancer Center and Nobel-Prize-winning Technion University in Haifa, Israel.
Principle
The device distinguishes between the volatile organic compounds in cancer patients' exhaled breath compared to the breath of a control group. Subjects simply exhale into a bag, which separates superficial exhaled breath from breath that originated deeper in the lungs. And then this deep breath is analyzed by an array of gold nanoparticle sensors which immediately identify very small molecules to detect if the breath came from a cancerous lung.
It can measure the levels of volatile organic compounds against population scores to diagnose cancer and types of cancer, or can measure the change in patients' levels of VOCs across time. A breath now and a breath after treatment could define whether a patient should stay with a drug regimen or explores other options.
Applications
The device's potential uses go beyond diagnosis. This device could eventually help doctors quickly, simply, and inexpensively can distinguish between different types of lung cancer cells, define patients' lung cancer subtypes, specify correct therapies with subtypes early in the treatment process and more precisely target the disease. The device may also help doctors smooth the wrinkles in existing methods of cancer screening and measure to distinguish what are a benign nodule and a malignant nodule.

Graphene Growth

2011-11-17T11:46:00.001-08:00

Graphene has become a major research topic in physical sciences in recent years and has many potential applications. Graphene, carbon sheets are one atom thick and their properties have caused researchers and companies to consider using this material in several fields. One of the methodologies used to prepare graphene sheets is the chemical exfoliation of graphite in aqueous medium, which produces oxygen functionalized graphene sheets and the other method is to grow using copper. The quality of graphene depends on the crystal structure of the copper substrate it grows on. Graphene is a very important material and the future of electronics may depend on it but the quality of its production is one of the key unsolved problems.
Production
A very cost-effective, straightforward way to make graphene on a large scale is to grow on copper substrate. To produce large sheets of graphene, methane gas is piped into a furnace containing a sheet of copper foil. When the methane strikes the copper, the carbon-hydrogen bonds crack. Hydrogen escapes as gas, while the carbon sticks to the copper surface. The carbon atoms move around until they find each other and bond to make graphene. Copper is an appealing substrate because it is relatively cheap and promotes single-layer graphene growth, which is important for electronics applications.
While graphene grown on copper tends to be better than graphene grown on other substrates, it remains riddled with defects and multi-layer sections, precluding high-performance applications. Graphene grows in a single layer on the (111) copper surface and in islands and multilayer elsewhere. But researchers have speculated that the roughness of the copper surface may affect graphene growth.
Copper crystal structures
In fact copper foils are a patchwork of different crystal structures. As the methane falls onto the foil surface, the shapes of the copper crystals it encounters affect how well the carbon atoms form graphene. For making high-quality, high-performance electronics the copper's crystal structure is more important.
Different crystal shapes are assigned index numbers. Using several advanced imaging techniques, the researchers found that patches of copper with higher index numbers tend to have lower-quality graphene growth. Researchers also found that two common crystal structures, numbered (100) and (111), have the worst and the best growth, respectively. The (100) crystals have a cubic shape, with wide gaps between atoms. Meanwhile, (111) has a densely packed hexagonal structure.
In the (100) configuration the carbon atoms are more likely to stick in the holes in the copper on the atomic level, and then they stack vertically rather than diffusing out and growing laterally. The (111) surface is hexagonal, and graphene is also hexagonal. It is not a perfect match, but that there is a preferred match between the surfaces.
Cost
Researchers now are faced with balancing the cost of all (111) copper against the value of high-quality, defect-free graphene. It is possible to produce single-crystal copper, but it is difficult and prohibitively expensive. It may be possible to improve copper foil manufacturing so that it has a higher percentage of (111) crystals. Graphene grown on such foil would not be ideal, but may be good enough for most applications.
Future research
Researchers hope to use their methodology to study the growth of other two-dimensional materials, including insulators to improve graphene device performance. They also plan to follow up on their observations by growing graphene on single-crystal copper. The fact that there is a clear observational difference between these different growth indices helps steer the research and will probably lead to more quantitative experiments as well as better modeling.

Quantum membranes

2011-11-15T05:26:00.001-08:00

Quantum confinement effect
Due to quantum confinement the electronic and optical properties of a material changes as its size goes to around 10nm or less and using this property two dimensional semiconductors which are confined to operating in a two dimensional space can be created. Because of their unique properties, they can be put to use in highly specialized quantum optical and electrical applications. So far research on these semiconductors has been done using materials like graphene.
Quantum membranes
Nanoscale size effects drastically alter the fundamental properties of semiconductors. A team of researchers at the University of California, Berkeley, has developed a two-dimensional semiconductor called quantum membranes (QM) using indium arsenide having a band structure and can be turned from a bulk material to a two-dimensional one by reducing its size. The unique feature of QMs is that they can be used as a free standing material and thus can be used with a variety of substrates, unlike other such structures which are based on just a single one.
Quantum membrane fabrication
To make the QMs, indium arsenide is grown in a GaSb and AlGaSb substrate. Then the top layer is made into the required shape and the bottom layer is etched away. The remaining indium arsenide layer is then moved to whichever substrate is desired to make the final product.
Properties
In addition to adding a new material to the bank available to researchers in using semiconductor materials, the results of this work also provide insight into how structurally confined materials work which could lead to more materials with truly unique properties. The electrical properties of the material indicate that electron mobility does not depend on the field that was applied, except in the case of very high fields, which is quite different from conventional semiconductors.
Investigations have been carried out on the dominant role of quantum confinement in the field-effect device properties of free-standing InAs nano membranes with thicknesses varying from 5–50 nm.
Optical absorption studies were also performed by transferring InAs “quantum membranes” (QMs) onto transparent substrates, from which the quantized sub-bands are directly visualized.
It was observed by the researchers that these sub-bands determine the contact resistance of the system with the experimental values consistent with the expected number of quantum transport modes available for a given thickness. Also, the effective electron mobility of InAs QMs is shown to exhibit anomalous field and thickness dependences that are in distinct contrast to the conventional MOSFET models, arising from the strong quantum confinement of carriers. The researchers claim that results provide an important advance toward establishing the fundamental device physics of two-dimensional semiconductors.

Nanocapsules

2011-11-13T03:18:00.000-08:00

Nanocapsules
Nanocapsules have recently generated lot of interest in the area of controlled release with availability of biocompatible and biodegradable polymers. Nanocapsules are a specific class of nanoparticles composed of one or more active materials (core) and a protective matrix (shell). Nanocapsules are submicroscopic colloidal drug carrier systems composed of an oily or an aqueous core surrounded by a thin polymer membrane. The interfacial polymerization of a monomer or the interfacial nano deposition of a preformed polymer is the two technologies used to obtain such nanocapsules.
Preparation of nanocapsules
Nano precipitation method is used to prepare nanocapsules. The organic phase containing solvent, polymer, oil, and drug is pressed through the pores of an ultra filtration membrane via the filtrate side. The aqueous phase containing water and surfactant is made to circulate inside the membrane module, and sweep away the nanocaspules forming at the pore outlets.
Encapsulation technique
Encapsulation technology can be used to prepare micro/nanocapsules with specific application properties in several areas including food, biology and medicine. Nanocapsules can be synthesized via mini emulsion and interfacial polymerization techniques. Most reviewed nanocapsule technologies used in drug carrier systems employ encapsulation techniques using isocyanates in either solvent or bulk to form shell (or matrix) materials for encapsulating functional materials, releasable fill materials, or making pressure sensitive copying paper. The inherent reactivity of isocyanates with water makes it difficult to encapsulate them in aqueous media.
The nanocapsules can be characterized via Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM).
Two steps technique
The nanocapsules can be through two steps of pre-emulsification (to form a pre-emulsion) and emulsion polymerization. This gives a new method for synthesizing nanocapsules containing either blocked or free isocyanates in aqueous media. The thermally dissociated isocyanate can be utilized as an active functional group in coatings and adhesive applications. Nanocapsules containing blocked isocyanates are of interest in self-healing systems where the isocyanate can be liberated by thermal treatment or extracted via solvent or reactive agents such as amines. Nanocapsule shells functionalized with amines and hydroxyls provide a ready moiety for the isocyanate to react once it is liberated from the protective shell of the nanocapsule.
Nanocapsules of diltiazem
Diltiazem drug is widely used in the treatment of chronic conditions such as hypertension and angina which require prolonged therapy. Nanocapsules can be prepared by the interfacial deposition technique by taking different concentrations of polymers and phospholipid mixture. Nanocapsules of diltiazem can be prepared for achieving controlled release of the drug in order to reduce the frequency of administration of drug, to obtain more uniform plasma concentration, and to improve patient compliance.
The morphology of nanocapsules can be assessed by scanning electron microscope.
These nanocapsules are found to be smooth, spherical having distribution with particle size in the range of 20 to 380 nm, stable at 4°C but unstable at 25°C, and require storage in refrigeration. Thus nanocapsules are a useful technology for controlled release of diltiazem.

Nanobiomaterial applications

2011-11-10T10:54:00.000-08:00

Nanobiomaterials

Nanobiomaterials exhibit distinctive characteristics, including mechanical, electrical, and optical properties, which make them suitable for a variety of biological applications. Because of their versatility, they are poised to play a central role in nanobiotechnology and make significant contributions to biomedical research and healthcare.

Structure
Nanobiomaterial is made of nanoparticles, compounds of polymeric material and is used as surface for molecular assembly with membrane or nan-vesicle enclosed configuration. The size distribution is the major factor and controls material properties when using quantum-sized effects. The size control also leads to emit the lights through the wavelength to create biomarkers with recognized colors.
In nanobiomaterial, the core particle is covered usually by monolayers of inert material, like silica or organic material that are already absorbed on the surface. In many cases the layer of linker molecules is a compound of reactive groups at two ends, where one of the ends works as the connection to attach the linker to nanoparticle surface and other ends is used to attach moieties, such as antibodies.
Printing patterns
Printing of biomaterials at sub-cellular scales holds immense promise for studies in life sciences. The ability to create nanoscale patterns of DNA, proteins, lipids, biocompatible polymers and other biomaterials has the potential to revolutionize many areas of biological research and discovery, but until now the technology available to create these patterns has been overly complex, unacceptably slow, and unreliable.
Direct deposition
Recent advances in Dip Pen Nanolithography technology make possible the direct deposition of biologically relevant molecules onto a variety of surfaces. (Example: M/s NanoInk's Nano Fabrication Systems).
A new generation of Dip Pen Nanolithography instrument systems is available for biomaterials and cell biology applications. These systems can reliably print features ranging in size from tens of nanometers to ten microns with nanoscale registry, all under ambient conditions making it an indispensable tool for biomaterials research in the life sciences area.
Health care applications
Biomaterials are used to develop advanced medical devices to improve the course of human life. Nanobiomaterials can be used for human implant, orthopedics, drug delivery, gene therapy, antimicrobial treatments, array technologies, and diagnostics. Nanobiomaterials help with targeting, measuring, sensing, and imaging. They can also help enhance efficiency, safety, quality, and durability.
Biomedical applications
The field of medical diagnosis and treatment has recently seen significant improvements with the advent of many novel nanobiomaterials. Specific functionalization of the nanomaterials is imperative to improve stability, increase efficiency and reduce toxicity.
In biomedical fields, various materials are used for different purposes such as therapy, diagnostics, drug targeting, regenerative medicine and drugs. Some of them come into direct contact with blood and tissues in the human body, while many others are used in advanced medical equipment.
Recent developments in nanoscience and nanotechnology have provided new strategies for material design that are based on the structural control of atoms and molecules. These strategies have revolutionized the field of advanced functional materials. Their combination with the enormous amount of knowledge in molecular and cellular biology accumulated over the last few decades has lead to the conception of new medical technologies.
Cancer cure
Thousands of people die from malignant brain tumors every year, and the tumors are resistant to conventional therapies. This nanobiotechnology provides an alternative form of therapy that targets only cancer cells and does not affect normal living tissue. Scientists from the U.S. Department of Energy's (DOE) Argonne National Laboratory and the University of Chicago's Brain Tumor Center have developed a way to target brain cancer cells using inorganic titanium dioxide nanoparticles bonded to soft biological material.
Tissue engineering applications
Tissue engineering applications have an unquestionable potential to regenerate damaged tissues and organs. Artificial bladder, corneal epithelium, engineered skin are some of the tissue-engineered solutions, but most of the pathologies of interest are still to be solved. The stem cells technology has opened the door to large-scale production of “raw living matter” for cell replacement and boosted the overall sector in the last decade. Still reliable synthetic scaffolds fairly resembling the nanostructure of extra cellular matrices, showing mechanical properties comparable to those of the tissues to be regenerated and capable of being modularly functionalized with biological active motifs, became feasible only in the last years thanks to newly introduced nanotechnology techniques of material design, synthesis, and characterization. Nanostructured synthetic matrices look to be the next generation scaffolds, opening new powerful pathways for tissue regeneration and introducing new challenges at the same time. We here present a detailed overview of the advantages, applications, and limitations of nanostructured matrices with a focus on both electro spun and self-assembling scaffolds.
Anti-bacterial property
The researchers at University of Hong Kong have provided insights into the anti-bacterial and wound healing properties of silver nanoparticles, and demonstrated their promising anti-viral effects against HIV, Hepatitis B and H5N1 (bird flu). They also recently developed methods using nanomaterials to fix the brain and stop bleeding, and have a strong track record in nanomechanical research focusing on the degeneration of human intervertebral discs and medical implants.
Self-cleaning property
Researchers at Rensselaer Polytechnic Institute in Troy, NY used nanotechnology to design a self-cleaning plastic in which the enzyme molecules are an integral part of the material. When the plastic comes into contact with bacteria or other pathogens, the enzymes attack the microbes and destroy their ability to bind to its surface. Researchers attached enzymes to the surface of large carbon nanotubes which stabilize the enzymes, are then incorporated into a polymer. The technique could work for any number of enzymes including materials that kill specific microbes or even degrade oil sludge on contact. Coatings of the enzyme-polymer material could protect implantable medical devices from scar tissue formation. The unique properties of nanobiomaterials provide advantageous interactions with the proteins that control cellular function. Nanobiomaterials have an increased number of atoms and crystal grains at their surfaces and possess a higher surface area to volume ratio than conventional micro scale biomaterials. These differences in surface topography alter the corresponding surface energy for protein adsorption.
Biosensors application
Nanobiomaterial research has emerged as a new exciting field, recognized as a new interdisciplinary frontier in the field of life science and material science. Great advances in nanobiochip materials, nanoscale biomimetic materials, nanomotors, nanocomposite materials, interface biomaterials, nanobiosensors, and nano-drug-delivery systems have the enormous prospect in industrial, defense, and clinical medicine applications. Biomolecules assume the very important role in nanoscience and nanotechnology, for example, peptide nucleic acids (PNAs) replace DNA, act as a biomolecular tool/probe in the molecular genetics, diagnostics, cytogenetics, and have enormous potentials in pharmaceutics for the development of biosensors.
Catalyst application
Biological macromolecules such as proteins and DNA are versatile supports for organizing nanostructures and catalysts. Catalysts, including biocatalysts, capable of carrying out the multi-electron chemistry needed to produce solar fuels require multiple chemically distinct catalytic centers. These catalytic centers often involve metal ions in paramagnetic states to maximize reactivity and product distribution.
The application of nanotechnology to biomaterial science has a great potential, however it requires safe fabrication, commercial scale processing and the risk to human health and environment must not be overlooked.

Green Medicine by nano technology

2011-11-08T05:24:00.000-08:00

Green Medicine
Green or sustainable medicine is one that recognizes the link between the environment, medicine and human health and seeks to provide better health care while protecting the limited environmental and medical resources.
Researchers at the Nano-Science Center and the Department of Neuroscience and Pharmacology at the University of Copenhagen have characterized and tested how molecules react, combine together and form larger molecules, which can be used in the development of new medicine. The researchers claim that they are able to work with reactions that take place in very small volumes, namely 10-19 liters which is a billion times smaller than anyone has managed to work with before. Even more intriguing is the ability to do so in parallel for millions of samples on a single chip. This method will be of interest to industry because it makes it possible to investigate drugs faster, cheaper and greener.
Green production
Self-assembly is a fundamental principle in nature and occurs at all the different size scales, ranging from the formation of solar systems to the folding of DNA.Self-assembling systems, such as molecules, are biological systems that organize themselves without outside control. This occurs because some molecules fit with certain other molecules so well that they assemble together into a common structure.
By using nanotechnology observations can be made as to how specific self-assembling systems, such as biomolecules, react to different substances. The self-assembling systems consist entirely of biological materials such as fat and as a result do not impact the environment, in contrast to the materials commonly used in industry today (e.g. plastics, silicon and metals). This and the dramatic reduction in the amount of used materials makes the technique more environment friendly, 'greener'," according to the researchers.

Nano Spray Dryer

2011-11-08T05:16:00.000-08:00

The latest generation of instruments called the Nano Spray Dryer can generate particle sizes in the nano range. It can yield high quantities of material.
Spray drying is a gentle, continuous and scalable drying process to convert liquids to dry powders. The new Nano Spray Dryer is particularly suited to the needs of the pharmaceutical, biotech, material and nanotech markets, effective formulation of complex and valuable drugs and highly active pharmaceutical ingredients and nanoparticulates.
BUCHI Labortechnik AG in Flawil, Switzerland has developed an innovative piezoelectric atomizing technology for fine particles in the submicron range with narrow particle size distribution.
The Nano Spray Dryer B-90 is BUCHI’s 4th generation lab scale spray dryer and is particularly designed to evaluate spray drying during the early stages of product development.
The dryer has a novel electrostatic particle collector for highest yields of fine particles with modular glass assembly and visible spray process having short set-up times and simple cleaning and sterilization.
The manufacturer claims that only a minimal sample amount of high value product needs to be invested to receive a dry powder, the process adopts an efficient and fast process due to simple assembling, easy cleaning and fast product changes with minimal loss of high value products
Areas of application include nanoparticle suspensions / nanoemulsions, micro and nanoencapsulations / englobing, nanoparticle agglomerations, structural modifications, generation of nanoparticles with high recovery rates and spray drying of aqueous and organic solvent samples.
The latest application trends in pharmaceutical formulation and nanotechnology demonstrate the need for fine particles in small powder quantities and with very high yields.
The modular and flexible glass design makes it easy to spray dry a whole variety of applications and is ideal for feasibility studies in R&D laboratories where only milligrams of powder need to be dried.
See for details: http://www.buchi.com/

Carbon nanotube springs

2011-11-08T05:08:00.000-08:00

Researchers at Stanford University in the US have discovered a highly elastic, transparent thin film that conducts electricity extremely well. The film is made of wavy, spring-like carbon nanotubes.
Making the film
The researchers made the transparent elastic films by airbrushing a solution of carbon nanotubes onto the top and bottom surface of a flat silicone sheet. After coating, the researchers stretched the sheet and made to relax so that the nanotubes naturally formed wavy, spring-like structures. The researchers claim that this is the first stretchable, transparent, skin-like sensor so far made with or without carbon nanotubes.
Working
The set-up behaves like a capacitor, with the silicone layer storing electrical charge. When pressure is applied to the sensor, the silicone layer compresses and alters the amount of electrical charge that it can store. When the composite film is stretched again, the nanotubes straighten out in the direction they are stretched. The film can be stretched up to two and half times its initial length in any direction without damage, always reverting back to its original dimensions, even after many stretches. The electrical conductivity of the thin film does not change as long as the material is not stretched beyond the initial stretch amount.
Applications
This device can be used to restore touch and pressure sensitivity to amputees, injured soldiers and burn victims, and also for applications in robotics and touch-sensitive computer displays. It can be used as the electrode material in "skin-like" pressure, force and stretch sensors. The film might find applications in screens for mobile devices that can sense a range of pressures. Applications also include sensors for touch screens that are collapsible, stretchable and virtually indestructible, transparent electrodes for solar cells that could be wrapped around the curved surfaces of vehicles and buildings without wrinkling, and sensors for robots and artificial intelligence systems.
Other applications include 'smart' steering wheels that could sense if the driver was falling asleep which give 'biofeedback'. Artificial skin made from the material might also be used to restore the sense of touch to amputees when fitted with prosthetic limbs covered with the skin, injured soldiers and burn victims.
The researchers claim that in the future, it should also be possible to use these films to design organic, skin-like devices with the ability to sense moisture, temperature, light and even chemical and biological species. They would also like to integrate the skin-like pressure sensors with neurons, as well as try out the electrodes in solar cells.

