A near ambient pressure XPS study of Au oxidation

Abstract

The surface of a gold foil under ozone oxidation was examined by near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and scanning electron microscopy (SEM). Our in situ observations show that a surface oxide phase is formed during the exposure to ozone; however this phase decomposes under vacuum and even in the presence of ozone at temperatures higher than 300 °C. Assuming that an oxide overlayer completely covers the Au surface, the thickness of the oxide phase was estimated to be between 0.29 and 0.58 nm by energy-dependent XPS depth profiling. The surface oxidation led to structural modifications of the gold surface. These morphological changes do not disappear even under vacuum. In the Au 4f spectra, an additional component at low binding energy (83.3 eV), which appears during/after O₃ treatment, is assigned to the presence of low-coordinated atoms which appear on the Au surface as a result of surface restructuring under oxidation. Ex situ SEM images demonstrate that only the region of the sample that was exposed to O₃ shows the presence of ridges on the Au surface.