Chemical design of inorganic nanowires, nanotubes and nanowire networks

Abstract

Inorganic nanowires are expected to play a central role in the re-engineering of products with applications in composites, thin films, nanodispersions, energy conversion devices, sensors, nanoelectronic devices and optics. The synthesis of materials at the nanoscale might also help in the discovery of new phases with interesting properties. However, the synthesis strategies for inorganic nanowires is quite limited and have not reached the level of maturity needed for either bulk manufacturing or for controlling nanowire characteristics such as sub 10 nm diameters and different growth directions. In this regard, we report several synthesis strategies that potentially offer in-situ control over the resulting nanowire characteristics such as size, growth direction and an ability to form two-dimensional networks. The techniques described here could be scaled up easily for bulk production of various nanostructures. Our preliminary results suggest that the nanowires form stable dispersions in both organic and aqueous solvents compared to nanoparticles of the same material. INTRODUCTIONIn the last few years, the synthesis of inorganic nanowires and nanotubes has gained tremendous importance for several reasons 1 (a) the availability of nanowires allows for rapid experimental understanding of the physics and chemistry of materials under reduced dimensions; 2 (b) the synthesis of materials at the nanometer scale could lead to the discovery of new phases through their structural variations, for example -nanotubes; 3 (c) the availability of nanowires and nanotubes in large quantities could allow for bottom-up assembly techniques for several engineering application areas such as composites, electronics, catalysts and optics; 4 and (d) the possibility of growing perfect crystals at the nanoscale. However, the nanowire quantities required for particular applications vary. These requirements range from bulk quantities for composites and thin films to single wires for sensors and electronic devices to large area arrays for field emission based applications. The growth of one-dimensional crystals in the form of micron-scale whiskers has been known for several decades starting in 1940s 5 and was formalized as the Vapor-Liquid-Solid method in 1964. 6 More recently in 1991, a similar strategy was employed to discover the growth of carbon nano-tubular structures. 7The vapor-liquid-solid (VLS) method employs catalyst clusters to template one-dimensional growth. In the VLS technique, a vapor phase solute is selectively dissolved into metal droplets, and it precipitates one-dimensionally due to the metal droplet size confinement. Recognizing the fact that one can reduce the resulting wire size by reducing the metal droplet size, several researchers sought different ways of creating smaller clusters and providing solutes using different means. The notable techniques involved laser ablation of solid targets containing metal catalysts, 8 thermal chemical vapor deposition 9 over catalyst cluster dispersions on supports and gold clusters dis...

Growth of platelike and branched single-crystalline Si3N4 whiskers

“…Si 3 N 4 nanorods [5][6][7] have been synthesized by mild benzene-thermal route [5], carbothermal reduction [6] and template method [7]. Si 3 N 4 nanowires [8][9][10][11][12][13][14][15][16][17] have been synthesized by carbothermal reduction and nitriding reaction at high temperatures [8][9][10][11][12][13], combustion under a high N 2 pressure [14], hot-filament CVD and microwave plasma heating method [15][16][17]. Most recently, Si 3 N 4 nanobelts have been synthesized via a vapor-solid thermal reaction between ammonia and silicon monoxide [18].…”