Substrate effects on the structural and photoresponse properties of CVD grown ZnO nanostructures: alumina vs. silica

ZnO nanowires (NWs) have been grown using the Chemical-Vapor-Deposition (CVD) method on two different substrates, SiO2 and Al2O3. Striking differences have been observed between products. First, while only (0001) oriented NWs are found in SiO2 grown samples, m plane-oriented nanostructures have been observed for alumina substrates. Second, Au catalytic interdiffusion is evidenced in NWs grown on SiO2, whereas for the NWs grown on alumina the Au catalytic remains at the tip. The origin of the differences in morphology and catalytic location is discussed, with the help of detailed Transmission Electron Microscopy analyses, in terms of growth mechanisms and segregation of the Au particle influenced by the substrate nature and crystallinity. Finally, we show the consequences of such effects in the photoresponse of nano-detectors based on the studied nanowires.