Valence band photoelectron spectroscopy as a probe of the surface chemistry associated with corrosion and its prevention

The paper gives an overview of the use of valence band photoemission, with emphasis on the use of X-ray Photoelectron Spectroscopy (XPS), to study the surface chemistry of systems where corrosion is a serious issue, and methods for corrosion protection involving the use of protective films. The information provided by the technique is discussed, together with illustrations of the application of calculation approaches to predict the appearance of the spectra. The valence band of metals and of oxidized species (including discrete ions such as sulfate, carbonate and phosphate) is discussed. The ability of the technique to distinguish between closely related oxidized species is illustrated with reference to various examples. The application of angle resolved valence band spectra is reviewed. Examples are provided from the author's work. An approach where the surface chemistry can be controlled by conducting the chemistry in an anaerobic electrochemical cell is also described. This approach is shown to have the ability to produce surfaces with a novel chemistry by reacting the clean metal surface prepared under ultra-high vacuum conditions with liquids with and without electrochemical control. Examples of oxide-free phosphate films on various metals is presented.