Exposure of Oxidized Copper Surfaces to Aqueous Na[sub 2]S Solution Studied with Soft X-Ray Spectroscopy

We present results from X-ray absorption spectroscopy ͑XAS͒ and resonant inelastic X-ray scattering ͑RIXS͒ of oxidized polycrystalline copper surfaces ͓Cu͑I͒ and Cu͑II͒, respectively͔ exposed to a 1.0 mM aqueous solution of Na 2 S ͑sodium sulfide͒ for several hours.Scanning electron microscopy reveals that the Cu oxide surfaces attain a much rougher texture upon sodium sulfide exposure, and that the exposed Cu͑II͒ oxide sample exhibits areas with crystallites.The XAS spectra show that sodium sulfide effectively reduces Cu͑II͒ oxide to Cu͑I͒ compounds.The RIXS spectra of the exposed surfaces closely resemble those of the Cu 2 O reference sample with the notable exception of their Cu L III,II -RIXS spectra.We conclude that copper evidently forms a Cu͑I͒ compound with oxygen but with a Cu 3d-band of much reduced width, pointing to the possibility of a more complex compound containing both oxygen and sulfur.