Template assisted nanowire growth process involves various steps. A template is created for nanowires to grow within. Due to anodization alumina (Al2O3) is formed and because of aluminum’s unique property, self organized pore arrays are formed with very high aspect ratios. Pore filling and formation of nanowire is achieved by various physical and chemical deposition methods. In fact pore diameter and pore packing densities are a function of acid strength and voltage adopted in the anodization step. Al2O3 template preparation is due to anodization of aluminum and starts with uniform layer of ~1mm Al. Al serves as the anode, Pt may serve as the cathode, and 0.3M oxalic acid is used as the electrolytic solution and 40V is applied. This is a low temperature process (2-5C). Anodization time is a function of sample size and distance between anode and cathode.

Key Attributes of the process indicate that pore ordering increases with template thickness and pores are more ordered on bottom of template. Process always results in nearly uniform diameter pore, but not always ordered pore arrangement. Aspect ratios are reduced when process is performed when in contact with substrate (template is ~0.3-3 mm thick). Electrochemical deposition method works well with thermoelectric materials and metals and the process allows to remove/dissolve oxide barrier layer so that pores are in contact with substrate. Filling rates of up to 90% have been achieved.

Silicon nanowire CVD growth process is done with Fe/SiO2 gel template. Here a mixture of 10 sccm SiH4, 100 sccm helium at 500C and 360 Torr and deposition time of 2h are adopted. Straight wires of diameter ~ 20nm and length ~ 1mm can be formed.With Au-Pd islands, mixture of 10 sccm SiH4, 100 sccm helium at 800C and 150 Torr and deposition time of 1h are adopted to form amorphous Si nanowires. In the process decreasing catalyst size improves nanowire alignment wnd the product is 30-40 nm diameter and length ~ 2µM.

In the synthesis of nucleation by TiSi2 islands on Si, the process is done with SiH4/SiH2Cl2 at 6400C – 6700C for 395 s. By this method mostly curved wires with a mixture of wires branched along their length and also straight wires of nearly 25 nm in diameter and approximately 1.3 mm long are obtained.

In the Vapor-Liquid-Solid (VLS) based reaction with Au as catalyst, Au/Si molten alloy balls nucleate and grow to a specific size while transition to Si nanowire growth occurs. In this process SiH4 is diluted to 10% in He flowing at 40 sccm at a pressure range of 0.1–10 Torr and temp range of 320–700C. Here the product wire quality is best in lower pressure/higher temperature range and wire diameter obtained is as thin as 10nm.For the template-assisted, Au nucleated Si nanowires, gold is evaporated (Au nanodots) into thin ~200nm alumina template on silicon substrate. Reaction with silane will yield desired results.