Quantum dots improve solar cells

2011-11-02T04:26:00.000-07:00

Solar cell
A solar cell also called photovoltaic cell or photoelectric cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect. Improvements were slow but the only widespread use was in space applications where their power-to-weight ratio was higher than any competing technology.
Photovoltaic cells are made of semiconductors such as silicon. Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material and transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely creating electricity.
Conventional crystalline silicon solar panels are expensive and inefficient. One way to increase the efficiency of solar cells is to use semiconductor nanoparticles, or quantum dots.
Semiconductor quantum dots
Researchers so far had only succeeded in creating such photo excited electron-hole pairs inside quantum dots. This is not very useful for real solar cells in which electron and holes need to be able to move freely throughout the entire sample. Only then can they create an electrical current that can be collected at an electrode.
Researchers at the Delft University of Technology in the Netherlands have shown for the first time that photo excited electrons can move freely in layers of linked semiconductor quantum dots. The new finding will be important for making cheap and efficient solar cells from these materials.
Due to avalanche effect a single photon can excite several electrons at the same time in a sample compared to conventional solar cells which can excites only one electron on incidence of light particle. In theory, the efficiency of cells made from these materials can reach 44%.
Free electron transport
Researchers have shown that electron-hole pairs can move as free charges between dots when these semiconductor nanoparticles are very densely clustered together while remaining separate using small spacer molecules. The arrangement means that the dots. The nanoparticles are so close to each other that in this arrangement every single light particle that is absorbed by the solar cell results in the generation of mobile electrons and holes. Since there are many of these electrons and holes, solar cells made of semiconductor nanoparticles could be very efficient.
The semiconductor nanoparticles behave like atomic crystals when the crystals are brought very close together that the electronic properties of nano crystals films are as good as those of conventional semiconductors. Also the electronic properties can be controlled by controlling the distance between the nano crystals. The researchers say that all the photo excited electrons produced can move freely through the material and that they can be collected in a solar cell. These solar cells can thus be made very simply and have a large photo voltage since energy is not wasted.

Production of graphene

2011-11-01T20:26:00.000-07:00

Graphene
Graphene is a wonder material having incredible properties first discovered at the University of Manchester in 2004. It is an ultra thin form of carbon with a lot of promise applications ranging from ultra fast transistors to DNA sequencing and flexible electronic screens. Graphene was discoed by Andre Geim and Konstantin Novoselov in 2010 for which they were awarded the Nobel Prize for Physics.
Small scale production
A simple technique of making graphene is the "Scotch tape" method of isolating graphene. This involves placing a sample of graphite onto sticky tape and then folding and peeling the tape several times to create progressively thinner layers of graphite eventually leading to a single layer of carbon.
Single-layer graphene can be identified using optical microscope by transferring the graphene to a silicon-based substrate and creating correct contrast to identify thin sheets of carbon. Graphene is the thinnest and strongest material with unusual electrical and optical properties. The electrons in graphene behave as if they are particles of light and do not get scattered.
Large scale production
Researchers at Rutgers University have successfully deposited thin films of chemically derived graphene oxide onto large wafers of silicon to 30 cm size which was previously done on few centimeters size.
Graphene oxide films are transparent and their electrical properties can be tuned from semi conducting to metallic by controlling their thickness. These and other interesting optoelectronic properties could be exploited by fabricating devices on various platforms.
The films produced are highly uniform over large areas and atomically thin. They are deposited by spin coating a concentrated aqueous solution of graphene oxide onto hydroxylated surfaces of Si/SiO2 while controlling the evaporation rate of the solvent used. The films can then be transferred onto any other substrate, or left freestanding. The film thickness can be controlled to vary from 1–2 layers to up to 30 layers, by simply changing the spin-coating speed, graphene oxide concentration or number of deposition cycles.
The films produced are electrically active and field-effect transistors can be made using the films. The material could be used in transparent electrodes for optoelectronic devices, such as solar cells and light-emitting diodes.
Cell growth on graphene oxide
Graphene oxide encourages the proliferation of bacteria and mammalian cells on its surface. Graphene oxide can be exploited in biomedicine and biotechnology to help develop materials and surfaces that could be used to culture human cells for tissue engineering or help produce increased amounts of biopharmaceuticals. If nutrients are included in the culture media on graphene oxide, the cells grow even faster and with higher density compared with cultures without it. In particular bacteria, they tend to form thick biofilms packed with bacteria and extra cellular polymeric substances.
Graphene oxide allows faster and more efficient growth of cells would indeed find many applications in the fields of biomedicine and biotechnology. Graphene oxide could be used to develop materials and surfaces that would be used to culture human cells for tissue engineering or to grow structures that could help heal wounds. This can be deployed in bioreactors to increase the production of biopharmaceuticals or to enhance the production of alternative fuels by organisms specially engineered for these purposes.
Graphene oxide paper
Graphene oxide has been created in to paper that is stiff and extremely strong but can be folded, wrinkled and slightly stretched. Researchers from Northwestern University in the US including Rodney Ruoff have discovered that large quantities of oxidized graphene can be weaved together into create a new type of paper that is stiffer and stronger than other thin materials.
Production
Graphite is oxidized to make graphite oxide leaving roughly half the carbon atoms with an attached oxygen atom, which is then mixed with water where these oxygen atoms repel water molecules, forcing the individual graphene oxide layers to disperse or "exfoliate". The researchers filter this exfoliated mixture through a membrane to collect the layers in such an arrangement to produce graphene oxide paper.
Structure
Normal graphite has a delicate structure, needing only a small lateral force to break apart its regularly-stacked layers, but the layers in graphene oxide paper interweave with one another and wrinkle on larger scales. This allows load to be distributed across the structure, making it stronger than graphite foil and "bucky paper", which is made from carbon nanotubes.
The interwoven structure also lets individual layers shift over each other, so that the collective layers become pliable. The paper can be chemically tuned by altering the amount of oxygen on the layers and by reducing the oxygen content it can be made in to a good conductor. The paper could be infused with polymers, ceramics or metals, to make composite materials that outperform their pure counterparts.
This wide array of properties could mean applications as diverse as membranes with controlled permeability to super capacitors for energy storage. This carbon-based material can be adapted for applications including molecular storage, ion conductors and super capacitors.
Antibacterial paper
Researchers at the Chinese Academy of Sciences have demonstrated that graphene could be used to make antibacterial paper to effectively stop the growth of E. Coli bacteria without being toxic to human cells.
The researchers have found that graphene derivatives, like graphene oxide and reduced graphene oxide, inhibit bacterial growth. Previous studies showed that graphene, and particularly graphene oxide is biocompatible and that biological cells can grow well on graphene substrates. While other nanoparticles, like silver, are well known antibacterial materials, they are often cytotoxic.
Production
The researchers made graphene paper by first synthesizing graphene oxide and reduced graphene oxide in water. This solution was then filtered through paper under vacuum. Freestanding graphene oxide and reduced graphene oxide sheets were then peeled off from the filter paper.
Antibacterial property
The cell membranes of E. Coli bacteria placed on the graphene sheets were severely destroyed. This occurs because graphene enters the endosome of the cell's cytoplasm, pushing it out of the cell. Almost 99% of the cells were destroyed after just two hours in contact with an 85 g/mL solution of graphene oxide at 37 °C. In contrast, the nanosheets were not toxic to mammalian cells under the same conditions.

Analysis of Carbon Nanotubes

2011-11-01T00:08:00.000-07:00

Carbon Nanotubes
Carbon nanotubes have attracted the fancy of many scientists worldwide. The small dimensions, strength and the remarkable physical properties of these structures make them a very unique material with a whole range of promising applications. As the increase of carbon nanotubes in commercial productions, a quick analytical tool for quality verification of the nanotubes becomes more and more important. Diameter, chirality and phonon structure of carbon nanotubes, are related to the mechanical and electrical properties. They can be either metallic or semi conducting, depending on their chirality.
Raman spectroscopy
There are a few microscopy methods to detect and qualify CNT selectively. Transmission Electron Microscopy, Scanning Probe Microscopy, Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM) are widely used to determine the morphology of single CNT particles. Raman spectroscopy has been established as a powerful technique to characterize the structure and electronic properties of carbon nanotubes minimal sample preparation. Raman spectroscopy provides a powerful tool to differentiate between two different sp2 carbon nanostructures (carbon nanotubes and graphene) which have many properties in common and others that differ.
Raman spectroscopy has good spatial resolution (~0.5 micrometers) and sensitivity (single nanotubes) and is rather informative. Consequently, Raman spectroscopy is probably the most popular technique of carbon nanotube characterization. Raman scattering in SWCNTs is resonant.
Similar to photoluminescence mapping, the energy of the excitation light can be scanned in Raman measurements, thus producing Raman maps which contain oval-shaped features uniquely identifying (n, m) indices.
The main features in the Raman spectra of carbon nanotubes are the radial breathing mode (RBM); the disorder-induced D-band, and its corresponding second-order G'-band; and the tangential G-band. The information revealed in Raman spectra provide the important information about the diameter, chirality and phonon structure of carbon nanotubes, which are related to the mechanical and electrical properties.
Analysis modes
Radial Breathing Mode (RBM) is specific to SWNT and usually observed in the region from 150 cm-1 to 300 cm-1. Raman peak position, which is inversely proportional to the tube diameter, of this mode is used to classify the diameter distribution in carbon nanotubes. The G band, a tangential shear mode, corresponds to the stretching mode of the carbon-carbon bond in the graphite plane. The fine structure seen in the G-band depends on tube diameter and chirality. The line shape of the band can be used to help identify metallic and semi conducting nanotubes. The D band is often referred as the disorder or defect band. The D band/ G band ratio is usually used for evaluating the quality of carbon nanotubes.
Visible to NIR laser excited Raman spectroscopy of CNTs are resonance process, which is excitation wavelength dependence of the spectra resulting from the electronic band structure. During the measurement it is important to keep the low laser power to decrease heating effect since Raman shift/shape is dependent on temperature.

Nano properties of Eucalyptus wax

2011-10-31T23:34:00.001-07:00

Eucalyptus
The eucalyptus is cultivated all over the world and leaves from young trees are rounded and blue-green with a silvery bloom, those from mature trees are longer, pointed, tough and glossy green. The leaves are arranged to be most suited to the climate and productive of peculiar effects of light and shade. Nearly all Eucalyptus is evergreen but some tropical species lose their leaves at the end of the dry season. As in other members of the myrtle family, Eucalyptus leaves are covered with oil glands. The copious oils produced are an important feature of the genus. The leaves on a mature eucalyptus plant are waxy or glossy green.
Self-cleaning properties
Researchers of Murdoch University have discovered that a eucalyptus plant native to south west WA has unique self-cleaning and water-repellent properties which could be used for nanotechnology applications. The tree also known as The Rose of the West for its large spectacular flowers, has silvery leaves covered in a wax and produces nano-sized bumps and pillars. This causes water to form droplets to roll over the surface of the leaves and fall towards the root system of the plant, picking up any dirt along the way. These properties, which are known as super hydrophobic and self-cleaning, are similar to the lotus plant's which has inspired a range of self-cleaning and anti-bacterial technologies currently being developed.
Development
An experiment was carried out by the researchers by coating the leaf with carbon black toner from a laser printer cartridge and then observing how the rolling drops of water were able to completely clean the surface of the leaf. The Eucalyptus' waxes gave the leaves remarkable wetting and self-cleaning properties due to surface features.
The team extracted waxes from the leaves and found that they were capable of self-reassembly. When coated on laboratory glass slides, the wax formed features which mimicked the complex three-dimensional geometry of the nano-sized bumps and pillars found on the original leaf surface, making the slide super hydrophobic. It was fairly easy and inexpensive to extract the wax from the leaves and yet the wax still had these remarkable qualities. The added buoyancy support of the wax meant that it was able to carry a greater load than the uncoated slides.
Application
This discovery has the potential to be applied in a variety of ways, from so-called lab-on-a-chip settings in medical research, to the treatment of ships' hulls to help prevent the build up of harmful microorganisms, plants and animals. In micro fluidic devices used in advanced medical research and disease testing, such coatings could help to maintain the sterility of devices which need to be used over and over again.

Carbon MEMS Technology

2011-10-30T08:51:00.000-07:00

Carbon-MEMS (C-MEMS) refers to a microfabrication technique in which photopatterned resists, heat treated (pyrolyzed) at different temperatures in different ambient gases, are used as a carbonaceous structural and functional material for micro electromechanical systems (MEMS). This new material permits an entire new variety of novel MEMS applications that employ structures having a wide variety of shapes, resistivities and mechanical properties. Moreover, carbon surfaces form better electrochemical electrodes and are easier to derivatize with organic molecules than more traditional MEMS materials such as silicon. See (http://www.MEMSuniverse.com )

Nanotube muscle for lab-on-chip

2011-10-30T08:25:00.000-07:00

Lab-on-a-chip
A lab-on-a-chip (LOC) is a device that integrates one or several laboratory functions on a single chip of only millimeters to a few square centimeters in size handling extremely small fluid volumes down to less than pico liters. Lab-on-a-chip devices are a subset of MEMS devices and often called as Micro Total Analysis Systems. For lab-on-chip diagnostics nixing fluids on the micro- and nano-scales is crucial. A lab on a chip uses capillary action to create a potential one-step diagnostic tool, which could ultimately test for a wide range of diseases and viruses.
Simple mixer
Researchers of University of British Columbia in Canada and Hanyang University in Seoul, South Korea have made nanotube torsional muscle-like structures useful in applications like micro fluidic pumps, valve drives and mixers. A plastic paddle attached to the rotating yarns was made by researchers as a simple mixer in its own right. The torsional muscle propels a micro-robot like a flagellum in the same way it propels a bacterium.
Bubble-activated micro pump
Chemists in Taiwan have developed a bubble-activated micro pump that can transport blood on a microchip which will help improve point-of-care disease diagnosis. Although many micro pumps have been developed, most require high temperatures or voltages, which can damage blood cells. Electrochemically activated pumps are known but they alter the pH of blood, harming the cells. Micro pumps provide the pressure that drives fluids through channels in lab-on-a-chip Microsystems. The new design overcomes these limitations by confining the pump's electrolysis reaction to an electrolyte-filled side channel on the chip.

Air-bubble-actuated micropump for on-chip blood transportation

CNT yarn

2011-10-23T04:13:00.001-07:00

Nano-actuators
Nano-actuators and motors will be crucial in future micro machines and are already being employed in zoom lenses for digital cameras and vibration alerts for mobile phones, to name but two examples. Still actuators made on the nanoscale poses a challenge because such conventional devices are too complex to easily downsized, boot and poorly. Available torsional artificial-muscle systems are based on ferroelectrics, shape-memory alloys or conducting organic polymers.
Carbon nanotube muscle
Researchers of University of Wollongong in Australia have made an artificial muscle using carbon nanotube threads. The new structure can twist and turn very quickly compared to previously made devices. The muscles are composed of thin carbon nanotube threads. Carbon nanotubes are hollow cylinders of rolled up carbon. For making the torsional structures the carbon nanotubes are to be twisted as they are made into a thread to produces a helical structure of intertwined carbon nanotubes.
Researchers in the US A have made artificial muscle made from carbon nanotubes. The muscles flex when electrically charged and can expand to 220% of their original length in a matter of milliseconds. The devices could find use in medical and aerospace applications, and perhaps even in robots of the future.
Fabrication
Lengths of the nanotube thread are taken, partially immersed in an electrically conducting liquid or electrolyte, both ends of tubes held firmly and one end is connected to a low-voltage battery. When the voltage is applied, the thread absorbs some of the liquid and swells up. The pressure subsequently produced by the swelling causes the twisted structure to partially unwind, creating a rotating action similar to that seen when stretching a helical spring. Thus a twisting motion is observed in the nanotube. The structure can be made to rotate in the opposite direction by decreasing the applied voltage.
Applications
The new muscle-like structures will be important for applications that require mechanical movement and where volume is limited and they could find their way into a host of application areas, including micro fluidics, valves and robotics. By charging the thread with just a few volts of electricity the threads are found strong enough to hold large weights of nearly 2000 times heavier than the thread itself. Carbon nanotubes, which are normally stiff and strong and that have been made more flexible by spinning them into yarns, are ideal for making such muscle-like structures because they have good electrical conductivity. The muscles made by researchers of US A might be used as actuators in medical and other devices, as well as in electrodes for solar cells, light-emitting diodes and displays. They might also find their way into future robot arms and legs.

