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Metallic NbSe2 nanotubes and nanofibers

Synthesis of transition metal oxide and metallic nanowires has shown way to yield materials with more complicated phenomena such as Ferro electricity, thermoelectricity, and superconductivity. NbSe2 nanoscale materials are one such case. Elements in niobium diselenide are Nb 37.04 %, Se 62.96 %.
Synthesis methods
NbSe2 nanotubes and nanofibers can be synthesized by chemical vapor transportation method by a nearly equilibrium reacting process. Both of their structures have a similar size of 100–200 nm in diameter. Nanotubes consist of rolled-up NbSe2 layers and nanofibers are a pile of thin flat layers. The mechanism of the formation of NbSe2 nanotubes and nanofibers can be thought of as being on the basis of deseleniditive transition from an NbSe3 fiber-shaped crystal. The electrical resistance of the nanofibers measured with conductive atomic force microscopy show metallic behavior at room temperature.Nanotubes of NbSe2 in admixture with nanorods can be produced by the thermal decomposition of NbSe3 and have outer diameters in the 35–100 nm range, with lengths in excess of several hundred nanometers. The nanostructures are metallic and become superconducting at 8.3 K.
High-purity Nb and Se are used as starting materials and mixed in a stoichiometric ratio and allowed to react with each other at 800° C. or less in a vacuum with a temperature gradient of 1 k/cm. Solution-based methods have advantages over solid-state methods to synthesize nanomaterials as they show low reaction temperatures, have size-selective growth; and morphological control. The characteristic length scales for superconductivity in NbSe2 are less than 10 nm. Solution-based synthesis of 2D nanoplates and 1D nanowires of NbSe2 give high yield starting from a niobium chloride precursor and elemental Se.
Using NbSe2 as starting material nanofibers or nanotubes can be prepared by a chemical transport process using aniodine acting as a medium. When C60 is used as a promoter to act as nuclei, nanofibers or the nanotubes can be efficiently produced. The process of formation is that initial nanoparticles surrounding a C60 molecule form nanorings and grow into the nanotubes. Other nanoparticles surrounding no C60 molecule grow into the nanofibers with a diameter of 150 nm and a length of 10 μm. To date, one dimensional NbSe2 nanostructures have been prepared by the intense electron irradiation of bulk NbSe2, by thermal decomposition of NbSe3 in a flow of argon at 700 deg.C, and by chemical vapor transport with elemental Nb and Se in an evacuated silica ampule at 800 deg C. Disadvantages of these approaches include low yield, low purity, and a broad size distribution of product.
According to researchers of University of California, production of NbSe2, (niobium diselenide) nanotubes can be done by high doses of electron irradiation in an apparatus where irradiation is 2 MeV in a Van de Graaff accelerator. Well defined nanotubes of several nm long and few nm wide, which are presumably hollow, and capped at one end can be produced. The irradiation conditions can be: voltage 1.3 MeV, current 5μA, dose rate 25 kGy/min, and total dosage 1000 kGy. According to researchers of Northwestern University, NbSe2 nanostructures can be formed in a one-pot reaction followed by thermal decomposition at high temperatures. They added in a typical reaction, 20 mL of degassed oleylamine (dodecylamine) to the mixture of NbCl5 (1mmol) and Se (2 mmol) under N2, vigorously stirring reaction mixture while heating at 280 deg C for 4 h, during which the precursors dissolves and forms a black suspension. This air-stable intermediate is extracted and washed repeatedly with hexane, dried under vacuum, and heated at 450 deg C for 3 h under a N2 atmosphere to form different morphologies of NbSe2 nanostructures by quenching the hot reaction mixture at different temperatures.
One report indicates that NbSe2 fibers with diameters of 80-160nm can be synthesized by the thermal decomposition of NbSe3 obtained from the reaction of Se and Nb in airtight vessel.Niobium diselenide particles are in the form of flake, pieces, chunk, lump and ingot. Niobium diselenide (NbSe2) is sometimes used as a lubricant at high temperatures. It does not break down at temperatures up to about 1300°C and has superconductivity.

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