>SiO2- and CuO-enhanced growth of Ge–Si1−xGexOy and GeO2–Si1−xGexOy core–shell nanowires on a Si substrate via carbothermal reduction
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 GeO2core inside the Si1−xGexOy shell on Si and SiO2/Si substrates are discussed, respectively.
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