Stacking layers in graphene

2011-10-21T23:35:00.000-07:00

Graphene

Graphene, a sheet of carbon just one atom thick, is promising for making molecular electronic devices of the future due to its unique electronic, mechanical and thermal properties that include extremely high electrical conductivity and exceptional strength. It is tougher than diamond, but stretches like rubber. It is virtually invisible, conducts electricity and heat better than any copper wire and weighs next to nothing. It could lead to mobile phones high definition televisions as thin as wallpaper, and bent electronic newspapers that readers could fold away into a tiny square. It could transform medicine, and replace silicon as the raw material used to make computer chips. The chemistry of the surface on which graphene is deposited plays a key role in shaping the material’s conductive properties.
Research results show that when deposited on a surface treated with oxygen, graphene exhibits semiconductor properties. When deposited on a material treated with hydrogen, however, graphene exhibits metallic properties.
Graphene stacks
Recently, researchers have also turned their attention to multilayer graphene because they expect it to have even more astonishing characteristics due to enhanced electronic interactions between the layers making up the structure.
Triple layer graphene comes in two types; with different layer stacking orders: ABA and ABC. The difference is that the top layer is shifted by the distance of one carbon atom in the sheet relative to another. In such multilayer systems, the stacking order dramatically affects the electronic properties of the structures. The effect in graphene is expected to be particularly pronounced as ABA-stacked triple layers are predicted to be semi-metals with tunable band overlaps, and ABC-stacked triple layers are predicted to be semiconductors with tunable band gaps. ABA-stacked triple layer graphene is metallic and that ABC-stacked triple layer is insulating where as theory predicts both types of triple layers to be conducting.
The results indicate that ABC triple layer graphene has an intrinsic band gap, which likely comes from the enhanced electronic interactions in this multilayer system. A band gap, however small, is important for making electronic devices from graphene which normally lacks a band gap. The findings suggest that graphene's electronic properties can be tuned, in principle, by simply changing the stacking order of the layers.

Self configurable nanomaterial

2011-10-21T23:09:00.001-07:00

Reconfigurable nanomaterial
As electronic devices are built at very small level they lose their properties and begin to be controlled by quantum mechanical phenomena. To over come this degradation circuits are built into multiple dimensions by stacking components on top of one another.
Researchers at Northwestern University have developed a new nanomaterial with reconfigurable electronic properties so that they can rearrange themselves to meet different computational needs at different times.
Process
This technology allows direct current to flow through a piece of continuous material and streams of electrons can be steered either in multiple directions or in multiple streams flowing in opposing directions at the same time through a block of the material. This has made possible that combines different aspects of silicon- and polymer-based electronics to create nanoparticle-based electronic materials.
According to the researchers the materials besides acting as three-dimensional bridges between existing technologies, its reversible nature could allow a computer to redirect and adapt its own circuitry to what is required at a specific moment in time.
This means that a single device can reconfigure itself into a resistor, a rectifier, a diode and a transistor in response to signals from a computer. The multi-dimensional circuitry could be reconfigured into new electronic circuits using a varied input sequence of electrical pulses.
Hybrid material
The hybrid material is composed of electrically conductive particles, each five nanometers in width and coated with a special positively charged chemical. The particles are surrounded by negatively charged atoms that balance out the positive charges fixed on the particles.
Process of making components
By applying an electrical charge across the material, the small negative atoms can be moved and reconfigured, but the relatively larger positive particles are not able to move.
By moving these negative atoms around the material, regions of low and high conductance can be modulated; the result is the creation of a directed path that allows electrons to flow through the material. Old paths can be erased and new paths created by pushing and pulling the negative atoms between larger, positively charged nanoparticles which are fixed in place. The regions of high and low ionic concentration allow for the material to become either more or less conductive in those areas. By controlling how the ions are distributed, one can control how current flows. More complex electrical components, such as diodes and transistors, can be made when multiple types of nanoparticles are used.
Applications
The development could lead to a computer that can simply reconfigure its internal wiring and become an entirely different device, based on changing needs. A single device can reconfigure itself into a resistor, a rectifier, a diode and a transistor in response to signals from a computer.

Nanobiomaterials application

2011-10-19T19:51:00.000-07:00

Biomolecule-nanoparticle hybrid
Biomolecules, such as proteins (enzymes, antigens, antibodies) or DNA and nanomaterials, such as metal or semiconductor nanoparticles and nanorods have dimensions similar to each other. Hence integration of nanoparticles, with unique electronic, photonic, and catalytic properties, with biomaterials, which display unique recognition, catalytic, and inhibition properties, yields novel hybrid nanobiomaterials of synergetic properties and function. Nanobiomaterials are emerging as the most promising area of research within the area of biological materials science and engineering
Au-NP nanobiomaterials
Biomolecule-nanoparticle hybrid systems are used for bioelectronic applications by the electrical contacting of redox enzymes by means of Au-NPs. The enzymes, glucose oxidase, GOx, and glucose dehydrogenase and GDH are electrically contacted with the electrodes by the reconstitution of the corresponding apo-proteins on flavin adenine dinucleotide (FAD) or pyrroloquinoline quinone (PQQ)-functionalized Au-NPs (1.4 nm) associated with electrodes, respectively.
Similarly, Au-NPs integrated into polyaniline in a micro-rod configuration associated with electrodes provide a high surface area matrix with superior charge transport properties for the effective electrical contacting of GOx with the electrode.
Synthesis of nano gold biomaterials
Synthesis of gold nanoparticle (Au NP) containing both antisense oligonucleotides and synthetic peptides synthesis is accomplished by mixing thiolated oligonucleotides and cysteine-terminated peptides with gold nanoparticles in the presence of salt, which screens interactions between biomolecules, yielding a densely functionalized nanomaterial. Surface loading of each biomolecule can be controlled by controlling the stoichiometry of the components in solution.
Preparation of Au NP–biomolecule conjugates have primarily focused on two classes of materials: homofunctionalized nanoparticles that incorporate one biomolecule functionality, such as DNA, peptides, or antibodies, and heterofunctionalized nanoparticles including conjugates that combine oligonucleotides and antibodies, protein-stabilized DNA-peptide conjugates, alkyl chains and plasmid DNA, or polyethylene glycol and peptides.
Applications
Biomolecule-semiconductor NP hybrid systems are used for the development of photo electrochemical sensors and optoelectronic systems.
Biomolecule-Au-NP hybrids
Biomolecule-Au-NP hybrids use of Au-NPs as carriers for a nucleic acid composed of hemin/G-quadruplex DNAzyme units and a detecting segment complementary to the analyte DNA. The functionalized Au-NPs are employed for the amplified DNA detection, and for the analysis of telomerase activity in cancer cells, using chemiluminescence as a readout signal.
Acetylcholine esterase (AChE)/CdS-NPs immobilized in a monolayer configuration on an electrode can generate photocurrent in the presence of thioacetylcholine as substrate and provides a means to probe the AChE activity.
The association CdS-NP/double-stranded DNA hybrid systems with an Au-electrode, and the intercalation of methylene blue into the double-stranded DNA, generate an organized nanostructure of switchable photo electrochemical functions.
The oxidation of the intercalator yields in the presence of triethanolamine, TEOA, as sacrificial electron donor, an anodic photocurrent by the transport of conduction-band electrons, through intercalator units, to the electrodes, and filling the valance-band holes with electrons supplied by TEOA giving a potential-switchable directions of the photocurrents, and reveal logic gate functions.
Self-cleaning nanobiomaterials
Researchers at Rensselaer Polytechnic Institute in Troy, NY used nanotechnology to design a self-cleaning plastic in which the enzyme molecules are an integral part of the material. When the plastic comes into contact with bacteria or other pathogens, the enzymes attack the microbes and destroy their ability to bind to its surface. Researchers attached enzymes to the surface of large carbon nanotubes which stabilize the enzymes, are then incorporated into a polymer. The technique could work for any number of enzymes including materials that kill specific microbes or even degrade oil sludge on contact. Coatings of the enzyme-polymer material could protect implantable medical devices from scar tissue formation. The unique properties of nanobiomaterials provide advantageous interactions with the proteins that control cellular function. Nanobiomaterials have an increased number of atoms and crystal grains at their surfaces and possess a higher surface area to volume ratio than conventional micro scale biomaterials. These differences in surface topography alter the corresponding surface energy for protein adsorption.
Nanobiomaterials for biosensors
Bionanomaterial research has emerged as a new exciting field, recognized as a new interdisciplinary frontier in the field of life science and material science. Great advances in nanobiochip materials, nanoscale biomimetic materials, nanomotors, nanocomposite materials, interface biomaterials, nanobiosensors, and nano-drug-delivery systems have the enormous prospect in industrial, defense, and clinical medicine applications. Biomolecules assume the very important role in nanoscience and nanotechnology, for example, peptide nucleic acids (PNAs) replace DNA, act as a biomolecular tool/probe in the molecular genetics, diagnostics, cytogenetics, and have enormous potentials in pharmaceutics for the development of biosensors.
Nanobiomaterials as catalyst
Biological macromolecules such as proteins and DNA are versatile supports for organizing nanostructures and catalysts. Catalysts, including biocatalysts, capable of carrying out the multi-electron chemistry needed to produce solar fuels require multiple chemically distinct catalytic centers. These catalytic centers often involve metal ions in paramagnetic states to maximize reactivity and product distribution.
Nanobiomaterials in health care
Biomaterials are used to develop advanced medical devices to improve the course of human life. Nanobiomaterials can be used for human implant, orthopedics, drug delivery, gene therapy, antimicrobial treatments, array technologies, and diagnostics. Nanobiomaterials help with targeting, measuring, sensing, and imaging. They can also help enhance efficiency, safety, quality, and durability.

Nano funnel

2011-10-18T06:50:00.000-07:00

Scientists from the Korea Advanced Institute of Science and Technology in South Korea, the Max Planck Institute of Quantum Optics in Germany and the Georgia State University in USA has managed to concentrate the energy of infrared light pulses with a nano funnel and used the concentrated energy to generate extreme ultraviolet light flashes. These flashes, which repeated 75 million times per second, lasted only a few femto seconds.
Extreme ultraviolet light
Light composing different wavelengths can change frequency by interactions with matter, depending on type and shape of material. Light in the infrared (IR) can be converted to the extreme ultraviolet light by a process known as high-harmonic generation, whereby the atoms are exposed to a strong electric field from the IR laser pulses. These fields have to be as strong as the fields holding the atom together. With these fields electrons can be extracted from the atoms and accelerated with full force back onto the atoms. Upon impact highly energetic radiation in the extreme ultraviolet light is generated. .Due to their short wavelength and potentially short pulse duration reaching into the atto second domain, extreme ultraviolet light pulses are an important tool for the exploration of electron dynamics in atoms, molecules and solids. In order to capture a moving electron, light flashes are needed, which are shorter than the timescale of the motion.
Nano funnel
The researchers have modified light waves with a nano funnel made out of silver and filled with xenon gas to convert femto second laser pulses in the infrared spectral range to femto second light flashes in the extreme ultraviolet.
Process
Light in the infrared (IR) can be converted to the extreme ultraviolet by a process known as high-harmonic generation, by exposing the atoms to a very strong electric field generated by concentrating using a nano funnel. The infrared light pulses were sent into the funnel entrance where they travel through towards the small exit. The electromagnetic forces of the light result in density fluctuations of the electrons on the inside of the funnel. Here, a small patch of the metal surface was positively charged, the next one negative and so on, resulting in new electromagnetic fields on the inside of the funnel, which are called surface plasmon polaritons. The surface plasmon polaritons travel towards the tip of the funnel, where the conical shape of the funnel results in a concentration of their fields.
The funnel acts as an efficient wavelength filter at the small opening only extreme ultraviolet light comes out. With these fields electrons can be extracted from the atoms and accelerated with full force back onto the atoms. Upon impact highly energetic radiation in the extreme ultraviolet is generated. The researchers have created a powerful extreme ultraviolet light source with wavelengths down to 20 nanometers with high repetition rate.
Applications
The new technology can help in the future to measure the movement of electrons with the highest spatial and temporal resolution., and in laser physics to explore the inside of atoms and molecules.

Hot-carrier in Graphene

2011-10-17T04:43:00.000-07:00

Graphene
Graphene is a layer of carbon just one atom thick that has a range of unique electronic, mechanical and optical properties that could have great technological promise. Indeed, since its discovery in 2004.
Photocurrent production
Researchers have created optical devices using graphene. Researchers of Massachusetts Institute of Technology and Harvard University have found hot-carrier regime which is very unusual and is normally only seen at extremely low temperatures or in very non-linear processes, also in graphene it occurs at all temperatures from very low up to room temperature and in the linear regime when the material is excited with a laser. Graphene does not behave like a conventional semiconductor when exposed to light but instead produces hot carriers that generate a photocurrent which is usually driven by an electrostatic potential difference. Such processes form the basis of modern optoelectronics devices. It has been proved that thermoelectric processes could be at play in the material.
Process
According to the researchers, such high values of photocurrent are a result of the photo thermoelectric effect. When you shine a light on graphene, the electrons in the material heat up, and remain hot, while the underlying carbon lattice remains cool, it is these hot electrons that then produce a current. The electrons in the excited graphene cannot cool down easily because they couple poorly to the carbon lattice and so cannot transfer their heat to it
Researchers performed precise spatially resolved optical-excitation microscopy and electron-transport measurements by shining laser light with a wavelength of 850 nm onto the graphene p–n interfaces and measured the photocurrent produced in the devices as the laser spot was scanned over the samples. They found that a strong photocurrent was produced at the p–n contact which increased as the power of the laser beam was increased.
Applications
The finding could be useful for creating new types of ultra fast and highly efficient photo detectors and energy-harvesting devices such as solar cells.

Counting nanoparticles

2011-10-16T12:48:00.000-07:00

Nanoparticles

A nanoparticle is a particle with a diameter that is much smaller than one millionth of a metre and they find widest use in many day to day products. Nanoparticles of a substance behave, quite simply, differently than large particles of the same substance. It is important to determine their size, shape and surface area, in order to improve their properties within various areas of application.
Nanoparticles are not influenced by gravity and thus they do not fall to the bottom of any liquid or gas, but spread and float throughout the space where it is kept. Their area of contact with the surrounding medium is very large due to their small size, which is the reason for many interesting properties.
Nanoparticle sources
There are several sources that result in nanoparticle formation: stationary industrial sources, such as coal fired combustion systems and incinerators; mobile sources, such as automobiles and diesel powered vehicles; and occupational environments, such as those where welding processes are prevalent and those where engineered nanoparticles are deliberately synthesized. There are several natural sources and nanoparticles of biological origin that also need significant attention. For example, pollen fragments are potential causes of allergies, and viral nanoparticles can be used as vaccines or can play a significant role in the spread of disease.
Size distribution analysis
Nanoparticles of a substance can be counted and the size distribution can be determined by dispersing the nanoparticles into a gas. But some nanoparticles tend to aggregate when the surrounding conditions change. Certain types of nanoparticles can even start to aggregate under special conditions to form gel.
Scientists at the University of Gothenburg, Sweden, have reported that it is possible to sort and count the particles, even when they have formed aggregates. The researchers have studied one such aggregating systems, colloidal silica. The gel that forms when salt is added to colloidal silica can be used, for example, to seal rock and to stabilise soil. Nanoparticles that have aggregated can be analysed individually if a colloidal silica gel, which contains these aggregated nanoparticles, is first diluted and then dispersed into the gas phase. If the samples are analysed immediately after being diluted, this method gives an accurate picture of the gel aggregate.
Principle of measurement
Nanoparticles move under Brownian motion and small particles move faster than larger particles. Diffusion Coefficient can be calculated by tracking and analysing the movement of each particle separately but simultaneously. Through application of the Stokes-Einstein equation, particle size can be calculated. Particle concentration/number can also be estimated.
Instrumental methods
In the disk centrifuging method the sample is spun inside a stack of conical disks and components are separated in the space between disks. Individual nanoparticles can be studied under the electron microscope, but this is slow and hardly practical at the routine level and these methods are not successful when the particles to detect are present in small numbers.
Coulter counter method is an indirect method. In this, there is a microscopic aperture in an insulating membrane. An electrical gradient is applied between the two sides of the membrane, which is immersed in a conducting liquid. As the membrane is an insulator, any current can flow only through the aperture, and this current is measured. Now, if there are cells or other particles in the liquid and one of them passes through the aperture, it will effectively block the current path while it is passing through, which would register as a drop in the current. Such changes in current strength are detected and counted to provide data of particle movement. The same principle is used in the nanopore, which can detect much smaller particles like DNA or protein molecules. But while these methods have been useful in the fields where they were developed, they are cumbersome and cannot provide rapid count rates, which is required in many nanoparticle characterisation applications.
Researchers at the University of California, Santa Barbara, reports on improved equipment that can detect and count nanoparticles as small as 10 nm.
NanoSight has developed a unique capability to directly size and visualize nanoscale particles in liquids, with high-resolution, in real-time and with minimal sample preparation. Using nanoparticle tracking analysis (NTA) visualization technique size, count and concentration measurements can be made to give insight into true size distributions even in complex systems.
Izon's qNano utilizes a new non-optical detection principle to enable the size, concentration, dynamics and charge of a wide range of particle types to be measured with high accuracy. Resistive Pulse Sensing combined with Size Tunable Nanopores enables accurate particle-by-particle measurement with representative information on the size and polydispersity of mixtures.
Researchers at Washington University in St. Louis have turned an acoustic phenomenon into a high-resolution nanoparticle detector. Using a ring-shaped micro-laser, the sensor can detect and count individual viruses or synthetic and biological nanoparticles with single particle resolution.
TSI's Scanning Mobility Particle Sizer Spectrometer is a high resolution nanoparticle sizer used for nanoparticle size characterization and the method is independent on the refractive index of the particle or fluid.

Lubricating nanoadditives

2011-10-11T03:59:00.000-07:00

Lubrication is the process of reduce wear and tear of mating materials by interposing a lubricant between two surfaces moving relative to each another. The principle is that lubricants form a physical barrier of thin layer to separate the moving parts.
Lamellar materials of metal disulphide type such as MoS2, WS2, NbS2 etc. are widely used either as solid lubricant for space applications or as additives dispersed in a lubricating base as they have excellent lubricating properties. The most efficient anti-friction additives currently used in the field of the automotive lubrication is the molybdenum dithiocarbamate (MoDtc), in solution in oil, but has problems of toxicity and pollution such as sulphur gas emissions produced by MoDtc and are extremely harmful for the environment. But the tribological performance of common lubricants can be altered by adding small amounts of nanoparticles which provide reduced wear and low friction.
Nano lubricants
Nanostructures such as nanotubes, onions, fullerenes are used as additive of lubrication in a lubricating base due to their spectacular tribological performance and hence serve as a substitute to conventional additives. The nanomaterial such as carbon nanotubes, carbon onions, inorganic fullerenes of MoS2, WS2 offer a strong reduction of the friction coefficient from 50 to 70%, according to the type of nanomaterial, the concentration in particles and the contact pressure compared to those without addition of particles. The reduction of friction of the MS2 type fullerenes are due to progressive delamination, release of MS2 layers in the contact zone and layers forming a tribofilm on the rubbing surfaces.
Examples of nano lubricant additives
Grease containing 10% Cu nanoparticles produced the highest surface quality and the lowest tool wear. NiMoO2S2 nanoparticles and also copper nanopowder as an additive in SAE 30 motor oil effectively reduces friction at high loads and high sliding speeds.
Surface-modified Pd nanoparticles offer stable dispersions in lubricant oils with excellent tribological properties.
Nanoparticle impregnated polymer or metal coatings provide antifriction properties in porous metal parts and used to make self-lubricating components.
C60 and C70 fullerenes have good tribological properties. Spherical fullerenes function as nanoscale ball bearing with the addition of small amounts of quasi-spherical WS2 or MoS2 nanoparticles.
Carbon onion layer compounded with gold dispersion exhibit a low-friction property.
Spherical and cylindrical CeF3 and TiO2 nanoparticles as lubricant additives dispersed in organic solvent in liquid paraffin have excellent load-carrying capacity, good extreme pressure and friction reducing properties.
Graphite nanosheets and WS2 nanorods added to liquid paraffin provide excellent friction reducing properties.

