XPS studies of low-temperature plasma-produced graded oxide-silicate-silica layers on titanium

A method has been developed to produce a silica coating bonded to an oxidized titanium substrate, graded in composition and structure through the surface layer, providing the base for deposition of bioactive glasses and hydroxyapatite. A low-temperature air/water/tetraethoxysilane plasma coating method is reported. Characterization of the graded surface layer using XPS and SEM is compared with previously reported studies of similar layers on nickel substrates. Depth profiling and the modified Auger parameter were used to elucidate the structure of the interphase region between the titanium and silica. A functionally-graded layer, from the titanium metal through the oxide, orthosilicates, pyrosilicates, chain silicates and layer silicates to bulk silica, was demonstrated. The thickness of the layer was in the range 30-50 nm, depending on the duration of oxidation and tetraethoxysilane deposition. (C) 1998 John Wiley & Sons, Ltd.