Formation of potentially protective oxide-free phosphate films on titaniumcharacterized by valence band x-ray photoelectron spectroscopy

This paper reports the results of a continuing study focused on preparing n ovel surface chemistries on metal surfaces. In this paper we report how it is possible to prepare oxide-free titanium metal surfaces protected by a fi lm consisting of phosphate. The surface is prepared by electrochemical trea tment in an anaerobic cell which allows electrochemistry to be conducted on samples located in a vacuum system attached to an x-ray photoelectron spec trometer. When a clean metal surface is subjected to electrochemical treatm ent in aqueous orthophosphoric acid an oxide-free phosphate film can be for med on the metal which is stable on subsequent air exposure. Compositional variations were found with potential and other factors. Identical electroch emical treatment of as-received titanium metal yielded samples that had a s urface consisting largely of oxide. The chemical composition of these surfa ce films was studied by core level and valence band x-ray photoelectron spe ctroscopy. Valence band photoemission interpreted by band structure calcula tions was found to be especially effective in understanding subtle differen ces in surface chemistry, enabling the clear identification of phosphate (b eing able to distinguish between orthophosphate and metaphosphate films) an d its distinction from surface oxide. Valance band spectra calculated from band structure calculations for TiO, Ti2O3, TiO2, TiC, TiPO4, and TiP2O7 ar e reported. (C) 2001 American Vacuum Society.