High aspect-ratio semiconducting ZnO nanowires formed by anodic oxidation of Zn foil and thermal treatment

Arrays of zinc oxide (ZnO) nanowires with diameter of about 200 nm and length of >20 µm were successfully obtained by simple anodic oxidation of Zn foil in sodium bicarbonate electrolyte and thermal post-treatment. The as formed anodic film consists of overlapping nanowire bundles forming a flower-like or grass-like structure. Thermal annealing in air at temperatures higher than 150 °C results in the conversion of initially formed hydroxycarbonate precursor to crystalline wurtzite ZnO. The crystallinity of ZnO nanowires increases with increasing annealing temperature. On the other hand, optical band-gap energy of obtained semiconducting nanowires was found to be independent of the temperature applied during the thermal treatment. It is expected that the described method can be further scaled up and offers a great potential even for technological applications.