The synthesis of transition metal silicide and germanide nanostructures within the solution-based solvent vapour growth system

This thesis describes the use of the solution-based solvent vapour growth (SVG) system in the synthesis of transition metal germanide and silicide nanostructures, as well as the use of transition metal silicide nanowire arrays as high surface area current collectors for lithium ion battery applications. The growth of nickel monogermanide (NiGe) nanowires directly from Ni foil, within the SVG system, is presented in Chapter 3. The evolution of nanowire growth from the Ni substrate was studied and it was found that the Ge precursor thermally decomposes to form a rough nickel germanide layer on the Ni substrate, from which NiGe nanowire growth subsequently occurs. Investigations into the use of thin Ni films as the growth substrates were conducted and showed that when thin nickel films were used, germanium nanowire growth occurred through the established vapor-solid-solid growth mechanism. Chapter 4 focuses on the effect of Si precursor decomposition on the formation of copper silicide nanostructures on Cu. By increasing the reactivity of the Si precursor used, through the addition of a reducing agent, the reaction temperature required for the synthesis of copper silicide (Cu15Si4) nanowires was decreased by over 100 °C to 350 °C. At elevated temperatures (≥ 400 °C), it was observed that the enhanced reactivity of the silicon precursor resulted in the formation of unique nanostructures of the more Si rich copper silicide phase, Cu3Si. In Chapter 5, the development of a novel one-step synthetic approach to the synthesis of nickel silicide and axial heterostructure nickel silicide-silicon (NixSi-Si) nanowires, within the SVG system, is described. Growth of these nanowires was achieved by growing gold seeded silicon nanowires on nickel substrates using iv the established solution-liquid-solid mechanism. The high temperature used for silicon nanowire growth allowed nickel to diffuse into the silicon nanowire from the substrate and for in situ silicidation of the silicon nanowire to occur. In Chapter 6, the use of copper silicide (Cu15Si4) nanowire arrays as high surface area current collectors for silicon lithium ion battery anode applications is outlined. Amorphous Si films were deposited onto pre-formed Cu15Si4 nanowire arrays and planar copper substrates prior to electrochemical testing. Electrochemical testing revealed markedly improved capacity retention values for the Cu15Si4 nanowire arrays compared to those seen for amorphous Si deposited on planar Cu substrates.