Determination of the concentration of surface hydroxyl groups on metal oxide films by a quantitative XPS method

Quantitative XPS has been used to determine the surface concentration of hydroxyl groups in native air-formed oxide films on metals having low surface areas. A mathematical expression has been derived to give the concentration of surface hydroxyl groups as a function of the intensity ratio of the OH to O2− contributions to the O 1s photopeak. This expression is based on modeling the oxide film on a metal to be a multilayer system consisting of an outermost layer of organic contamination, a layer of chemisorbed water, a surface hydroxylated region of the oxide film and the inner portion of the oxide film. The average values of the experimentally determined concentrations of surface hydroxyl groups are 15, 13, 11, 6 and 8 OH nm−2 for oxide-covered aluminum, chromium, titanium, tantalum and silicon, respectively. X-ray photoelectron spectroscopy depth profiles using argon ion sputtering and variable-angle XPS have been utilized in this work. Surface treatments have employed either ultrasonic cleaning with organic solvents or argon plasma treatment. © 1998 John Wiley & Sons, Ltd.