Raman spectroscopic studies of Ni-W oxide thin films

We report on a Raman spectroscopic study of sputtered nickel-tungsten oxide films. Their crystallographic and chemical identification with electrochemical lithium insertion and extraction are obtained by Raman spectroscopy. The Raman spectra of as-deposited Ni-W oxide films show a strong peak at 525 cm(-1) due to vibrations of the Ni-O bonds and two weaker peaks at 875 and 950 cm(-1), which we attribute to the vibrations of the W-O bonds. The Raman spectrum of the as-deposited Ni-W oxide film shows a blueshift of the Ni-O stretching mode compared to that of a NiOx film. When lithium ions and electrons are inserted, the overall Raman intensity increases due to electrochromic bleaching and the relative intensity of the peak at 875 cm(-1) also increases. By comparing these results with results from the same measurements using sodium ions, we conclude that this reversible peak at 875 cm(-1) is not directly related to the Li or Na ions. (C) 2001 Published by Elsevier Science B.V.