An XPS and TPD study of gold oxide films obtained by exposure to RF-activated oxygen

Low-temperature oxidation of the polycrystalline surface of bulk metallic gold with radio-frequency activated oxygen is used to obtain oxide films, which are investigated by a combination of X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). The XPS estimate for the composition and thickness of the oxide films is close to Au₂O₃ and is 6-10 nm. The analysis of the Au4f and O1s lines reveals only one state of the oxidized gold, which is described by E_b(Au4f) = 85.5 eV, and two nonequivalent states of oxygen with E_b(O1s) = 529.3 eV and 530.3 eV, which are uniformly distributed over the oxide film and may be attributed to nonequivalent oxygen states in the gold oxide structure. The thermal stability study shows that the gold oxide decomposes in one stage into metal at a temperature of T_des = 530 K. According to the TPD data, the desorption activation energy is E_des = 140 kJ/mol. The high-temperature oxidation of the gold surface reveals the formation of dissolved oxygen in bulk gold. This oxygen is characterized by a broad TPD peak with a maximum at T_des = 800 K. This oxygen state is not detected by XPS. The concentration of dissolved oxygen is supposed to be below the XPS sensitivity threshold and is estimated at about 1% or less.