X-ray photoelectron spectroscopic study of the oxidation of polycrystalline rhenium by exposure to O2 and low energy O2+ ions

X-ray photoelectron spectroscopy has been used to study the interaction of O2 and low energy O2+ ions with polycrystalline rhenium. The results indicate that rhenium oxides cannot be obtained at temperatures below 630 K even for very high O2 exposures at low pressures or by low energy O2+ implantation. It has been observed that upon exposure to oxygen the oxygen atoms incorporate into the near surface region of the metal up to 17 atom% (i.e., ReO0.2) by a non-thermally activated process, at least for temperatures below 630 K. At higher exposures and more markedly at high temperatures a suboxide labelled as ReO forms at the surface up to coverages of ≈0.7 monolayers (ML). Bombardment with low energy O2+ ions caused a higher incorporation of oxygen atoms up to 30 atom% (ReO0.45), but in no case an oxidation state higher than Re2+ was detected. In addition it is shown that the full width at half maximum (FWHM) of the Re 4f peak can be used to determine the oxygen incorporated into the Re (i.e., ReOx) during the initial steps of the oxidation process, where no appreciable chemical shifts are observed.