ELECTROCHEMICAL AND THERMAL-OXIDATION OF TIN COATINGS STUDIED BY XPS

X-ray photoelectron spectroscopy (XPS) has been used to investigate th e electrochemical and thermal oxidation of titanium nitride (TiN) coat ings prepared by physical vapour deposition (PVD) at 200 degrees C. El ectrochemical oxidation of TiN was carried out at various potentials i n phthalate buffer solution (pH 5.0). Evaluation of the XPS Ti 2p and N 1s spectra showed the presence of nitride, oxynitride and oxide spec ies in the layer formed by anodic oxidation. The electochemical oxidat ion of TiN to TiO2 proceeds through the formation of a mixed oxynitrid e/oxide layer, which transforms into oxide (TiO2) at sufficiently posi tive potentials (E > 1.1 V vs. SHE). The oxidation of TiN to TiO2 is a ccompanied by the formation of molecular nitrogen (N-2). The thickness of the oxide layer reaches similar to 7 nm after oxidation at the hig hest potential (1.9 V), A complete coverage of the TiN surface by TiO2 leads to an anodic peak in the polarization curve. On the basis of an gle-resolved XPS measurements, two types of oxynitride species are ide ntified, which are distributed differently throughout the oxidized lay er, X-ray photoelectron spectroscopy depth profiles of TiN oxidized at 450 degrees C and 600 degrees C in an oxygen flow reveal that at the lower temperature an oxynitride layer is formed, whereas a thick TiO2 layer appears on top of TiN at the higher temperature. The interface b etween the nitride and oxide phases is relatively sharp. It is suggest ed that the mechanism of TiN oxidation proceeds by a progressive repla cement of nitrogen by oxygen. The TiN coatings can be used up to 600 d egrees C as a protective coating in an oxygen atmosphere. Valance band spectra of TiN, as well as of electrochemically and thermally oxidize d TiN, are presented and discussed.