Fig. 3. (a) Zn 2p and (b) Cu 2p XPS spectra of ZnO/CuO nanowires and (Cu, Zn)O nanowires. (c) Surface Cu ratio of the nanowires as a function of CuO shell thickness. For ZnO/CuO nanowires, the CuO shell thickness is 10 nm and oxygen plasma treatment is performed prior to measurement. For (Cu, Zn)O nanowires, the CuO shell thickness is varied in the range of 3–20 nm. ‘NWs’ represents ‘nanowires’.