Nanopillars for devices

2011-10-11T02:48:00.000-07:00

A nanopillar can be considered as semi conducting material patterned, by using electron beam lithography and dry etching, into a three-dimensional cylinder with diameter less than 100 nm. In general, epitaxially grown super lattice or multiple quantum well structures are used as the ‘substrate’ material for these nanopillars. Using electron beam lithography and reactive ion etching techniques, low dimensional nanopillar structures can be formed.
Nanoscale transistor, optical chips, biosensors, micro fluidics and micro mirror chips are limited by photolithography, specifically, light wavelengths and electron beam lithography (e-beam litho) cannot expose an entire chip at once.
Nanopillar collapse
When lithography processes was done it was necessary to prevent nanopillar collapse at the 10nm level, but the collapse phenomenon has helped researchers to find a new application. Researchers from MIT's Research Laboratory of Electronics and Singapore's Engineering Agency for Science, Technology and Research have developed a new technique that could produce 10nm chip features using plastic pillar deposition and predetermined pillar collapses.
Process
Etching a pillar into the resist by focusing an e-beam on a single spot, scattering sparse pillars across the chip and allowing them to collapse into more complex patterns could increase e-beam lithography efficiency.
The layer of resist deposited in e-beam lithography is so thin that, after the unexposed resist has been washed away, the fluid that naturally remains behind is enough to submerge the pillars. As the fluid evaporates and the pillars emerge, the surface tension of the fluid remaining between the pillars causes them to collapse.
Collapse control
Researchers from Lanzhou University in China showed how two pillars will collapse toward each other if they are very close. Also by controlling the shape of isolated pillars, they can be made to collapse in whatever direction they are chosen.
Slightly flattening one side of the pillar will cause it to collapse in the opposite direction and partially flattened pillars collapse in the intended direction with about 98% reliability, which is a good "starting point" to build toward industrial yields. The controlled collapse of structures on the micrometer scale has been in use to produce materials with novel optical properties for several years.

Nanofluids to cool computer chips

2011-10-10T11:58:00.000-07:00

Nanofluids are suspensions of nanoparticles in a pure liquid for enhancement of single-phase and two-phase heat transfer. The nanoparticles are typically made of ceramic material, such as alumina or silica, but can be of other materials, diamond, nanoparticles of metals, oxides, carbides, nitrides, or nanotubes.
Nanofluids exhibit enhanced thermal properties such as higher thermal conductivity, heat transfer coefficients, magnetic pumping applications and capillary properties compared to the conventional base fluids. As a cooling fluid, nanofluid can provide considerable cooling in any cooling system. Hence, there is considerable interest in the use of nanofluids for any process that uses process heat requiring cooling.
Certain nanofluids can be made to conduct heat extremely well when a magnetic field is applied to them. This phenomenon can be used to cool down miniature devices like micro- and nano-electromechanical systems, and computer chips.
Researchers at the Indira Gandhi Centre for Atomic Research in Tamilnadu, India have developed novel nanofluids which could be ideal coolants for future electronic devices due to large thermal conductivities.
The materials studied by the researchers are a colloidal suspension of single-domain super paramagnetic Fe3O4 nanoparticles between 3 and 10 nm in size that are magnetically polarizable responding to a weak magnetic field. The particles are capped with a monolayer of surfactant molecules so that they do not agglomerate.
Principle
In any particles the magnetic moments are oriented in random directions, but when a magnetic field is applied, the particles align in the direction of the field and overcome the thermal energy of the particles due to the magnetic dipolar interaction energy depending on the distance between neighboring particles and their mutual orientation. As soon as the dipolar interaction becomes sufficiently strong, the magnetic particles form a chain-like structure as they line up in the direction of the applied field. The thermal conductivity of the nanofluid then increases because heat can then flow very efficiently along the chain.
The increase in the thermal conductivity in these fluids is several hundred times that of traditional nanofluids and is perfectly reversible using which it can be tuned from high to low values by applying the magnetic field either parallel to the direction of particle chains or perpendicular to them. These properties mean that the nanofluids could be ideal for use as "intelligent" coolants according to the researchers.
By incorporating a feedback control circuit in a device, it can automatically sense and vary the magnetic field strength depending on the amount of cooling needed in components such as computer chips or MEMS and NEMS devices.
Liquids embedded with nanoparticles have high stability when exposed to electric fields and this property can lead to new types of miniature camera lenses, cell phone displays, micro scale and nanoscale actuator device applications, fluidic devices, digital display devices, optical devices and micro electromechanical systems (MEMS) such as lab-on-chip analysis systems.
Since the boiling characteristics in pool boiling are similar to flow boiling, nanofluids have opened up exciting possibilities of raising chip power in electronic components or simplifying cooling requirements for space applications. Further nanofluid pool boiling is transient and has shown that this is due to the growth of the nano coating over the heated surface during the course of the pool boiling.

Nanoscoops for battery anode

2011-10-03T04:17:00.000-07:00

Charging a cell phone or laptop could take minutes instead of hours, due to the development of a new nanomaterial for battery electrode. The material is made up of what is called nanoscoops containing "cones" of carbon and aluminum with "scoops" of silicon on top. These nanoscoops would replace the graphite anode used in today's lithium-ion batteries, which are the most common type of batteries found in consumer electronics.
Lithium-ion batteries
Lithium-ion batteries are used in cell phone, laptop or other devices. The problem with today's lithium-ion batteries is that they must be charged and discharged slowly to prevent the anode of battery from falling apart when done at a fast rate. This is because inside the battery, lithium ions move in and out of the anode, causing the negatively charged electrode to change in its volume putting stress on the anode and, over time, this stress accumulates to the point where the anode stops working. If the charge and discharge is done very slowly then the stress buildup is not that serious a problem, but if it is done too quickly then the stress builds to an extent that the battery gets damaged.
Anode from nanomaterials
To address this problem, the Researchers of Rensselaer Polytechnic Institute (RPI) in New York have developed a new anode made from nano materials and have made a button cell Li-ion battery with a nanoscoop anode which can charge 40 to 60 times faster than a typical Li-ion battery which would be useful in electric cars to accelerate after stopping.
Since nanomaterials have very flexible structures they have been tried in the past. They show some improvement but do not have the quick charge-discharge time exhibited by the nanoscoops.
Instead of just one nanomaterial, the researchers created a layered structure of carbon nanorods coated with a thin layer of aluminum and topped with a scoop of silicon. Each layer acts as a sort of "stress absorber" for the next layer, reducing the overall stress felt by each individual material and resulting in an improved anode. Because a gradient in strain is developed the structure can not peel off or break off the substrate.
The amount of charge stored in a Li-ion battery is directly related to the mass of the electrode. And because these nanoscoops are so light, necessary mass can be obtained either by growing longer nanoscoops to possibly increase the length from its current 170 nanometers to a few microns or by creating more layers of nanoscoops.

Auger electron spectrometry (AES)

2011-10-02T12:10:00.000-07:00

Auger electron spectrometry is a surface sensitive analytical technique used mainly to determine the elemental composition of materials and, in certain cases to identify the chemical states of surface atoms. AES is a popular technique for determining the composition of the top few layers of a surface. It cannot detect hydrogen or helium, but is sensitive to all other elements, being most sensitive to the low atomic number elements.
Auger electron spectrometry is named after Pierre Auger who investigated this process during 1923. The information depth for Auger analysis is the top 0.5…5 nm of the sample, and can be used in depth profiling applications in conjunction with ion beam sputtering.
Principle of AES
In this method the sample is irradiated by a primary electron beam, where in all elements with Z ≥ 3 (Li) emit Auger electrons by a process called Auger process. The energy distribution of the electrons emitted from the sample is analyzed in a spectrometer.
The Auger electrons, when analyzed as a function of energy, are used to identify the elements and at lower chemical states. The sensitivity for the elements varies over the periodic table; using Auger electrons the detection limit is about ≤ 1 %.
Electrons of energy 3-20keV are incident upon a conducting sample causing ejection of the core electrons from atoms contained in the sample resulting in a photoelectron and an atom with a core hole. The atom then relaxes via electrons with a lower binding energy dropping into the core hole. The energy thus released is converted into an X-ray or made to emit an electron called an Auger electron after which the atom is left in a doubly ionized state. The energy of the Auger electron is characteristic of the element that emitted it, and is used to identify the element. The short inelastic mean free path (IMFP) of Auger electrons in solids ensures the surface sensitivity of AES.
Conditions
Auger electron spectrometry is a destructive technique. AES technique is used in combination with sputter cleaning and is carried out in UHV conditions. Normally, when a sample is brought into the UHV environment from air, it will be coated with carbon and oxygen which is removed usually by sputtering process before the clean surface is investigated. Sputtering is carried out by directing a beam of Ar ions at between 500eV and 5keV at the sample. This process cleans the surface, but can also be used to erode away the sample to reveal structure beneath the surface.

Novel applications of quantum dots

2011-09-29T01:08:00.000-07:00

Nanoparticles, nanorods or nanofibres and nanofilms have properties that are normally different from those of the corresponding bulk material.
Semiconductors
A semi conductor has electrical conductivity in between an insulator and a conductor. Electrons have to be shifted into the conduction band from the valence band by supplying appropriate amount of energy called the band gap to be absorbed by the material.
Semiconductor quantum dots
Semiconductor quantum dots (QDs) are nanoparticles or nanorods made of a semiconductor material which has unique properties. But the QDs combine their semiconductor properties with valance and conduction bands in a semiconductor. If the band gap falls in the visible region, then the QD solutions made with particles of different dimensions may show different colors. QDs which do not absorb/emit light in the visible region do not show any color in solution; their energy emissions fall in the ultraviolet or infrared regions of the spectrum. Because of their unique properties, they can be used in many fields, such as medicine and electronics.
Tailoring QD properties
The control of their dimensions of QDs is obtained using capping agents such as molecules, generally organic ligands, which stop the growth of the nanoparticles, stabilize them and prevent aggregation/agglomeration of the particles themselves.
Further the capping agents can also be used to tune the properties of QDs. By employing a ligand with particular reactivity, QDs can chemically interact with their surroundings. For example, if the capping agent is a long organic chain, the QDs will be hydrophobic, while the use of a polar ligand will make them hydrophilic, thus getting QDs made of the same material but with a different reactivity.
Applications
QDs are currently employed in biology, to detect some particular types of cells. QDs prepared with bioconjugate molecules can be bonded selectively to some cells such as cancer cells or to some harmful bacteria such as E. coli as capping agents. Sample can be treated with QDs and they will show a colored/fluorescent signal when bonded to such molecules or bacteria indicating their presence. This application will help to diagnose a disease, or to establish a possible contamination with dangerous bacterial strains.
QDs are used in fields such as solar cells ito ncrease efficiency of the cell in converting light into energy and also in optoelectronics. CdS or CdTeS QDs can be the used with TiO2 nanowires with a reported efficiency increase of 300% and 350% for CdS and CdTeS respectively. QDs are used for generation of Light Emitting Diodes (LEDs) giving energy-efficiency and also producing brighter colors.
Market
Recent developments in the QD have created a potential market. In the past the commercial use of QDs was limited due to their high cost, but due to the novel discoveries and investments in sectors such as solar energy and optoelectronics the cost of QDs has reduced and the field of application has become wider.

Doped nanotubes

2011-09-22T06:50:00.000-07:00

Fast growing doped nanotubes
US researchers have doped and grown carbon nanotubes in a controlled way by regulating the amount of active nitrogen-doping species. This finding makes possible to tune the electronic character of these nanostructures. The researchers have chosen the best precursor for an efficient yield and found that hydrogen cyanide (HCN) whose structure is similar to that of C2H2, is the active precursor responsible for doping the nanotubes with nitrogen. The team was able to measure dopant concentrations down to as low as 10–5 atomic percent nitrogen in the nanotube lattice which allowed seeing potential dopants at the levels employed when making practical doped devices.
Super growth method
The researchers made aligned single-walled carbon nanotubes using an ultra thin catalytic layer of 0.5 nm of iron using a "super growth" method. Here, the nanotubes usually self-assemble into vertically oriented structures upwards faster from the catalyst layer, which itself remains on the base of the growth substrate due to a small amount of water vapour present during the process.
The idea of conventional super growth was combined with a precursor that decomposed into an active molecule with an N-C triple bond, and as the carbon is incorporated into the lattice, the nitrogen gets scooped up into the growing nanotube as well. Nitrogen going into the tubes was controlled by simply regulating the amount of the precursor.
Applications
The N-doped nanotubes might be used to build more conductive structures for energy storage devices such as super capacitors or highly conducting lightweight wires of nanotubes, energy-harvesting or conductive armour applications and develop 1D nano templates using doping as a 'knob' for controlled functionalization of nanotubes. Such components will have wide applications in space science.
High conductivity
The N-doped nanotubes are more conducting than their undoped counterparts because the dopant shifts the Fermi level in these semiconductor materials into the conduction band. This property could be exploited to make tubes that have varying Fermi levels from one end to the other by modulating the amount of N along their lengths. This means that the nanotubes would then have different conductivities along their lengths. Such a concept is at the heart of bottom-up nanomaterials engineering.
High yield
A research team at the Chinese Academy of Sciences in Beijing has produced high yields of semi conducting CNTs by a method, where the CNTs were doped with boron and nitrogen. The doping introduced a semiconductor band gap, so that the top electrons in the nanotube had slightly lower energy than that required for conducting electricity. When boron and nitrogen were added together, they replaced neighboring pairs of carbon atoms in the lattice, producing samples in which over 97% of the nanotubes were semi conducting.
Electrodes
Researchers from the University of Dayton have found that aligned nitrogen-containing carbon nanotubes can act as an efficient metal-free electrode in a fuel cell. They can successfully replace existing platinum-based catalysts, having a much better electrocatalytic activity and long-term operation stability. CO impurities in the hydrogen do not affect electrodes, the crossover effect is reduced to a minimum and the cost of fuel cells is briought down.
Fluorescing nanotubes
Using a chemical vapor-deposition technique, a research team from Pennsylvania State University in University Park and the Center for Applied Energy Research in Lexington, Ky., has fabricated ruthenium-doped multiwall carbon nanotubes that photoluminesce at 515 nm.
The researchers believe that the method may be applied to other transition-metal and rare-earth elements to produce different frequencies of luminescence, potentially leading to display applications with pixel sizes down to 10 nm.
Field-effect transistors
The doped nanotubes might be used to build field-effect transistors with excellent switching ability, producing an ‘ON’ current of around a million times higher than the ‘OFF’ current. This could open the way to complex integrated circuits of assorted nanotube devices.
Hydrogen storage
By making doped carbon nanotubes with transition metals and alloys a weak covalent bond similar to cases of dihydrogen bond that is not restricted to pure physisorption or chemisorption bond can be produced. It is possible to enhance and tune the hydrogen storage capabilities of the nanotubes due to the introduction of transition metals and hydrogen bonding clusters into the nanotubes.
Doped nanotube cables
Iodine-doped, double-walled nanotube cables have very low electrical resistivity due to the low density and high specific conductivity. Such doped nanotube cables can replace metal wires in a household circuit and find a range of applications, from low dimensional interconnects to transmission lines.

Organic Nanofertilizer video

2011-09-20T11:52:00.000-07:00

NANOTECHNOLOGY PRODUCTS video

2011-09-20T11:34:00.000-07:00

Extending the life of furniture, clothes, bags, shoes, protection against stains from everyday use and accidents and ideal for office spaces with leather furniture all possible with nanotechnology. See the video.

Shiny rims even after an off road trip through nature is also possible thanks to iCover Car Rim. Mud, water, brake pad dust and dirt are quickly repelled from the rims surface without having the chance to create stains. Even the most difficult of grime that may accumulate on the surface of the rims can be easily removed with a simple wash, no specialized harsh cleaning chemicals required.

Nanotechnology Video

2011-09-20T11:30:00.000-07:00

Nanotechnology, is the study of the controlling of matter on an atomic and molecular scale. Generally nanotechnology deals with structures sized between 1 to 100 nanometer in at least one dimension, and involves developing materials or devices within that size. See the video on introduction to nanotechnology.

Nanotech news

2011-09-18T09:42:00.000-07:00

Nanorods made of fullerenes improve performance of polymer solar cells

The biggest obstacle to making use of solar energy has been the excessively high price of solar cells made of inorganic semiconductors. In contrast, solar cells based on semiconducting polymers are affordable, light, thin, and flexible -- but their performance has been lacking. A team led by Chain-Shu Hsu at the National Chaio Tung University and Yuh-Lin Wang at Academia Sinica in Taiwan has now developed a new approach that uses fullerene nanorods to significantly increase the effectiveness of polymer-based solar cells. They introduce their work in the journal Angewandte Chemie.

