No abstract

The effects of a SiO2 layer grown on a Si substrate and the CuO additive in GeO2 powders for the enhanced growth of Ge–Si1−xGexOy and GeO2–Si1−xGexOy core–shell nanowires (hereafter referred to as Ge–Si1−xGexOy and GeO2–Si1−xGexOy nanowires, respectively) via carbothermal reduction at 1050–1100 °C in flowing Ar were studied. Using GeO2 powders as the feedstock alone, nanowires having a composition of Ge–Si1−xGexOy were grown on a SiO2/Si substrate, whereas the same nanowires could not be grown on a Si substrate. Adding CuO into GeO2 powders enhanced the growth of GeO2–Si1−xGexOy and Ge–Si1−xGexOy nanowires on the Si substrate as well as that of GeO2–Si1−xGexOy nanowires on the SiO2/Si substrate. The crystal growth mechanism seems to follow the vapour–solid process. The present study reveals that the oxidation of the Si substrate plays an important role in enhancing the growth of Ge–Si1−xGexOy and GeO2–Si1−xGexOy nanowires via carbothermal reduction of GeO2 powders. The mechanisms for the precipitation of the Ge or GeO2 core inside the Si1−xGexOy shell on Si and SiO2/Si substrates are discussed, respectively.

Si 1−x Ge x O y nanowire (SiGeONW) assemblies with cord-, chain-, and tubelike morphologies were grown on a Si substrate via the carbothermal reduction of GeO 2 /CuO powders at 1100°C in Ar. The growth of various SiGeONWs assemblies follows the vapor-liquid-solid process. The CuSiGe droplets formed during the growth of SiGeONWs simultaneously play the roles of catalyst and reactant. The morphology of SiGeONWs assemblies is not temperature controlled but dependent on the Cu concentration and the size of CuSiGe catalysts. This phenomenon is unlike the Geand Ga-catalyzed growth of SiO x nanowire assemblies. In addition, the processing parameters and the mechanisms for the growth of SiGeONWs assemblies with various morphologies are discussed.

The effects of moist Ar on the growth of Ge–GeOx core–shell nanowires (Ge–GeOx NWs) and Si1−xGexOy nanowires (SiGeONWs) on Si substrates without adding a metal catalyst via the carbothermal reduction of GeO2 powders at 1100 °C were studied. No significant nanowires were grown in dry Ar at a flow rate of 100–300 sccm until a bit of water in the range of 0.5–2 ml was loaded into the furnace. More water suppressed the growth of nanowires because of the exhaustion of more graphite powder. The growth of Ge–GeOx NWs and SiGeONWs follows the vapor–solid and vapor–liquid–solid processes, respectively. The present study showed that the water vapor serves as an oxidizer as well as a reducer at 1100 °C in enhancing the growth of SiGeONWs and Ge–GeOx NWs, respectively. The growth mechanisms of Ge–GeOx NWs and SiGeONWs are also discussed.