No abstract

No abstract

X-ray photoelectron spectroscopy (XPS) has been used to investigate the electrochemical and thermal oxidation of titanium nitride (TiN) coatings prepared by physical vapour deposition (PVD) at 200OC. Electrochemicpl oxidation of TiN was carried out at various potentials in phthalate buffer solution (pH 5.0). Evaluation of the XPS Ti 2p and N 1s spectra showed the presence of nitride, oxynitride and oxide species in the layer formed by anodic oxidation. The electrochemical oxidation of TiN to TiO, proceeds through the formation of a mixed oxynitridel oxide layer, which transforms into oxide (TiO,) at sufficiently positive potentials (E > 1.1 V vs. SHE). The oxidation of TiN to TiO, is accompanied by the formation of molecular nitrogen (N,). The thickness of the oxide layer reaches -7 nm after oxidation at the highest potential (1.9 V). A complete coverage of the TiN surface by TiO, leads to an anodic peak in the polarization curve. On the basis of angleresolved XPS measurements, two types of oxynitride species are identified, which are distributed differently throughout the oxidized layer.X-ray photoelectron spectroscopy depth profiles of TiN oxidized at 450OC and 600OC in an oxygen flow reveal that at the lower temperature an oxynitride layer is formed, whereas a thick TiO, layer appears on top of TiN at the higher temperature. The interface between the nitride and oxide phases is relatively sharp. It is suggested that the mechanism of TIN oxidation proceeds by a progressive replacement of nitrogen by oxygen. The TiN coatings can be used up to 600 "C as a protective coating in an oxygen atmosphere.Valance band spectra of TIN, as well as of electrochemically and thermally oxidized TiN, are presented and discussed.

No abstract

No abstract