Forces within molecules can strengthen extra-long carbon-carbon bonds

The strength of a chemical bond between atoms is the fundamental basis for a molecule’s stability and reactivity. Tuning the strength and accessibility of the bond can dramatically change a molecule’s properties. For example, a bond’s strength is directly related to its length: stretching a bond beyond its normal length makes it weaker. (PhysOrg.com)

Hot nickel nudges graphene: Study simplifies manufacture of semiconducting bilayer graphene

By heating metal to make graphene, Rice University researchers may warm the hearts of high-tech electronics manufacturers.(PhysOrg.com)

Researchers create nanoscale gold coating with largest-ever superlattice

Researchers at Rensselaer Polytechnic Institute developed a new method for creating a layer of gold nanoparticles that measures only billionths of a meter thick. These self-assembling gold coatings with features measuring less than 10 nanometers could hold important implications for nanoelectronics manufacturing.(PhysOrg.com)

Inside story: Chemical reactivity on the inner surface of single-walled carbon nanotubes

Historically, the interior surface of single-walled carbon nanotubes (SWNTs) has not been considered to be chemically reactive. Recently, however, researchers at the University of Nottingham School of Chemistry in the UK and the Ulm University Transmission Electron Microscopy Group in Germany demonstrated sidewall (inner surface) chemical reactions when they inserted catalytically active atoms of rhenium metal (Re) into these atomically thin cylinders of carbon. These reactions formed nanometer-sized hollow protrusions in three distinct phases (sidewall deformation and rupture, open nanoprotrusion formation, and stable closed nanoprotrusion) which the researchers imaged at the atomic level – in real time at room temperature – using Aberration-Corrected High-Resolution Transmission Electron Microscopy (AC-HRTEM).(PhysOrg.com)

Nano-lubes

2011-09-11T11:30:00.000-07:00

Lubrication

Lubrication is the process of interposing a substance called lubricant between two moving surfaces relative to each another in order to reduce wear of one or both in close proximity in order to allow the surfaces to carry the imposed load and the resulting pressure generated between the opposing surfaces. The interposed lubricant film can be a solid such as graphite, MoS2 or solid/liquid dispersion, a liquid or liquid-liquid dispersion or exceptionally a gas.

Lubricants

Typically lubricants contain 90% base oil such as petroleum fractions called mineral oils and less than 10% additives. Vegetable oils or synthetic liquids such as hydrogenated polyolefins, esters, silicones, fluorocarbons and many others are sometimes used as base oils. Additives act to reduced friction and wear. The most common lubricants form a physical barrier of thin layer of lubricant to separate the moving parts. The tribological performance of common lubricants can be altered by adding small amounts of nanoparticles which provide reduced wear and low friction. Modification of conventional lubricants by adding various additives for different situations is discussed below. But one of the main difficulties of using nanoparticles as additives is their dispersion or dissolution in lubricant oils, typically of hydrocarbon nature. With the surface modification of nanoparticles through long chain high molecular weight hydrocarbons, stable dispersions in lubricant oils become feasible. Nano-lubes may reduce the frequency of oil changes and increase the value proposition of condition-based maintenance practices. Numerous studies have shown that different nanoparticles, impregnated into metal, polymer, ceramic and other coatings, can provide these materials with enhanced tribological performance.
Cu nanoparticles

Lubrication is a key issue in diamond turning of reaction-bonded SiC hard materials. The type and concentration of dispersed nanoparticles significantly affected lubricating performance. Grease containing 10% Cu nanoparticles produced the highest surface quality and the lowest tool wear. Lubrication is because nanoparticle-induced solid lubricating film is formed at the tool-workpiece interface. Also copper nanopowder as an additive in SAE 30 motor oil effectively reduces friction at high loads and high sliding speeds.

Pd nanoparticles

Using surface-modified Pd nanoparticles with tetraalkylammonium chains, stable dispersions in lubricant oils become feasible with excellent tribological properties. The use of these nanoparticles decreases the electrical resistance of the contact up to 99% in comparison with the base oil alone. This outstanding performance is attributed to a combination of factors as metallic character of palladium, nanometric size, and replenishment of Pd nanoparticles onto the contact forming a transfer layer.

Function of nano-lubes

In severe conditions, ordinary lubes can be squeezed out from between contact areas. Adding nanoparticles to the oil can reduce friction and wear rates, and increase load-bearing capacity. Nanoparticles also can be impregnated into polymer or metal coatings to provide antifriction properties, and into porous metal parts to make self-lubricating components. Impregnating does not sacrifice the mechanical properties of the base part. Maintenance-free solid lubricants are particularly suited to ultra-clean environments.

Nanotechnology-based extreme-pressure and anti-wear additives are found to have high chemical and physical stability, even under extreme conditions leading to longer equipment operation life, increased machine performance efficiency, extended maintenance intervals, reduced noise, heat and vibration, reduced energy consumption and decreased air pollution. This is due to improved coverage even on rough surfaces as the nanoscale particles infiltrate even the tiniest spaces between contacting surfaces.

Fullerenes

C60 and C70 fullerenes have a good tribological properties. the nearly spherical fullerenes might behave as nanoscale ball bearings by entering into crevices or valleys and separate the asperities of the mating metal surfaces. The addition of small amounts of quasi-spherical WS2 or MoS2 nanoparticles with fullerene-like structure to various kinds of lubricant greatly improves their tribol-ogical characteristics. Nanoparticles are capable of withstanding a severe hydrostatic pressure, caused by compression. The inner layers of these nanoparticles seem to remain intact. The broken outer layers are expected to be transferred to friction surfaces, providing superior tribological properties of rubbed surfaces.

Carbon onion

Japanese researchers formed carbon onion layer compounded with gold by dispersing carbon onions on a silicon wafer coated with gold. The carbon onion layer compounded with gold has kept lower-friction coefficient for a longer time than gold layer in a certain range of gold film thicknesses and normal forces. in addition, carbon onion layer on a self-assembled monolayer exhibited the low-friction property under a wide range of normal forces.

Molybdenum-Sulfur compounds

Molybdenum disulfide is used as a dry lubricant in, e.g. greases, dispersions, friction materials and bonded coatings. Molybdenum-sulfur complexes may be used in suspension but more commonly dissolved in lubricating oils at concentrations of a few percent. Molybdenum disulfide, MoS2, the most common natural form of molybdenum, is extracted from the ore and then purified for direct use in lubrication. Since molybdenum disulfide is of geothermal origin, it has the durability to withstand heat and pressure. This is particularly so if small amounts of sulfur are available to react with iron and provide a sulfide layer which is compatible with MoS2 in maintaining the lubricating film.

A combination of molybdate and water soluble sulfides can provide both lubrication and corrosion inhibition in cutting fluids and metal forming materials. Oil soluble molybdenum-sulfur compounds, such as thiophosphates and thiocarbamates, provide protection against wear, oxidation and corrosion.
Other nanoparticles

TiO2 nanoparticles as lubricant additives can be dispersed in organic solvent in liquid paraffin. TiO2 nanoparticles have excellent load-carrying capacity, good extreme pressure and friction reducing properties.

Graphite nanosheets and WS2 nanorods, which form a physical deposition film on the rubbing surface whenadded to liquid paraffin provide excellent AW and frictionreducing properties.

CeF3 nanoparticles are spherical and cylindrical have excellent extreme-pressure and friction-reducing properties whenadded to liquid paraffin.

NiMoO2S2 nanoparticles have very favorable anti-frictional properties both as an additive in lubricating oils at room temperature and as a solid lubricant at high.

Commercial products

ApNano Materials manufactures a nanoparticle-based solid lubricant and additive that’s depicted as the rolling of billions of miniature ball bearings. The company has already launched NanoLub, the world's first commercial solid lubricant based on spherical inorganic nanoparticles. ApNano claims that NanoLub reduces friction and wear significantly better than conventional lubricants especially at high loads, prolongs device service life, and lowers maintenance costs and downtimes.

Fullerene peapods

2011-09-10T05:40:00.000-07:00

Peapods

Single-wall carbon nanotubes (SWNTs) have attracted considerable interest after the discovery of C60. Single walled carbon nanotubes provide an empty space isolated from outside conditions. This large internal space can be filled with different structures and molecules can be introduced by de-capping. Fullerenes are most favorable molecules for encapsulation because of their fit diameters. Such single-wall carbon nanotubes encapsulating fullerenes are called fullerene peapods.

The physical properties of such solids are strongly depending on a network dimensionality. Since fullerene-peapods have mixed network dimensionality, they have very interesting physical properties. Usually they are synthesized by using diameter-selected nanotubes as pods. High resolution transmission electron microscopy studies reveal that high-density fullerene chains inside nanotubes fill up to 60% of C60 molecules in a macroscopic average.

A Japanese team has reported that they have filled nanotubes with metallofullerenes--pure carbon spheres enclosing metal atoms--hoping for a new way to control nanotube properties. This work demonstrated a new way to exploit the open space in the tubes and possibly gain more control over their properties.

Nagoya University researchers placed C82 buckyballs containing gadolinium atoms inside nanotubes which changed the electronic structure of buckyballs.

Encapsulation

Several molecules such as fullerenes, endohedral metallofullerenes or alkali halides have been successfully inserted into the interior of SWCNTs. The inside filled structures can alter or enhance the mechanical and electronic properties of the SWCNTs or may allow the fine tuning of these parameters when treated at relatively high temperatures. Researchers of University of Ulm in Germany trapped single atoms of the heavy metal dysprosium within hollow fullerene spheres made up of 82 carbon atoms, and enclosed a series of these dysprosium-seeded cages within single-walled carbon nanotubes, with the fullerenes stringing them along the nanotube forming peapod.

Synthesis

The most studied structure inside SWCNT is the C60 fullerene. The resulting material is called a C60 peapod. The filling is performed by mixing of C60 and SWCNT. The mixture is subsequently evacuated and heated above the sublimation point of C60 for several days. The peapod synthesis requires the heat treatment of SWCNT and fullerenes are sealed together under vacuum, but this method can not be adopted for large scale production purposes. Also for the peapods production, unknown fullerenes are the most undesirable impurities.

To get rid of unknown fullerene from SWNTs in one typical production process, soot is heated in vacuum and then the fullerene free soot is refluxed in H2O2 water solution to remove amorphous carbon particles. Finally, the purified SWNTs are formed to thin black paper and then dried in vacuum. Since the oxidation treatment destroys caps of SWNTs and HCl treatment increases defects on the wall, the purified SWNTs already have sufficient number of entrances for fullerenes.

A SWNT paper is put in a quartz ampoule with fullerene powder (C60 and C70 powder in 99 % purity as fullerene sources) and the ampoule is evacuated. After drying process, fullerene powder is evaporated and made into a film on the SWNT paper. The ampoule is sealed and heated in a furnace up to 650 °C. After keeping at a temperature for two hours, the ampoule is cooled down to room temperature. The SWNT paper is sonicated in toluene for 1 hour to remove fullerenes coated on SWNTs surface. After filtration a sheet of peapod paper is obtained. Then the peapod paper is heated in vacuum to remove toluene.

Sample preparation

For the low temperature synthesis of fullerene peapods the commercial SWCNT material is prepared by the arc-discharge method and is purified using repeated high temperature air and acid washing treatments. The SWCNT material with low initial purity is purified with a triple repetition of H2O2 refluxing and HCl acid etching. The material is then filtered and degassed in dynamic vacuum.

Two filling methods consistent with the effective tube-end opening side-effect of the SWCNT purification can be adopted. It is possible to fill SWCNT with other fullerenes including metallofullerens and clusterfullerenes. The success of such a filling procedure is related again to the diameter distribution of the starting SWCNT.

Filling methods

Vapor-filling

To fill fullerenes from the vapor phase by vapor-filling involves sealing of the SWCNT material with the fullerene in a quartz ampoule after degassing and keeping at slightly elevated temperature. The resulting material is sonicated in toluene in order to remove non-reacted fullerenes, filtered, and dried from toluene in dynamic vacuum for removing non-reacted fullerene particles without an observable effect on the peapods.

Solvent-filling

Fullerene filling into SWCNT in n-hexane by solvent-filling is achieved with mixing the SWCNT material with n-hexane with C60 or C70. The as-received SWCNT materials have to be dried to keep away from humidity. The dynamic vacuum degassing of the SWCNT is crucial for the solvent-filling as rinsing it in water prevents any further solvent-fillability probably because water enters into the nanotubes. The SWCNT, fullerene and n-hexane mixture is sonicated resulting in the partial dissolution of C60. From the C60 solution, undissolved C60 and SWCNT mixture are then refluxed and filtered bucky-papers are dried in air. C60 which are not encapsulated that covers the bucky-paper are removed with the above mentioned two methods of sonication in toluene or by dynamic vacuum treatment.

Uses

Fullerene peapods can be transformed into a double wall carbon nanotube (DWCNT) structure after high temperature annealing. The fullerenes coalesce into an inner nanotube without affecting electronic properties but significantly enhancing the mechanical properties of the tube system. This enhanced mechanical stability makes DWCNTs promising candidates for applications in future electronics, probe tips for scanning probe microscopy, field emission devices and many more. It has been speculated that such materials, when available in higher spin concentrations, may be fundamental elements of quantum-computing. The transformation of solvent prepared peapod to DWCNT with a yield identical to that from vapor prepared materials can be used for the production of high purity and highly perfect industrial DWCNT. Fullerenes inside nanotubes can be compressed by a heavy pressure so that molecules are enclosed in-between and chemical reactions can be induced by these extreme pressures making the peapods effective autoclaves. Peapods encaging metallo-fullerenes exhibit the bandgap modulation due to the electron transfer from metallofullerenes to carbon nanotubes. Such peapods have been applied to FET with novel device properties.

Fullerenes applications

2011-09-07T09:41:00.000-07:00

Fullerene
Fullerenes find wide application in different fields of science since their discovery in 1985. Their size, hydrophobicity, three-dimensionality and electronic configurations make them an appealing subject in science, engineering and medicinal fields. Their unique physical, chemical and biological properties have yielded promising contributions to the industries and many industrial applications are now being commercialized.
Structure
Fullerenes are cage-structured carbon molecules such as C60, C70, C76, and C84 having a spherical shape with a wide range of sizes and molecular weights. For example the C60 fullerene also known as buckminsterfullerene or Buckyball is a good representative. Buckminsterfullerenes are hard crystals, red by transmission, black by reflection, yellow in film form and have approximately 0.7 nm in diameter. In the fullerene structure, all C sites are equivalent and the bond lengths are 0.14 nm for the double bond and 0.146 nm for the single bond.
Properties
By virtue of their high chemical activity and a broad versatility of chemical reactions their physical and chemical properties may be tuned by the addition of element and molecular species into the fullerene lattice (C59N), within the cage (N at center of C60), or coating the surface of fullerene with transition metals.
Fullerenes and fullerenic black are chemically reactive and can be added to polymer structures to create new copolymers with specific physical and mechanical properties. They can also be added to make composites.

Electrochemical and physical properties of the fullerene family especially C60 can be exploited in various medical fields.
Fullerene is able to fit inside the hydrophobic cavity of HIV proteases, inhibiting the access of substrates to the catalytic site of enzyme. At the same time, if exposed to light, fullerene can produce singlet oxygen in high quantum yields. This action, together with direct electron transfer from excited state of fullerene and DNA bases, can be used to cleave DNA.
Synthesis
Fullerenes, a new form of carbon, were discovered in 1985 in graphite vaporization under inert gas at low pressure. Fullerenes are produced using electric arc discharge or thermal CVD processes.
Originally, fullerenes were produced by the carbon arc method developed at the University of Arizona. Only small quantities of fullerenes can be produced by this method as it encounters problems due to the low yield, non-selective carbon cage formation, associated purification issues and the process is not scalable. In the arc discharge process, fullerenes cannot be produced if hydrogen atoms are present in the reaction gas. But, synthetic methods can produce a single isomer of a desired fullerene, free from impurities of other isomers or fullerenes of different sizes. This route is based on planar polycyclic aromatic hydrocarbon precursor molecules containing the carbon framework required for the formation of the target fullerene cage.
Applications
Fullerenes have many properties different from either diamond or graphite. There are many applications of practical importance of fullerene in a wide range of areas and application-oriented patents span a spectrum of potential commercial applications. They include areas such as IT devices, diagnostics, pharmaceuticals, environmental, and energy industries, Few examples include facial creams, moisturizers, lubrications, trace monitors, electronic circuits, electronic devices, sensors, superconductors, catalysts, optical, polymer composites, high-energy fuels, anticancer anti cancer drug delivery systems using photodynamic therapy, HIV drugs, MRI agents and cosmetics to slow down the aging of human skin.
Other interesting classes of fullerenic or curved-layer carbon, as opposed to graphitic or planar-layer carbon, that can also be found in fullerene-producing systems are nanostructures with tubular, spheroidal, or other shapes and consisting of onion like or nested closed shells and soot particles with considerable curved-layer content.
Medical
The medical applications of fullerenes include antiviral activity, antioxidant activity, powerful photo induced biological activities as a potential scaffold for photodynamic therapy and diagnostic applications. In addition, fullerenes have been used as a carrier for gene and drug delivery systems. Also they are used for serum protein profiling as MELDI material for biomarker discovery
Antioxidant
Fullerenes are powerful antioxidants, reacting readily at a high rate with free radicals. Fullerenes hold great promise in health and personal care applications to prevention of oxidative cell damage or death, as well as in non-physiological applications where oxidation and radical processes such as food spoilage, plastics deterioration, and metal corrosion are to be avoided. Major pharmaceutical companies are exploring the use of fullerenes in controlling the neurological damage of such diseases as Alzheimer's disease and Lou Gehrig's disease (ALS), which are a result of radical damage. Drugs for atherosclerosis, photodynamic therapy, and anti-viral agents are also being developed.
Fullerene derivatives hold great potential as inhibitors of HIV aspartic protease enzyme and in the development of novel anti HIV drugs. Fullerenes are known to behave like a "radical sponge," as they can sponge-up and neutralize 20 or more free radicals per fullerene molecule. They have shown performance 100 times more effective than current leading antioxidants such as Vitamin E.
The antioxidant property is based on the fact that fullerenes possess large amount of conjugated double bonds and low lying lowest unoccupied molecular orbital (LUMO) which can easily take up an electron, making an attack of radical species highly possible. In other words the fullerene can react with many super oxides without being consumed considered as the most efficient radical scavenger or radical sponges.
Further water soluble fullerenes namely fullerenols and malonic acid derivatives of C60 have attracted great attention in the field of neurosciences
Catalyst
As catalyst fullerenes have marked ability to accept and to transfer hydrogen atoms, hydrogenation and hydrodealkylations, they are highly effective in promoting the conversion of methane into higher hydrocarbons and inhibiting coking reactions.
Fullerenes are used in Water purification, bio-hazard protection, singlet oxygen catalysis of organics, in proton exchange membranes for fuel cells, in vehicles to provide enhanced durability, lower heat build-up, and better fuel economy with use of fullerene black/rubber compounds.
Polymer Electronics
Organic Field Effect Transistors (OFETS) and photo detectors performance has also been increased due to the n-type semi conducting properties of fullerenes based on C60, C70 along with C84. Fullerene OFETS fabricated with C84 show greater mobility and stability than C60 or C70. While more work is needed, the world of polymer electronics is opening up for both fullerenes and single-walled carbon nanotubes.

