Adsorption of O2 on polycrystalline rhenium metal at room temperature studied by synchrotron X-ray photoemission spectroscopy

Abstract

Abstract Clean rhenium (Re) surfaces were made by sputtering and annealing in UHV. The clean surfaces were then exposed to O2 in the pressure range of 10−8 (1 L) to 5 Torr (∼1.5×107 L) at room temperature. The surface that was exposed at 5 Torr O2 was also annealed at several temperatures. Core level spectra of the Re 4f and O 1s were acquired at photon energies of 200 and 790 eV, respectively, from clean, O2 exposed, and annealed surfaces. At least two components, approximately 1.4 eV apart, can be identified in the O 1s spectra. One is attributed to atomic oxygen, and the other to molecular oxygen. At least two new features appear in the Re 4f spectra after the clean surfaces were exposed to O2, and they may correspond to surface Re atoms surrounded by different numbers of oxygen. Annealing the O2 exposed surfaces results in rearrangement of surface oxygen. Although equilibrium thermodynamic calculations predict that Re2O7 is the most stable phase in the O2 pressure and temperature range used in the exposure experiments, no appreciable Re oxide was observed, suggesting that the oxidation of Re metal is controlled by kinetics rather than thermodynamics.