Coadsorption of oxygen and cesium on ZrC(1 1 1)

Interaction of Cs and oxygen on the ZrC(1 1 1) surface at room temperature has been investigated by core-level photoemission spectroscopy and X-ray absorption spectroscopy utilizing synchrotron radiation. Oxygen adsorbs dissociatively on the Cs-covered surface, and the dissociated O atoms interact directly with the substrate Zr atoms beneath the Cs overlayer. The O atoms are also bound to the Cs atoms so that the Cs cations are formed. However, there is no spectroscopic evidence for the formation of Cs oxides such as Cs2O, Cs2O2 and CsO2. Although oxidation of the ZrC bulk does not proceed, a part of the Zr atoms in the substrate surface becomes highly charged cations, which cannot be obtained when the clean ZrC(1 1 1) surface is exposed to O2 at room temperature.