Formation and decomposition of gold oxides prepared by an oxygen-dc glow discharge from gold films and studied by X-ray photoelectron spectroscopy

Abstract

Formation and decomposition of thin (<1 nm) gold oxides prepared by an oxygen-dc glow discharge from gold films were studied by X-ray photoelectron spectroscopy (XPS). Four oxygen species comprising O 1s components Ⅰ, Ⅱ, Ⅲ, and Ⅳ are present in the XPS spectra. Component Ⅳ appears in the early formation periods and then changes into the oxide component Ⅲ. Components Ⅰ and Ⅱ are both stable at high temperatures and assigned to hydroxyl groups. The angular dependence of the XPS spectra of the gold oxides indicates that the oxygen species of components Ⅰ and Ⅱ are present in this order from the top surface of the gold oxide (component Ⅲ). The gold oxides decompose after 36 h at room temperature and decompose immediately at temperatures exceeding 121 °C in a dark atmosphere. The oxides also decompose under ultraviolet (UV) light irradiation at 254, 302, and 365 nm and decompose more rapidly at the shorter wavelengths. The decomposition of the gold oxides under UV light irradiation is slower in a high vacuum but is faster in a water vapor atmosphere. The decomposition caused by UV light irradiation and its wavelength dependence indicate reaction of the gold oxides with excited water molecules produced by UV light absorption.