The growth of porous ZnO nanowires (NWs) via phase transformation of ZnS NWs at 500–850 °C in air was studied. The ZnS NWs were first synthesized by thermal evaporation of ZnS powder at 1100 °C in Ar. On subsequent annealing at 500 °C in air, discrete ZnO epilayers
formed on the surface of ZnS NWs. At 600 °C, polycrystalline ZnO and the crack along the (0001) interface between the ZnO epilayer and ZnS NW were observed. At 700–750 °C ZnS NWs transformed to ZnO NWs, meanwhile nanopores and interfacial cracks were observed in the ZnO NWs.
Two factors, the evaporation of SO2 and SO3 and the stress induced by the incompatible structure at the interface of ZnO epilayer and ZnS NW, can be responsible for the formation of porous ZnO NWs from ZnS NW templates on annealing at 700–750 °C in air. Rapid
growth of ZnO at 850 °C could heal the pores and cracks and thus resulted in the well-crystallized ZnO NWs.
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