Detection of low levels of oxygen in reactive materials by x-ray photoelectron spectroscopy (XPS)

Accurate detection of low levels of elements such as carbon and oxygen by ion beam sputtering techniques is complicated because those elements (as well as hydrogen) are the primary constituents of the residual gas molecules present in ultrahigh vacuum systems. In this paper, we determine the minimum exposure of titanium to vacuum is only 0.1 langmuir (1 L = 10⁻⁶ Torr s) before detectable levels of adsorbed oxygen artificially raise the measured concentration. Despite this limited analytical window, oxygen detection limits of 0.3-0.4 atom% can be achieved by x-ray photoelectron spectroscopy. We apply similar approaches to aluminum nitride and titanium nitride thin films grown by atomic layer deposition techniques to show best practices for detecting low levels of carbon and oxygen. A linear relationship between exposure and oxygen adsorption at exposures < 4 L was observed for all materials studied.