Lubricating nanoparticles

2011-09-02T06:46:00.000-07:00

Lubricating nanoparticle
Lubricants are needed to minimize the amount of friction and wear generated in machinery. In carrying out this function, lubricants need to be situated on the surfaces of metals and other substrates as interactions between lubricants and metal surfaces occur at the molecular level.
Lubricant nano additives
Development of nanoparticle containing lubricants and lubricant additives involves stabilizing basic lubricant additives as anti wear and extreme pressure (EP) agents in carriers such as mineral oil.
These agents are applied as solid coatings or used in mineral oil-based dispersions. Solid coatings will perform well for a time but tend to be worn away due to the presence of sharp asperities. Inorganic-based nanoparticle oil dispersions are not stable, and the lubricant additive readily precipitates out or agglomerates into larger particles that are ineffective. Development of nanoparticles that can exhibit anti wear and EP performance are with current lubricant base stocks and exhibit even more environmentally friendly characteristics.
Commercial package
NanoMech has integrated layered inorganic solid lubricant nanoparticles of molybdenum disulfide with canola oil to form a solid lubricant exhibits lubricity and EP characteristics and is commercially known as NanoGlide.
The organic-inorganic nanoparticle-based package developed by NanoMech can also be readily incorporated into most conventional base stocks used in the preparation of lubricants. The use of canola oil also means that the organic-inorganic nanoparticle-based additive is environmentally friendly and can provide good sustainability. The organic-inorganic nanoparticle based package can be utilized in automotive lubricants, biodegradable lubricants, gear oils for earth movers and heavy machinery,for infrastructure development, naval ships, etc., and for greases and metalworking fluids.
Nanoscale tungsten
Nanoscale tungsten comprising substances such as tungsten disulfide are useful lubricating additives offering reduced costs at higher performance. Such lubricating nanoparticles offer ability to distribute forces more uniformly due to thinner film formation. The unusual characteristic that makes lubricating nanoparticle additives useful is that the particle size is less than the naturally occurring characteristic roughness sizes and so the nanoparticles can enter and buffer (or reside) in crevices, troughs thereby reducing the damaging internal pressures, forces and inefficient thermal effects. These additives can be dispersed in existing or new lubricating formulations and provide an easy way to incorporate the benefits of nanotechnology. Tungsten disulfide, molybdenum disulfide, molybdenum tungsten sulfide and such inorganic or organic nanoparticle composition are useful lubricating additives.
Carbon nano-onion
The carbon nano-onion can be used as lubricating nanoparticle. When used as lubricant additives, carbon nano-onions lead to a strong reduction of both friction and wear, even at low temperature. The lubrication mechanism of the onions is based on the process of rolling and sliding inside the contact area. Most of carbon onions seem to remain intact under friction processes and do not generate graphitic planes in contrast to the previously reported conventional behavior.
Solid lubricant layer
Japanese researchers formed lubricants with carbon onion layers compounded with gold by dispersing carbon onions on a silicon wafer coated with gold. The carbon onion layer compounded with gold has kept lower-friction coefficient for a longer time than gold layer in a certain range of gold film thicknesses and normal forces. In addition, carbon onion layer on a self-assembled monolayer exhibited the low-friction property under a wide range of normal forces.
Denmark researchers used transition-metal dichalcogenides as solid lubricants. Sputtered coatings and stoichiometric coatings perform optimally made with ion bombardment as a post-coating process. Stoichiometric-powder granulates were dispersed in isopropanol and ball-milled to obtain a nanoplatelet suspension. The coating was deposited by electro spraying.
Titania/diamond nanocomposite
Diamond nanoparticles have excellent lubricating ability. The fabrication of TiO2 based matrix composites with dispersed diamond nanoparticles are synthesized by a detonation method. The mixing process utilizing a sol – gel method achieved a homogeneous mixture between the diamond nanoparticles and the TiO2 gel by ball milling and consolidated at high temperature by spark plasma sintering. The dispersed diamond nanoparticles of 1 vol.-% were chemically stable with improved coefficient of friction and wear rate at high consolidating temperature.
Cu nanoparticles
Cu and Cu alloy nanoparticles have exhibited excellent friction reduction and wear resistance properties. The working of nanoparticles as additives in oil to reduce friction and wear can be considered by two viewpoints; as ball bearing mechanism and film forming mechanism. For the ball bearing mechanism, chemical/mechanical reactions do not occur. Recent studies indicate that local overheating in friction may imitate deposition of copper and forming of a thin protective film on the worn surface to reduce the friction and wear.
The Chinese researchers state that mechanism can be that friction shearing force and high pressure at the interface can initiate the disengagement of Cu nanoparticles from their organic modified layers, and then high temperature due to direct contact of two surfaces originates melting of the bare Cu nanoparticles. In addition, due to good wetting property on steel surface, the liquid copper may well wet the friction pairs. Afterwards, it can be smeared on the worn surface by the shearing movement. Consequently, a copper protective film is formed.

C60 and Carbon Nanotubes - video

2011-09-02T06:22:00.000-07:00

This video shows how a sheet of graphite (hexagons) can be modified to make closed cages and tubes. Depending on the way the hexagons are arranged three types of carbon nanotubes are possible: zig-zag, armchair and spiral. Each promises unusual and interesting properties.

Nanomanufacturing - video

2011-09-02T05:13:00.000-07:00

Nanomanufacturing presents how to make and assemble nanostructures—particularly nanotubes, nanowires, and nanoparticles—into devices and materials ranging from transistors to films, fibers, and structural composites.

Biodegradation of carbon nanotubes

2011-09-01T04:20:00.000-07:00

Carbon nanotubes which are composed of thick rolls of graphite and stronger than steel have found use in a variety of applications, including reinforcing plastics, conducting electricity in electronics and as sensitive chemical sensors.
Toxicity
The development and application of such nanomaterials have led to serious concern about their potential toxicity. Consumer related commercial products developed with nanomaterials have attracted concern about their safe use, particularly when placed in contact with human beings and the proper disposal of nanomaterials.
Research reports reveal that the toxicity of carbon nanotubes is controversial. There are some reports that with the growing use of carbon nanotubes, there is an increasing chance of environmental pollution and exposure. For example, carbon nanotubes, if inhaled, can cause respiratory inflammation in a similar manner to asbestos. But identification of a potential safety problem is more complicated because carbon nanotubes have been produced in many different forms. Hence, development of a safe method for decomposing carbon nanotubes is desired, but no such technique is available until now.
Safe decomposition of carbon nanotubes is quite challenging due to the nature of the material such as strongest carbon carbon bonds in carbon nanotubes. Researchers have identified a natural enzyme called horseradish peroxidase (HRP) as a potential candidate to biodegrade carbon nanotubes when used with hydrogen peroxide.
HORSERADISH PEROXIDASE (HRP)
HRP is known to biodegrade different organic compounds, including poly aromatic hydrocarbons that are close in composition to carbon nanotubes. This enzyme is also very robust and works well over a broad range of temperatures according to the researchers. HRP when added to the carboxylated carbon nanotubes in the presence of hydrogen peroxide and incubated for few weeks at low temperature and neutral pH in the dark degrades carbon nanotubes. Electron spin-resonance analysis indicates that the HRP remained viable and was not deactivated by the carbon nanotubes.
The degradation can be attributed to the formation of a highly reactive intermediate. The active site of the HRP is an iron (III) porphyrin ring complex. Oxidation with hydrogen peroxide generates an iron (IV) porphyrin radical cation that decomposes carbon nanotubes by reducing their length.

Applications of tungsten nanoparticles

2011-09-01T03:24:00.001-07:00

Nanoparticles of tungsten, tungsten nanoalloys and nanocompounds find wide application.

Pigments

Nanoparticles comprising tungsten containing multi-metal oxides can be used as pigments. Because they are smaller than the visible wavelengths of light, it leads to visible wavelengths interacting in unusual ways with nanoparticles compared to macro particles. Inorganic pigments ensure homogeneous lattice level mixing of elements in a complex multi-metal formulation. In this context tungsten nanocompounds are ideally suited for creating color and making superior pigments.

Additives

Substances containing nanoscale tungsten such as tungsten disulfide are useful lubricating additives, because they enable thinner films, offering reduced costs and distribute forces more uniformly with higher performance to improve the life or motor or engine. The nanoparticles can enter and buffer or reside in crevices, troughs thereby reducing the internal pressures, forces and inefficient thermal effects. These additives can be dispersed in lubricating formulations. Tungsten disulfide, molybdenum disulfide, molybdenum tungsten sulfide and such inorganic or organic nanoparticle composition can be added as lubricating additives in shaving blades and other surfaces requiring minimization of friction.

Analytical Agent

Sodium tungsten oxide nanoparticles, in high purity form are useful in biochemical analysis. Tungsten nanoparticles in metallic form are useful in the analysis of carbon and sulfur by combustion in an induction furnace. The high surface area of nanoparticles comprising tungsten, with mean particle size less than 100 nanometers make them useful in these applications. Tungsten nanoparticles may also be used to form stronger polymer composites.

Electronic applications

Tungsten nanomaterials offer several unusual benefits as electron emitters as the small size of nanoparticles can enable the formation of very thin film devices, lower the sintering temperatures and sintering times, exhibit inherently low vapor pressure even at high temperatures and have unusual quantum confinement and grain boundary effects enabling the preparation of improved electron emitting devices. they also offer novel compositions for chemical, mechanical polishing applications and electrical contacts. Photocopiers, facsimile machines, laser printers and air cleaners can benefit from charger wires prepared from tungsten comprising nanomaterials. Nanodevices having electrodes, chemical sensors, biomedical sensors, phosphors and anti-static coatings can be prepared from nanoscale powders comprising tungsten. Nanomaterials comprising tungsten are particularly useful as direct heated cathode or heater coils for indirectly heated cathodes in cathode ray tubes, displays, x-ray tubes, X-ray device anodes, klystrons, magnetrons for microwave ovens and electron tubes. Multimetal nanomaterial compositions comprising tungsten include those based on rare earths and thoria for high intensity discharge lamps and welding electrodes. The unusual combination of vapor pressure, electrical conductivity and electronic properties make nanomaterial compositions comprising tungsten useful as substrate for high power semiconductor rectifying devices, high voltage breakers, incandescent lamps such as household lamps, automotive lamps, and reflector lamps for floodlight or projector applications, audio-visual projectors, fiber-optical systems, video camera lights, airport runway markers, photo printers, medical and scientific instruments, and stage or studio systems. High temperature furnace parts such as heating coils, reflectors, thermocouples can also benefit from the quantum confined and low vapor pressure characteristics of tungsten nanomaterials.

Nanomedicine

2011-08-30T11:23:00.000-07:00

A good video to enjoy

Nanomedicine: nanotechnology for cancer treatment

2011-08-30T11:16:00.000-07:00

Nanotechnologies can be used to deliver drugs for safer and more efficient treatment of cancer. See the video

Nanotechnology and food

2011-08-30T11:11:00.000-07:00

See how nanotechnology is used in food science

Nanotechnology, nano engines and more

2011-08-30T11:03:00.000-07:00

Nanotechnology, is the study of the controlling of matter on an atomic and molecular scale.See the video below to understand further in animation mode.

Bio-sample analysis using AFM

2011-08-28T11:44:00.000-07:00

(Photo courtesy:Catholic University of Chile)
Biological samples
AFM can be used for taking images of non-conducting surfaces of biological systems such as for analyzing the crystals of amino acids and organic monolayers, DNA and RNA analysis, protein-nucleic acid complexes, chromosomes, cellular membranes, proteins and peptides, molecular crystals, polymers and biomaterials and ligand-receptor binding. For the analysis bio-samples are investigated on lysine-coated glass and mica substrate, and in buffer solution. By using phase imaging technique one can distinguish the different components of the cell membranes.
Sample treatment
For bioimaging using AFM, sample preparation is simple like spotting a few micro liters of solution on mica or glass by avoiding surface contaminations. Initially the substrate-adsorbate is rinsed with a large excess of buffer followed by dialysis, centrifugation and homogenization. The samples are stabilized by adding covalent cross-linking agents or certain cations capable of linking the constituents of the sample to each other or to the substrate to get good contrast and to reduce mechanical damage.
Imaging of nucleic acids
Nanometer-resolved images of unmodified nucleic acids, chromosome mapping, transcription, translation and small molecule-DNA interactions such as intercalating mutagens need high-resolution studies and for such purposes highly reproducible images can be obtained using AFM. Very clear resolution of nucleic acids are needed to control of the local imaging environment including sample modification, to adopt tapping mode scanning techniques, to develop improved AFM probes such as standard silicon nitride probes modified by electron beam deposition and oxide sharpened nanoprobes and compatible substrates such as salinized mica and carbon coated mica.
Cell studies
AFM can be used to study the dynamic behavior of living and fixed cells such as red and white blood cells, bacteria, platelets, cardiac myocytes, living renal epithelial cells, and glial cells up to a resolution of only 20-50 nm, but not sufficient for resolving membrane proteins but still suitable for imaging other surface features, such as rearrangements of plasma membrane or movement of sub membrane filament bundles.
Study of small molecules
There has been recent success imaging individual proteins and other small molecules with the AFM such as collogen. Smaller molecules that do not have a high affinity for common AFM substrates have been successfully imaged by employing selective affinity binding procedures.
Nano range force measurement
A variety of biological processes such as DNA replication, protein synthesis, drug interaction, and many others are largely governed by intermolecular forces.
These forces are in the nanonewton range. AFM has the ability to measure such forces. This force measurement makes it possible to quantify the molecular interaction in biological systems such as a variety of important ligand-receptor interactions. Using AFM force measurements, electrical surface charge can be imaged and quantified as the dynamics of many biological systems depends on the electrical properties of the sample surface. The binding forces, electrostatic forces and the micromechanical properties specifically, elasticity and viscosity of biological samples ranging from live cells and membranes to bone and cartilage can be analyzed.

Nanostructure etching technique

2011-08-26T11:50:00.000-07:00

Pattern creation
To create a desired pattern nanotechnology researchers use e-beam lithography and have conventionally traced a pattern within a layer called a "resist," which is then etched into the underlying substrate. But the resist is thin and fragile and hence intermediate "hard mask" is generally laid between the resist and the substrate.
The hard mask sticks to the substrate long enough for the desired features to be etched and then it id cleanly removed. But the extra layer often results in a dull, rough and costly.
A new technique
But researchers of Argonne's Center for Nanoscale Materials and Energy Systems Division have overcome this difficulty and developed a technique called sequential infiltration synthesis (SIS). This involves the controlled growth of inorganic materials within polymer films so that materials with unique properties and even with complex, 3-D geometries can be constructed.
The thin delicate resist film can be made robust by infiltrating it with inorganic material without an intermediate mask and creating very narrow features well over a micron deep using only a very thin, SIS-enhanced etch mask would be a breakthrough capability.
By combining sequential infiltration synthesis with block copolymers, molecules that can assemble themselves into a variety of tunable nanostructures, this technique can be extended to create even smaller features than are possible using e-beam lithography by designing a selective reaction between the inorganic precursor molecules and one of the components in the block copolymer.
This opens a wide range of possible applications for solar cells, electronics, filters, catalysts and all sorts of different devices that require nanostructures, but also the functionality of inorganic materials according to the re searchers.

Inorganic Molecular Machines

2011-08-25T04:17:00.000-07:00

Molecular devices
There are lots of molecular devices bearing resemblance to macroscopic machinery. For example chemical compounds behaving as bevel gears and propellers (Triptycyl and amide ring systems) have been reported. Similarly a molecular propeller can be formed when two or three bulky rings such as the aryl rings are connected to one central focal atom. Clockwise rotation of one ring induces a counterclockwise rotation of the opposite ring about the bond connecting it to the central atom.
‘Molecular Turnstiles’ which are rotating plates inside a macro cycle have been created, but their rotations were not controllable. But rotation of a molecular ring about a bond could be controlled by chemical stimuli in a device like a molecular brake.
A propeller-like rotation of a 9-triptycyl ring system connected to a 2, 2’-bipyridine unit could be controlled by the addition and subsequent removal of a metal to stop and release the free rotations along single bonds at will.
Molecular switch triggered by light
Another type of molecular switch is the ‘chiroptical molecular switch’ which is switchable between its two stable right and left handed isomeric forms stimulated by light. Depending on the frequency of light bombarded on it the trans conformations of specific compound can be interconnected.
A rotation can be achieved around a carbon-carbon double bond in a helical alkene when ultraviolet light or the change in temperature triggers a rotation involving four isomerization steps. A second generation motor along with 8 other motors from the same material is now operational. This redesigned motor has distinct upper and lower portions and at a higher speed and provides controlled motion at the molecular level. The light-driven motors when inside liquid crystal (LC) films can produce a color change by inducing a reorganization of mesogenic molecules.
The Catenane molecular motor
The catenanes are also molecular machines of special type of two interlocked ring-like components structures held together without any valence forces and both rings with similar recognition sites can have one of the rings rotating inside the other with the conformations stabilized by non covalent interactions.
When there are different recognition sites within the macro cycles, they can be controlled independently through their own specific stimuli. The stereo-electronic property of one recognition site within a macro cycle can be varied such that at one point it has more affinity to the sites on the other ring. Depending on the stimulus affinity it can be turned on or off, or even reversed. Catenanes also can be designed for chemical, photochemical or electrochemical control.
Molecular ball bearings
These molecular machines work a little like a pair of pliers. But opening one end of the structure's central X-shape does not widen the other end. Instead, the two prongs at that end twist around until they are 90° from their original position. This contortion is hinged on a pair of iron-based molecules that act as molecular ball bearings.
The mechanics of molecular machines is extraordinarily complex and depends on the dynamics of chemical bonds and nanoscale forces, as apposed to the relatively straight-forward engineering principles at work in large-scale mechanical devices.

