Phase evolution in annealed Ni-doped WO3 nanorod films prepared via a glancing angle deposition technique for enhanced photoelectrochemical performance

Ni-doped WO3 nanorod films were fabricated via a reactive magnetron cosputtering with a glancing angle deposition technique. The crystal structure and surface morphology were observed using grazing incident X-ray diffraction and field emission Scanning Electron Microscopy, respectively. The chemical compositions and oxidation state of each element were investigated by X-ray photoemission spectroscopy. The local structure and phase evolution were investigated via X-ray absorption spectroscopy. The local structure of Ni atoms in WO3 nanorod films is characterized as a NiWO4 nanocluster in the WO3 matrix, which is supported by calculated spectra. The phase information obtained after annealing demonstrates that short-length order in amorphous transitions to crystallinity. The phase information of the local structures were acquired and discussed as well as the effect on the annealing process. The coupling of amorphous WO3, crystalline WO3, and amorphous NiWO4 exhibits high photoelectrochemical activity of the sample annealed at 400 ?, which was observed with a large current density (2.35 mu A/cm(2)) at 1.20 V vs. Ag/AgCl under visible light irradiation, which is greater than that of the unmodified WO3 photoelectrode (1.38 mu A/cm(2)).