In this work, Silicon nanowires (SiNWs) have been synthesized under systematically varied growth conditions and their effects on the morphology, structural and chemical perfections of the NWs were studied.

The solid-liquid-solid (SLS) and vapour-liquid-solid (VLS) routes were employed for the synthesis of the SiNWs. Using the SLS approach, a layer of catalyst was coated onto the Si substrate by sputtering and SiNWs were grown on the catalyst-coated substrate using heat treatment in a furnace at inert gas environment and at high temperatures. For the VLS approach, SiNWs were synthesized by Chemical Vapour Deposition (CVD) using Si-supported Au nanoclusters as catalyst and silane (SiH 4 ) gas reactants in hydrogen as the vapor phase precursor. The temperature and total gas pressure during growth are carefully selected on the basis of bulk Au-Si binary phase diagram in order to achieve various growth stages for the study. Other growth methods like self-selective electroless etching and galvanic displacement were also studied for the synthesis of SiNWs and metal-Si core-shell structures. Large-area vertically aligned silicon nanowire arrays have been successfully synthesized in an aqueous solution containing AgNO 3 and HF using high-grade silicon substrate. Metal-Si core-shell heterostructures were subsequently obtained by galvanic displacement of SiNWs in an acidic HF electrolyte containing the metal ions.

Lattice image (from HRTEM) of the section of the NW showing single crystalline Si core and amorphous SiO x sheath

The morphology, chemistry, microstructure and crystallography of the resulting SiNWs and core-shell structures have been investigated using conventional and high-resolution transmission electron microscopy (CTEM & HRTEM), scanning electron microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX) and X-ray diffractometry (XRD). Critical growth parameters were established for the synthesis of SiNWs with optimal structural and chemical properties. A combination of single-crystalline, polycrystalline and amorphous SiNWs and core-shell structures have been obtained.