Oxygen adsorption on a Mo2C(0001) surface : Angle-resolved photoemission study

Oxygen adsorption on a C-terminated alpha-Mo2C(0001) surface has been investigated with Auger electron spectroscopy, low-energy electron diffraction, and angle-resolved photoemission spectroscopy utilizing synchrotron radiation. It is found that the oxygen atoms adsorb on the Mo atoms in the second layer forming a (1 x 1) orthorhombic periodicity. The oxygen adsorption induces a peculiar state around the Fermi level, which is observed at 0.4 eV in the normal-emission spectra. ARPES measurements show that the state is a partially occupied metallic state. The photoionization cross section of the state shows a maximum at the photon energy of 56 eV, which is assigned as originating from the resonance of the Mo 4d photoemission involving Mo 4p - > 4d photoexcitation.