Crystalline nanostructures, such as nanotubes and nanowires, offer unique access to low-dimensional physics (effects such as electron tunnelling, Coulomb blockade, size effects on the thermal conductivity, and so on), and they can be used as nanotechnology building blocks to reach higher device integration densities than conventional fabrication methods. They can function both as devices and as the wires that access them. In particular, silicon nanowires are particularly attractive due to the central role of the silicon semiconductor industry, which would allow silicon nanowires to be implemented using existing technologies.
Processes for Synthesizing Silicon Nanowires - CVD, PECVD, Laser-Ablation and Evaporation
Different methods have been used to synthesize silicon nanowires:
• Chemical Vapor Deposition (CVD),
• Plasma Enhanced CVD (PECVD),
CVD does require the use of a metal catalyst, but this allows controlled, selective growth by prepatterning the metal on the substrate. This method is often based on the vapour-liquid-solid idea in which various metals, such as gold, iron, titanium and gallium, catalytically enhance the growth of silicon wires.
Using Low Pressure Chemical Vapour Deposition (LPCVD) to Synthesize Silicon Nanowires on Gold Ultrathin Films
In the Materials and Microsystems Laboratory at the Polytechnic of Torino, some attempts were done for the synthesis of silicon nanowires on gold ultrathin films by Low Pressure CVD (thermal decomposition of silane at temperature ranging at 500-550 °C, pressure 5 Torr). Micro-Raman spectroscopy shows a crystalline phase for the wires and an amorphous silicon coating at the bottom of the structure. Work is in progress for the synthesis of ordered nanowires grown on gold nanodots patterned on silicon substrates by e-beam lithography.