Iron oxide nanowhiskers
Iron oxide nanowhiskers with dimensions have been synthesized by selectively heating an iron oleate complex. Such nanostructures resulted from the difference in the ligand coordination microenvironments of the Fe(III) oleate complex. A ligand-directed growth mechanism is proposed to rationalize the growth process of shape-controlled nanostructures for the formation of the nanowhiskers.
C60 nanowhiskers
C60 nanowhiskers can be formed by the liquid-liquid interfacial precipitation technique which is a low-cost means of fabricating nano-structured fibres. C60 nanowhiskers can be used as active or passive elements in a number of possible applications in electronic devices with switching or sensing capabilities, low-cost, robust millimeter-wave power detectors.
Nanotube whiskers
Researchers at Massachusetts Institute of Technology in Cambridge have developed a chemical process in which carbon fibers, heated to 750° C, sprout nanotube whiskers. They then wove those stubbly fibers into a fabric, which they injected with epoxy. The nanotubes tied the layers together and created a Velcro-like effect.
Silicon nanowhiskers
When a wafer of silicon is slowly heated under high vacuum conditions, the structure of the silicon rearranges itself to form tiny little pillars of silicon of around 10nm high and self-assemble all over the surface so that one square cm might have four billion nanowhiskers. Since the tips of the nanowhiskers are very sharp, it only takes a small field to induce the whiskers of very high density. This makes them suitable for using in low field electron emitters of small and light size suitable for use in portable devices like computer displays and widescreen televisions.
Making silicon nanowhiskers
Nanowhiskers are fabricated using GNS process as follows.The Si(100) substrate (either p-type or n-type) is cleaned to remove any surface dust or dirt but the native oxide layer is not removed, so this stage is very simple and quick. In some cases ions are implanted into the surface and the substrate is inserted into a high vacuum chamber and heated using a raster scanned electron beam that scans over the substrate at high speed, heating it in a homogeneous way. The sample is slowly raised to a peak temperature of 900- 1100C and held for a few seconds and then cooled again. The substrate is removed from the vacuum at room temperature to get nanowhiskers covered over it.
Nanowhiskers formation
Nanowhisker formation occurs in a two-stage process. Firstly, decomposition of the native oxide layer occurs. Voids form in the oxide film exposing clear silicon underneath. Silicon from the voids reacts with the oxide layer and the voids grow laterally until they coalesce. This causes a roughening of the surface and an uneven surface potential energy. After complete oxide adsorption Si species begin to migrate across the surface to kinetically favoured sites or nucleating islands. Island number and size grows as the annealing continues resulting in the growth of crystalline pillars.
Sic whisker powder
Sic whisker powder are available at a purity of 99%, diameter 1-2.5micron, L/D>=20 and in cubic crystal figure.Sic whisker powder has the good chemistry stability, low heated expansion, and high efficiency of heat conductivity, electrical resistance compared with metal being in the opposite direction and very hard. Sic resists heat, grinding and crushing, especially in resisting hot shock wave, corrosion and radiation. It is used for the fuselage cover of shuttle space craft, ceramics cutting tools, measurement tools and mould, for functional ceramics, bullet-proof ceramics and piezoelectric ceramics, ceramic bearings, far-infrared ray generator, spray nozzles, radiant tubes and combustors on machine.
ZnO nanowhiskers
Researchers report that vvertically aligned ZnO nanowhiskers can be grown on Si substrates spin-coated with ZnO nanoparticles by metal organic chemical vapor deposition (MOCVD) using Me2Zn•tmeda and a mixture of O2 and Ar gases. The ZnO nanowhiskers grown are single crystals with a growth rate of 3 μm h−1.
Blanket-like assembled ZnO nanowhiskers were fabricated using a freestanding ZnO nanoparticle layer by an aqueous solution deposition. Thermal treatment of the zinc acetate dihydrate layer resulted in the formation and delamination of the ZnO nanoparticle layer on the glass substrate. The growth habits of ZnO crystals resulted in the growth of ZnO nanowhiskers preferentially orientated along the direction of the c-axis on the whole surface of the freestanding ZnO nanoparticle layer by heterogeneorous nucleation and growth. The hierarchical-structured blanket-like ZnO nanowhisker assemblies can be utilized for dye-sensitive solar cells and gas sensors because of their high surface-to-volume ratio.
Single crystalline GaAs whiskers
Researchers have carried out under carefully selected conditions the hetero-epitaxial growth of branched III-V nanowhiskers on epitaxially grown group IV nanowires. They have also demonstrated this for single crystalline GaAs whiskers, a direct band gap semiconductor with high electron mobility predestined for nanophotonics, grown on Si nanowires forming hierarchical star-like structures with a six-fold symmetry. The hetero-epitaxial growth and the good crystallinity of the Si nanowires and wurtzite-type GaAs whiskers have been confirmed by experiments.
Gold Nanodot whisker
A group of researchers have nanoengineered a structure comprising an array of more than about 1000 nanowhiskers on a substrate in a predetermined spatial configuration. It can be used as a photonic band gap array wherein each nanowhisker is located within a distance from a predetermined site not greater than about 20% of its distance from its nearest neighbour, according to an U.S. patent application.
To produce the array, an array of masses of a catalytic material are positioned on the surface, heat is applied and materials in gaseous form are introduced so as to create a catalytic seed particle from each mass, and to grow, from the catalytic seed particle, epitaxially, a nanowhisker of a predetermined material, and wherein each mass upon melting, retains approximately the same interface with the substrate surface such that forces causing the mass to migrate across said surface are less than a holding force across a wetted interface on the substrate surface.
A nano imprint lithography (NIL) process produces the required nanostructure formations. The length of the nanowhiskers may be as long as required, such as more than 1 micrometer that permits nanostructures of arbitrary depth to be formed.
Gold dots of approximately 125 nm diameter and 45 nm thickness can be seen on the substrate surface Although the growth of nanowhiskers catalyzed by the presence of a catalytic particle at the tip of the growing whiskerAtoms that are added to the tip of the whisker as it grows diffuse through the body of a solid catalytic particle or diffuse along the surface of the solid catalytic particle to the growing tip of the whisker at the growing temperature. The nanowhiskers can also be used in a light emitting diode (LED).