Water-vapor-enhanced growth of Ge–GeO_xcore–shell nanowires and Si_1−xGe_xO_ynanowires

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.