Few uses of graphene

2011-08-25T04:10:00.000-07:00

Graphene as antibacterial Material

Scientists in the United Kingdom discovered graphene, in 2004. The commercial and industrial uses for graphene have been in solar cells, computer chips, and sensors and graphene oxide has superior antibacterial properties. Scientists have made sheets of paper from graphene oxide, and then grown bacteria on it. it can be mass-produced and easily processed to make freestanding and flexible paper with low-cost. This thinnest possible sheets of carbon with the built-in ability to fight disease-causing bacteria could have applications that range from anti-bacterial bandages to food packaging that keeps food fresher longer to shoes that ward off foot odor. This carbon nanomaterial may find important environmental and clinical applications.
Graphene for self-Powered sensors
Petroleum exploration is an expensive process involving drilling deep down in the earth and detecting the presence of oil or natural gas. A number of micro scale or nanoscale sensors are used into new and existing drill wells into the network of cracks that exist underneath the well to collect data on the presence of hydrocarbons. Nowadays to power these sensors convention power sources have to be used which becomes cumbersome. To overcome this problem researchers at Rensselaer Polytechnic Institute have shown that flow of water over surfaces coated with graphene which is a single-atom-thick sheet of carbon atoms which are arranged like a chain-link fence could generate small amounts of electricity to the tune of 0.2 W/sq.m, which could be sufficient to power them. A large numbers of micro scale or nanoscale sensors can be sent into new and existing drill wells to travel laterally through the earth, carried by pressurized water pumped into these wells.
This energy may be sufficient to power tiny sensors that are introduced into water or other fluids and pumped down into a potential oil well. As the injected water moves through naturally occurring cracks and crevices deep in the earth, the devices detect the presence of hydrocarbons and can help uncover hidden pockets of oil and natural gas.
As long as water is flowing over the graphene-coated devices, they should be able to provide a reliable source of power. This power is necessary for the sensors to relay collected data and information back to the surface.
The discovery is a potential solution for a key challenge to realizing these autonomous micro sensors, which will need to be self-powered. By covering the micro sensors with a graphene coating, the sensors can harvest energy as water flows over the coating. Oil companies would no longer be limited to vertical exploration, and the data collected from the sensors would arm these firms with more information for deciding the best locations to drill.
Principle
As water flows over the graphene, the friction force between the water flow and the layer of adsorbed chloride ions present in the water stick to the surface of graphene causing the ions to drift along the flow direction. The motion of these ions drags the free charges present in graphene along the flow direction and creates an internal current.
This means the graphene coating requires ions to be present in water to function properly. Therefore, oil exploration companies would need to add chemicals to the water that is injected into the well.
Uses
Energy harvested from water flowing over a film of graphene is an inexpensive solution. By using graphene the energy generation and performance was superior compared to even the nanotube. Future applications of this technology could be for self-powered micro robots or micro submarines and getting power from a graphene coating on the underside of a boat.

Appearance Potential Spectroscopy (APS)

2011-08-23T11:52:00.000-07:00

(photo courtesy; Texas A&M U)
Appearance Potential Spectroscopy (APS) was developed in the 1970’s by R.L.Park and J.E Houston. This is one of the various spectroscopic techniques used for measuring the binding energies of core level electrons. It is also called X-Ray Photoelectron Spectroscopy is one of the modern technique for measuring the binding energy. APS is so called because one determines the incident energy at which the relaxation products of a certain core hole appears. In this method soft X-Ray excites the core electron and makes it to emit radiation whose energy spectrum measured. The short penetration depths of electrons used makes APS highly surface sensitive.
In short the experiment is done in vacuum and thermally excited electrons are used as a source of excitation. The voltage to the sample is increased in steps. Following the excitation of a core level electron, the system will de-excite and appear as an emission of Auger electrons or Soft X-rays. Depending on what is monitored, the appropriate name is given to that technique.
Principle
This technique is based on the principle of measuring the threshold energy for the creation of inner shell excited atom. Threshold energy provides Information about the binding energies of electrons in the core levels of surface atoms.
In Appearance Potential Spectroscopy the intensity of auger or X-Ray emission as a function of the excitation threshold (Ep) can be Determined. This technique also gives information about the unoccupied states of a sample. In this respect it can be termed as an inverse Auger electron Spectroscopy in which the density of occupied states are mapped. APS can be used as a tool for the investigation of electronic structure of solid surfaces.
In APS the energy of the exciting particle is recorded and not the energy of the decay of the excited states. But the spectrum will be simple and can be easily interpreted. Compared to other techniques the instrumentation is very simple making it a valuable tool for surface analysis.
Appearance Potential Spectroscopy can be classified into Soft X-Ray Appearance Potential Spectroscopy (SXAPS), Auger Electron Appearance Potential Spectroscopy (AEAPS) and Disappearance Potential Spectroscopy (DAPS).
Soft X-Ray Appearance Potential Spectroscopy (SXAPS)
Soft X-ray Appearance Potential Spectroscopy SXAPS is a member of the Appearance Potential Spectroscopy with very simple experimental apparatus. A filament is mounted near the sample and emits electrons which are accelerated towards the sample. X-rays generated within the sample are detected via photoelectrons generated by the X-ray within the detector. Due to the long mean free path of X-rays in matter, it might be thought that SXAPS is not particularly surface sensitive, but as it is a threshold technique, the incident electrons will only travel a short distance before they are unable to excite the level of interest. As X-rays are very inefficiently generated, SXAPS suffers from poor signal.
Auger Electron Appearance Potential Spectroscopy (AEAPS)
AES is a popular technique for determining the composition of the top few layers of a surface. It cannot detect hydrogen or helium, but is sensitive to all other elements, being most sensitive to the low atomic number elements. AES must be carried out in UHV conditions. A popular method of looking at buried layers with AES is to use the technique in combination with sputter cleaning.
DAPS -Disappearance Potential Spectroscopy
DAPS is used to detect ionization thresholds of core levels in atoms. This is done by bombarding the surface with electrons and modulating the energy of the primary beam. The electrons emitted from a surface can be detected with RFA and measuring the current to ground from one of the hemispherical grids. If the primary beam voltage is such that a core peak is on the edge of being excited, then changes in the current emitted from the surface can be detected using standard modulation techniques.
Applications
AEAPS is useful for studying Low Z materials and the signal is recorded in the second differential mode. Low temperature AEAPS can be use to conduct temperature variation studies.
APS technique is non-dispersive in nature. As signal is extracted from the background using potential modulation technique, its strength is proportional to the Unoccupied Density of States at the Fermi Level. In an APS spectrum, the peaks provide a means of elemental identification. The threshold can be used to measure the Binding Energy and the chemical shift correlates to changes in the chemical bonding.

Modeling of carbon onions

2011-08-20T04:28:00.000-07:00

Carbon onions
Since the discovery of fullerene molecules and subsequent carbon nanotubes, carbon nanomaterials with curved surface have gained great interests because of their novel mechanical and electronic properties. Carbon onions, which consist of concentric spherical graphitic sheets, are one important member of the fullerene family.
Consisting of concentric fullerene-like structures, carbon onions can be formed in a variety of harsh environments such as high energy electron irradiation of a carbon precursor, thermal annealing of diamond nanoparticles, carbon ion implantation, and arc discharge from a carbon target in water.
Onions like structures have also been observed in soot and interstellar dust. In each case, the formation of onions involves high-temperature heating of carbon precursors, but the nucleation mechanism and range of possible microstructures are poorly understood.
The formation mechanism of carbon onions has remained a mystery, several conceptual models have been proposed for how the onions nucleate and form a three-dimensional structure.
Shrinking hot giant model
Simulations have proven highly successful in understanding the formation mechanism of fullerenes, which nucleate by the shrinking hot giant model, whereby a cluster of atoms form large, closed, caged structures by the aggregation of atoms before shedding chains of sp-bonded atoms to form smaller, energetically favorable, fullerene structures. Multi walled carbon onions can be formed from a variety of precursors including amorphous carbon and nano diamond, but the key factors which control the carbon onion microstructure are temperature and annealing time.
Continuum model
Todt and others of Vienna University of Technology, Austria have made a Continuum modeling of Van der Waals interactions between carbon onion layers by deriving relations analytically considering the doubly-curved geometry of carbon onion layers. They report that the Van der Waals induced pressures on opposing faces of two adjacent onion layers are not equal and depend on radii of both layers. The curvature effects have no significant influence on the equilibrium interlayer distances, but they significantly change the results for the radial displacements and, consequently, for the membrane forces in the layers. They did Monte Carlo simulations of C60 in C180 and C60 in C240 and concluded that the derived van der Waals model represents the radial displacements and equilibrium interlayer distances better than the simplified models.

Carbon nanofibers and application

2011-08-19T11:56:00.000-07:00

Carbon nanofibers hold promise for technologies ranging from medical imaging devices to precise scientific measurement tools, but the time and expense associated with uniformly creating nanofibers of the correct size has been an obstacle. Vapor-grown carbon nanofibers are within the class of multi-walled carbon nanotubes (MWCNTs), and are produced by the floating catalyst method. Carbon nanofibers (CNFs) are discontinuous, highly graphitic, highly compatible with most polymer processing techniques, and they can be dispersed in an isotropic or anisotropic mode.
Researchers have shown that nickel nanoparticles coated with a ligand shell can be used to grow carbon nanofibers that are uniform in diameter. Using nanoparticles to grow nanofibers is useful, because the fibers tend to have the same diameter as the nanoparticles they are growing from and allow to define where the nanofibers grow and how they are arranged by arranged in that pattern before growing the fibers.
Manufacturing technologies
Carbon nanofibres can be manufactured by the following CVD techniques:
1. Growing on metal catalysts seeded on a substrate.
2. Floating catalyst technique, and
3. Carbon Nanofibres growing on a substrate: The process is non continuous and needs separation from the substrate.
Floating catalyst technique
In the floating catalyst technique, metal catalysts are introduced in a continuous way by the upper end of a reaction chamber kept at a temperature of 1050 - 1100ºC. The catalysts descend through the furnace and the hydrocarbons used are decomposed on the surface of the catalysts growing and thickening the nanofibres. Catalytic particles used are elements of group VIII of the periodic chart like iron, nickel or cobalt, or alloys of them. The carbon sources are hydrocarbons like benzene, n-hexane, methane and acetylene.
Continuous fabrication
Researchers at the University of Illinois have developed continuous fabrication process of complex, three-dimensional nanoscale structures to grow individual nanowires of unlimited length. To draw longer nanowires, the researchers developed a precision spinning process that simultaneously draws and winds a nanofiber on a spool that is of millimeters in diameter.
Based on the rapid evaporation of solvent from simple "inks," another process has been used to fabricate freestanding nanofibers, stacked arrays of nanofibers and continuously wound spools of nanowires.
Making nanofiber anode
The nanofibers can be created by dispersing nickel nanoparticles consistently on a fused silicon substrate covered with a fine chromium grid which acts as an electrode. The set up is then kept in a chamber at 700°C, and later filled with ammonia and acetylene gas. The chromium grid acts as a negatively charged electrode, and the upper part of the chamber comprises a positively charged electrode.
For preparing porous carbon nanofibers used as anode materials in lithium-ion batteries, the procedure involves electro spinning of polyacrylonitrile (PAN) solutions in N, N-dimethylformamide (DMF) which contains silica nanoparticles. The electro spun composite nanofibers are subsequently carbonized at 700° C. Finally, the silica nanoparticles are removed using hydrofluoric acid, thereby resulting in nanoporous structures.
Applications
The commercial nanofibers are 10 – 80 nm thick Multi-Wall NanoTube (MWNT) carbon structures with less than 1% (mass) of Ni. These have excellent mechanical properties, high electrical conductivity, and high thermal conductivity which can be imparted to a wide range of matrices including thermoplastics, thermo sets, elastomers, ceramics and metals. Carbon nanofibers also have a unique surface state, which facilitates functionalization and other surface modification techniques to tailor/engineer the nanofiber to the host polymer or application. Carbon nanofibers are available in a free-flowing powder form (typically 99% mass is in a fibrous form).
Potential applications include electronic interconnects, biocompatible scaffolds and nanofluidic networks. The industrial applications of this material include: polymer and elastomer fillers, lightweight bulletproof uniforms, commercial hydrogen storage systems, radio wave-absorbing composites, lithium battery electrodes, construction composites, oil additives, and gas-distribution layers for fuel cells, filters and absorbents.
The carbon nanofibers in thermoplastic materials have fire retardant properties. Composites loaded with carbon nanofibers and exposed to a flame exhibit delayed and lower peak heat release rates, lower smoke emissions, and no dripping or pooling of molten polymer.
The nanofiber coatings are used for applications in water repellent coatings, solar cells, biomedical research tools, and many others.
The carbon nanofiber-filled coatings devised by researchers from the National Institute of Standards and Technology (NIST) and Texas A&M University outperformed conventional flame retardants used in the polyurethane foam of upholstered furniture and mattresses by at least 160 percent and perhaps by as much as 1,130 percent.
Among many possibilities, nanofiber applications are as follows:
• Soft protective vests stronger than Kevlar
• Bandages that can contract to put pressure on
• Artificial muscles powered by electricity - much lighter than current hydraulics
• making easier to incorporation of electronic sensors and actuators into clothing
Sector wise nanofiber applications are listed below:
Automotive sector
Thermoplastic reinforcement (glass fibre replacement), under hood components subjected to mechanical efforts at high temperatures (thermal stability). Fuel system, Paintable parts, Exterior panels, Embedded Electronics.
Electronic sector
Packaging, materials for ESD, sensitive items, Hard Disk Drive manufacturing, EMI shielding, Semiconductor, manufacturing, Clean room Equipment.
Energy sector
Bipolar and end plates, Electrode catalyst, support in PEM fuel cells, Hydrogen Storage
Aerospace sector
High Performance, Conductive Adhesives, Microelectronics, Sensors, Enhanced Thermal Management, Broadband EMI Shielding, Nanocomposite, Rocket Ablative Materials, Conductive Coatings and
Paints, Light Weight Antennas and Ground Planes.
Chemistry sector
Catalyst Support.
Conductive plastic resins filled with graphite fibril nanofibers can be used in molded clean room tools such as wafer trays, bar code scanners, and tweezers. The resins produce a non sloughing, glossy surface with low out gassing levels.
In electronics, polycarbonate and polyetherimide (GE’s Ultem) components of computer hard drives have been reinforced with nanotubes to render them conductive and very smooth
Other applications are:
ESD Control of Isolated Metallic Standoffs
Electrically Bonded Structural Joints for
Inter Panel Power/Signal Return Currents
Electrically Conductive NanoAdhesive Advantages
Improved ESD of metallic components w/o added adhesive bead
Elimination of inter panel jumper cabling
Nanofiber coatings
North Carolina State University researchers have identified a novel technique to grow straight carbon nanofibers atop a transparent substrate. The technique uses a grid made of charged chromium and with the help of ions ensures that the developed nanofibers do not get curled because curling of the nanofibers will hinder its usage.
In particular, genetic material can be coated on the nanofibers and introduced into the cell’s nucleus, for instance, to enhance the research of gene therapy. Scientists can pass light through the transparent substrate, which results in better contrast and better visibility of the process taking place.
Hydrogen storage
Carbon nanofibers used for hydrogen storage consist of coil like fibers made up of very small graphite sheets that are stacked in specific configurations and separated by distances of 0.335 – 0.342 nm.
Carbon nanofibers are grown from the decomposition of carbon-containing gases such as hydrocarbons over metal or alloy surfaces which act as catalysts to the sheets’ formation. During the reaction, the carbon-containing gas molecules are adsorbed to certain faces of the catalyst’s surface and are subsequently decomposed. Following this, the carbon atoms diffuse through the catalyst particle and precipitate at one or more other surfaces and form successive sheets that stack on one another to form the carbon nanofibers.
When carbon nanofibers are placed in a vessel and exposed to hydrogen under pressures of 120-130 atm at room temperature, the hydrogen slips between the graphite sheets of the carbon nanofibers and adsorbs to surface of the carbon layers. To prepare the carbon nanofibers for hydrogen adsorption, they are carefully pretreated to remove any metal impurities and chemisorbed gases that may be present.
Carbon Nanofibers scaffold for heart
Engineers at Brown University and the India Institute of Technology in India have created a carbon nanofiber based scaffold that promotes regeneration of heart tissue. The researchers developed a mesh by stitching the carbon nanofibers together using a PLA polymer. The resulting mesh is also elastic, durable and enables the product to expand and contract with the heart tissue.

Synthesis of pure carbon nanotubes

2011-08-18T01:38:00.000-07:00

Carbon nanotubes are currently produced in batches and are difficult to make in large quantities. But only a handful of nanotubes made in batch possess the desired characteristics. For carbon nanotubes to be commercialized and to replace silicon wafers in electronics, they should be easy to make in the purest form possible with high precision and yield.
Berkeley Lab scientists developed a hoop-shaped chain of benzene molecules called cycloparaphenylene to improve the way carbon nanotubes are produced, and the newly synthesized nanohoop happens to be the shortest segment of a carbon nanotube and this could be used to grow much longer carbon nanotubes in a controlled way, with each nanotube identical to the next.
Thus a way to has been opened to make a single type of carbon nanotube on demand by rational synthesis. To synthesize cycloparaphenylene the scientists developed a relatively simple, low-temperature way to bend a string of benzene rings which normally resist bending into a hoop.
Carbon nanotubes are hollow wires of pure carbon which is semi conducting or metallic depending on how they’re structured to help in constructing faster and smaller computers or tiny sensors powerful enough to detect a single molecule.
The family of Cycloparaphenylene compounds forms the smallest carbon hoop structure with a set diameter and set orientation of benzene molecules, which are the two variables that determine a nanotube’s electronic properties. Because of this, cycloparaphenylene molecules could be used as seeds or templates to grow large batches of carbon nanotubes with just the right specifications.
The researchers have created a batch of carbon nanotubes that is 99 percent pure and made cycloparaphenylenes, called carbon nanohoops because they are the fundamental circular building blocks of “armchair” conformation of carbon nanotubes.
Cycloparaphenylenes are fundamental repeating units of armchair carbon nanotubes. Synthetic cycloparaphenylenes could make it possible to assemble pure armchair nanotubes under low-temperature conditions.
The diameter and structural conformation of carbon nanotubes cannot be controlled by available assembly techniques, but conceivably be controlled by using carbon nanohoops as seeds for nanotube growth.

