Vertically aligned ZnO nanowires (NWs) were grown on Au-nanocluster-seeded amorphous SiO _2 films by the advective transport and deposition of Zn vapours obtained from the carbothermal reaction of graphite and ZnO powders. Both the NW volume and visible-to-UV photoluminescence ratio were found to be strong functions of, and hence could be tailored by, the (ZnO+C) sourceSiO _2 substrate distance. We observe C flakes on the ZnO NWs/SiO _2 substrates which exhibit short NWs that developed on both sides. The SiO _2 and C substrates/NW interfaces were studied in detail to determine growth mechanisms. NWs on Au-seeded SiO _2 were promoted by a rough ZnO seed layer whose formation was catalysed by the Au clusters. In contrast, NWs grew without any seed on C. A correlation comprising three orders of magnitude between the visible-to-UV photoluminescence intensity ratio and the NW volume is found, which results from a characteristic Zn partial pressure profile that fixes both O deficiency defect concentration and growth rate.
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