A Study of Nanophase Tungsten Oxides Thin Films by XPS

Abstract

Nanophasic tungsten oxides thin films have been deposited at 500 °C on quartz and glass substrates starting from W(CO)6 using the metal organic chemical vapor deposition technique (MOCVD). Two series of deposition experiments were carried out to make a comparison between the results obtained employing, as reactant gases, O2 mixed with water vapor and a dry mixture of N2 with 25% H2, respectively. The obtained tungsten oxides were analyzed by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) in order to investigate their microstructure, chemical composition, and surface morphology. In this work, XPS analyses of two tungsten oxides thin films deposited in different atmospheres are presented. Besides the wide scan spectra, charge corrected binding energies for the W 4f7/2, W 4f5/2, O ls, and C 1s surface photoelectron signals are reported. In particular, the film obtained in H2 atmosphere shows the presence of W in an oxidation state lower than VI.