Carbon nanohoops

2011-08-17T11:33:00.000-07:00

The shortest carbon nanotube having one molecule high carbon is called “nanohoop”. It is a tiny ring of carbon, called cycloparaphenylene and will have impact on the development of faster electronic devices, more powerful sensors, and other advanced technologies.
Nanohoops
Single-walled carbon nanotubes (SWNT) can be thought of as built from component macro cycles, often called nanohoops. For example, cycloparaphenylenes can be the thought of as the precursor (at least in principle) of armchair SWNTs. To create chiral SWNTs, cycloparaphenylene-naphthalene and other acene substituted macro cycles can serve as appropriate precursors.
Nanohoops are macro cycles formed of aromatic rings linked in a 1, 4’ fashion. The nanohoops contain 3-24 repeat units. The strain energy of the nanohoops exponentially decreases with the number of building blocks n, and this strain strongly correlates with the bend angle at the ipso carbons.
Cycloparaphenylene synthesis offers a more targeted approach. This family of benzene-derived compounds forms the smallest possible carbon hoop structure, one molecule high. It also has a fixed diameter and orientation, the two variables that determine a nanotube’s electronic properties. Because of this, cycloparaphenylene molecules could possibly be used as seeds or templates to grow large batches of carbon nanotubes with precisely defined structures.
Carbon nanohoops have smaller optical absorption gaps and this counterintuitive trend, opposite to that expected from ordinary quantum confinement, reflects a large increase in electron-hole interaction strength with decreasing hoop diameter.
Silver nanohoops
Silver nanohoops are a metamaterial and exhibit an antisymmetric resonance that presents a highly negative real part of the permeability at visible wavelengths. The strength of this magnetic resonance is easily tunable through the inner radius of the nanohoops.
Synthesis
The hoop-shaped chain of benzene molecules had eluded synthesis, despite numerous efforts, since it was theorized more than 70 years ago. Their strained and distorted aromatic systems and radially oriented p orbitals have intrigued synthesis. The first synthesis and characterization ofcycloparaphenylene was demonstrated utilizing a novel aromatization reaction.
The heart of the synthetic challenge lies in overcoming the strain energy required to bend a string of benzene rings which normally resist bending into a hoop. The strain is considerable and increases with decreasing ring size: 5, 28, and 47 kcal/mol for hoops with 18, 12, and 9 benzene units, respectively.
Researchers used a strategy that involved the build- up of strain sequentially during the synthesis, using carefully selected small molecule precursors in combination with a cyclohexadiene molecule designed to provide the curvature and rigidity necessary for the ring to form. The strategy was successful and rings with 5, 8, and 14 benzenes were obtained in good yield (>35%).
Carbon nanotubes
Carbon nanotubes are hollow wires of pure carbon and can be semi conducting or metallic depending on their structure. Carbon nanotubes also feature extremely high electrical conductivity, very small diameters (much less than 100 nanometers), large aspect ratios (greater than 1000), and a tip-surface area near the theoretical limit (the smaller the tip-surface area, the more concentrated the electric field, and the greater the field enhancement factor). These features make carbon nanotubes ideal candidates for electron field emitters, white light sources, lithium secondary batteries, hydrogen storage cells, transistors, smaller computers, or tiny powerful sensors even to detect a single molecule and cathode ray tubes (CRTs).
In spite of this feature they have not yet penetrated much into the electronics or other sectors, because they are difficult to make with defined structures in large quantities. At present, they are produced in batches in laboratories, with only few nanotubes in each batch possessing the desired characteristics. This approach is inefficient for commercial applications. Hence scientists are working to improve and systematize the way carbon nanotubes are produced. In order to use the carbon nanotubes more widely and more effectively, it is necessary to implement a controlled growth of the carbon nanotubes with desired structural parameters.

Polymer nano composites

2011-08-13T11:30:00.000-07:00

Nanocomposite
A nanocomposite is as a multiphase solid material where one of the phases has any one or all dimensions less than 100 nm, or structures having nanoscale repeat distances between the different phases that make up the material. This definition is more usually taken to mean the solid combination of a bulk matrix and nano-dimensional phase(s) differing in properties due to dissimilarities in structure and chemistry. By adding nanoparticles to a polymer matrix its performance can be enhanced greatly due to the nature and properties of the nanoscale filler. Polymer-based nanocomposites are becoming increasingly attractive in the field of industry. In order to achieve tailor-made properties, a large number of basic polymers are being applied together with minerals such as silicates, clays, carbon nanotubes, or metallic particles either as individual materials or as closely defined agglomerates.
Nano filler
Nano filler materials can be used to improve plastic composite materials. These materials require only less than 5 wt% of nano-filler as against conventional standard fillers to yield marked improvements in mechanical, thermal, electrical and other properties such as gas impermeability, dimensional stability and flame retardance. Furthermore, all of these benefits are available without sacrifices in composite density or light transmission of matrix resins. Nano fillers provide more than three times interfacial area per particle than conventional mineral fillers.
Nanoclays and nanotubes are two types of nano-fillers used in commercial products, such as carbon nanotubes and aluminum silicate nanotubes. But both types of nano-filler materials require surface modification prior to use.
Structure of clay material
Nanoclays for plastic composite refer to a category of clay minerals with a specialized structure, characterized by plate morphology such as modified montmorillonite clay with a 2-to-1 layered smectite clay mineral. Each layer has 2 tetrahedral sheets containing an octahedral sheet between them. Individual platelet thicknesses are just one nanometer, but surface dimensions are generally 300 to more than 600 nanometers, resulting in a very high aspect ratio. Hundreds or thousands of these layers are stacked together with van der Waals forces to form clay particles to have a thickness of only 1 nm.
Characteristics of clay material
For commercial applications, nanoclays are modified in a two-step process and incorporated into the resin matrix either during polymerization or by melt compounding. In the first step, the hydrophilic surface property of natural existing montmorillonite is changed to hydrophobic for compatibility with organophilic polymers that are generally used in composites. The most popular surface treatment method exchanges organic ammonium cations with existing inorganic cations on the clay’s surface and are known as organoclays.
Nanoclays normally exist as agglomerated bundles, consisting of thousands of platelets held together by van der Waals force. In the second step, individual clay platelets are separated from each other called exfoliation, but complete exfoliation is not always good. To get gas barrier function and promote good clarity of packaging materials, the platelets are fully exfoliated by combining surface compatibilizing agents and process shear in the plastic matrix. Complete exfoliation in polyolefin material decreases particle reinforcement, which may be a problem for automotive application. Commercially nanoclays are sold with more than 95% of exfoliation and even distribution within polyamide plastics.
Fabrication methods
Various fabrication methods such as in situ polymerization, Solution-induced intercalation and the melt process are used.
In situ polymerization
In this process polymer precursors are inserted between the clay layers to make them expand. The expanded clay layers are then dispersed into the matrix by polymerization to produce well-exfoliated nanocomposites applicable to a wide range of polymer systems, and are particularly useful for thermosetting polymers.
Solution-induced intercalation
This method can be used for commercial production. It uses solvent to swell and disperse clays into a polymer solution and mainly uses for water-soluble polymers because of the low cost of water as a solvent as well as its low health and safety risks. However, this method is not applicable to most engineering (i.e., non-water soluble) polymers because of high solvent cost, and health and safety concerns.
The melt process
This method can use traditional techniques such as extrusion and injection molding to produce nanocomposites and is easily adapted to commercial production. During the melt process, clays and polymers are intercalated with each other. The efficiency of intercalation is lower than in situ polymerization and often produces a partially exfoliated structure.
Applications
A combination of nylon and nanoclay is used for barrier layers in multilayer polyethylene terephthalate (PET) bottles and films for food packaging. Nanoclays in composite materials act as a barrier and arrest gas molecules permeation through the matrix resin. Also, because nanoclays do not degrade in the matrix, the gas barrier property is maintained over time. These clay nanocomposites are used for oxygen (O2) and carbon dioxide (CO2) sensitive products. Major applications of plastic nanoclay composite materials are in automotive parts, such as automotive body panels and under-hood components, and packaging. Nanocomposites provide high stiffness and impact resistance that are used for electrical parts, power-tool housing, appliance components, pallets, and dunnage.
An example of commercial nanocomposite materials on the market is timing belt cover and food packaging, based on nylon 6 with nanoclays marketed by Toyota. Many other companies produce plastic nanocomposite materials for packaging and automotive parts. Nanoclay can also be applied to reinforce fabrics by adding 1 wt% to improve mechanical properties of polypropylene fabrics. Nanoclay can potentially also be used in thermoplastic/natural fiber composites to improve their mechanical properties.

Dendrimers for cancer therapy

2011-08-13T00:03:00.001-07:00

Dendrimers
Dendrimers were first discovered in the early 1980’s by Donald Tomalia and co-workers. Dendrimers are chemically synthesized nanoparticles in which a branching monomer is polymerized to give tree-like structures organized around a central molecule, resulting in an atomically defined, more or less spherical nanostructure. The structure of these materials has a great impact on their physical and chemical properties. As a result of their unique behavior dendrimers are suitable for a wide range of biomedical and industrial applications.
Applications
Dendrimer can easily be modified with molecules because of the presence of many functional chemical groups on the surface that provide added functionality to the dendrimer, such as molecules that target particular cells, and chemotherapy drugs as cargoes. Dendrimers can be used in molecular electronics for the storage of information or for nanoelectronics, as gene delivery agents or nanoscale reactors for catalysis, in addition to building blocks for nanotechnology. The novel dendrimers and other polymeric materials can also be used in a variety of separation and molecular recognition processes and as functional components of miniaturized "labs-on-a-chip."
Structure
According to Berkely Lab report, in a dendrimer, the branches are interlinked polymerized chains of molecules, each of which generates new chains, all of which converge to a single focal point or core. The surface of a dendrimer globe bristles with numerous chain-ends. During synthesis, these chain-ends can be designed to perform specific chemical functions. For example, they may be electrically charged so that the entire dendrimer functions as a polyelectrolyte. Other features, including the external size and internal architecture of a dendrimer can also be controlled during synthesis. This makes possible the creation of interior cavities or channels with properties different from those on the exterior and opens the door to dendrimers serving as vessels or hosts for guest molecules. In this capacity, dendrimers could serve as targeted drug.
Synthesis
The first synthesized dendrimers were polyamidoamines (PAMAMs). They are also known as starburst dendrimers. Dendrimers are generally prepared using either a divergent or convergent methods.
Divergent method
In the divergent methods, dendrimer grows outwards from a multifunctional core molecule. The core molecule reacts with monomer molecules containing one reactive and two dormant groups giving the first generation dendrimer. Then the new periphery of the molecule is activated for reactions with more monomers. This process is repeated for several generations and a dendrimer is built layer after layer. The divergent approach is successful for the production of large quantities of dendrimers.
Demerit
But problems occur from side reactions and incomplete reactions of the end groups that lead to structure defects. To prevent side reactions and to force reactions to completion large excess of reagents is required. It causes some difficulties in the purification of the final product.
Convergent method
In the convergent approach, the dendrimer is constructed stepwise, starting from the end groups and progressing inwards. When the growing branched polymeric arms, known as dendrons, are large enough, they are attached to a multifunctional core molecule. It is relatively easy to purify the desired product and the occurrence of defects in the final structure can be minimized. It becomes possible to introduce subtle engineering into the dendritic structure by precise placement of functional groups at the periphery of the macromolecule.
Demerit
Convergent growth method has several advantages. The convergent approach does not allow the growth of high generations because steric problems occur in the reactions of the dendrons and the core molecule.
Properties
In solution, linear chains exist as flexible coils; in contrast, dendrimers form a tightly packed ball. This has a great impact on their rheological properties. Dendrimer solutions have significantly lower viscosity than linear polymers. When the molecular mass of dendrimers increases, their intrinsic viscosity goes through a maximum at the fourth generation and then begins to decline. Such behavior is unlike that of linear polymers. For classical polymers the intrinsic viscosity increases continuously with molecular mass.
Anti-cancer drugs
Dendrimer can deliver cancer fighting drug to head and neck tumors. Head and neck cancer has been the more difficult malignancies to treat and after successful treatment patients suffer severely from the available therapies. Researchers at the University of Michigan have reported using a model study that dendrimers targeted to tumors and carrying anti-cancer drugs show great promise as potential therapy for head and neck cancer. Dendrimer decorated with folic acid on its surface delivers the drug methotrexate to head and neck tumors. The tumor-targeted nanoparticle delivers high doses of anticancer agents directly to head and neck tumors.

Carbon onions - synthesis and properties

2011-08-08T12:03:00.000-07:00

Low-temperature synthesis
Low-temperature synthesis of carbon onions by chemical vapor deposition using a nickel catalyst supported on aluminum
A mass of carbon onions have been successfully synthesized via catalytic decomposition of methane over an Ni/Al catalyst at a low-temperature (600 °C). The carbon onions as-obtained have diameters ranging from 5 to 50 nm and consist of several concentric carbon layers surrounding a hollow core.
A practical method for the production of hollow carbon onion nanoparticles
Researchers at Tianjin University have developed a method for obtaining pure carbon onion nanoparticles in large quantities. They use nitric acid to dissolve the nickel from the carbon-coated nickel nanoparticles. In this method, the decomposition of methane in the presence of Ni/Al catalyst particles produces carbon nano-onions as the primary product. And the nanoparticles with nickel nanoparticle encapsulated are very easily purified to be hollow onions by the subsequent nitric acid treatment. The method requires a relatively low energy input with the correct choice of catalyst precursor and purification time, thus making it industrially attractive.
Carbon implantation
To make carbon onion with carbon implantation, 120 KeV carbon ions implant into crystalline copper substrate at 700º to 1000ºC. During the process, 10-5 Pa of vacuum is maintained. Carbon onions are formed on the surface of substrate.
Formation of carbon onions with Pd clusters in a high-resolution electron microscope
Carbon onions have been produced in a transmission electron microscope by electron irradiation of amorphous carbon in the presence of Pd clusters and form intercalated onions. High-resolution electron microscopy revealed structural changes of the onion surface, and atom clouds were observed at the pentagonal vertices. In some onions, Pd atoms were intercalated between the graphite onion sheets, and a structural model for the intercalation has been proposed.
Anode Materials for Rechargeable Lithium-Ion Batteries
Researchers of China prepared Carbon nano-onions (CNOs) at 600 °C by a simple reaction between copper dichloride hydrate (CuCl2•2H2O) and calcium carbide (CaC2). The morphology and structure revealed that large quantities of CNOs consisting of quasi-spherically concentric graphitic shells with high purity and uniform size distribution (about 30 nm) were obtained. The crystal water in CuCl2•2H2O plays an important role in the formation of CNOs. The CNOs as-obtained exhibit high capacity and excellent cycling performance as anode materials for lithium-ion batteries, which can deliver a reversible capacity of 391 mAh g–1 up to 60 cycles.
Carbon onions give diamond
Researchers of Germany have reported that spherical particles of carbon consisting of concentric graphite-like shells ('carbon onions') can be formed by electron irradiation of graphitic carbon materials. When such particles are heated to nearly 700 °C and irradiated with electrons, their cores can be transformed to diamond. Under these conditions the spacing between layers in the carbon onions decreases from 0.31 in the outer shells to about 0.22 nm in the core, indicating considerable compression towards the particle centres which allows diamond to nucleate—in effect the carbon onions act as nanoscopic pressure cells for diamond formation.
Researchers of University of Edinburgh in the UK explain the reason further that the radiation bombardment knocks entire atoms out of the structure of nanotubes, causing the resulting defects to ricochet through the structure. This makes the structure bend and buckle, eventually forming into carbon spheres.
In fact, under intense radiation bombardment, this process turns multiwall nanotubes into carbon onions, ie concentric spheres. As more atoms are knocked out of the structure, the spheres shrink, placing enormous streeses on the layers beneath. It is this stress and resulting pressures that eventually causes diamond to nucleate and form at the centre of the onion.
Carbon-onions for ultra capacitors
Ultra capacitors or super capacitors are electrochemical systems that store energy within their double-layered structure consisting of opposite charged materials.. Electrodes made from activated or porous carbon are used in the production of the highest rated super capacitors. Although this provides a high storage capacity, it slows down the rate at which charging and discharging occurs.
The integration of carbon onions has opened new horizons in the use of micro-scale energy storage for applications for which conventional electrolytic capacitors are not sufficient. The use of onion-like carbons (OLC) in the development of micro-super capacitors now seems to be a promising venture.
A team of researchers made a capacitor using onion-like shells of graphene for electrodes to get enhanced energy and power densities.
Although their surface area is rather low compared to the surface of the activated carbons, it has qualitative value since it is fully accessible to the electric charges. The team began with creating an exposed electrode out of OLC. The OLC (at 6-7 nm diameters) could adhere onto the electrode without any binding agent or polymer separator making the process easier.
The rate of charge and discharge and power density was very high compared to the activated carbon capacitor and thin film lithium battery.
Applications
Applications include portable electronics, ultra capacitor technology biomedical implants, micro-sensors, etc. Their various properties enable them to serve as nanocapsules for drug delivery. In the nanocapsule drug delivery systems the external graphite layers providing protection to substances contained within and can serving as a template for the attachment of desirable functional groups. It can be used in other applications such as components of magnetic recording systems, magnetic fluids, electromagnetic shielding materials, reinforcement of composite materials, magnetic storage media, wear-resistant materials etc. They are also a potential solid lubricant similar to Tungstenite (WS2) nanoparticles having an onion-like structure. Carbon onions can even serve as
Bucky diamond (onion) coexists with nanodiamond
The transformation of nanodiamonds into carbon onions, and vice versa, has lead to the introduction of a new intermediate phase of carbon, coined “bucky diamond,” with a diamond core encased in an onion-like shell. Using a model based on the atomic heat of formation to describe the phase stability of carbon nanoparticles Australian researchers showed that bucky diamond occupies a coexistence region, spanning the calculated upper limit of fullerene stability and the lower limit of nanodiamond stability.
Electromagnetic Wave-Absorbing Coatings
A team of investigators from Belarus, Belgium, Russia and the United States have developed coatings that can efficiently absorb wide-band electromagnetic waves. This could be used as a countermeasure against terrorists who try to use electromagnetic radiation to lock-on to airplanes with surface-to-air missiles or to disrupt their avionics. Electromagnetic wave-absorbing technology can be used to reduce radar signatures. The basic absorbing component is onion-like carbon (OLC), which is produced by the transformation of nanodiamonds. These carbon nanostructures have specific properties that make them ideal materials for electromagnetic wave absorption.
The OLC is embedded in a polymer layer, which would then be deposited on the surface of the device to be protected. Nanodiamond aggregates of defined size and surface group composition are purified and OLC and OLC-based nanocomposites are incorporated into polymer matrixes and films. Nanodiamond fractions have now been developed and a series of OLC-polymer composites has been fabricated. Films with nanodiamonds have also been fabricated. Test results confirmed that OLC is an efficient shielding material for
Lubricating nanoparticle
The carbon nano-onion can be considered as a new kind of interesting lubricating nanoparticle. Used as lubricant additives, carbon nano-onions lead to a strong reduction of both friction and wear, even at low temperature.
It is found that lubricious iron oxide nanoparticles are generated in the core of the steel contact through mechanisms that are not yet known. The molecular dynamics simulation indicates that the lubrication mechanism of the onions is based on a coupled process of rolling and sliding inside the contact area. most of carbon onions seem to remain intact under friction processes and do not generate graphitic planes, which is in contrast to the previously determined behavior of MoS2 fullerenes that are mainly exfoliated inside the contact area and liberate lubricating lamellar sheets of h-MoS2.
Solid lubricant layer
Japanese researchers formed carbon onion layer compounded with gold by dispersing carbon onions on a silicon wafer coated with gold. The carbon onion layer compounded with gold has kept lower-friction coefficient for a longer time than gold layer in a certain range of gold film thicknesses and normal forces. in addition, carbon onion layer on a self-assembled monolayer exhibited the low-friction property under a wide range of normal forces.