ANGLE-RESOLVED PHOTOEMISSION-STUDY OF THE CLEAN AND OXYGEN-COVERED NBC(110) SURFACE

Angle-resolved photoemission spectroscopy utilizing synchrotron radiation has been used to study the electronic structure of a NbC0.95(110) clean surface and the surface exposed to oxygen at room temperature. The spectra for the clean surface show that the bulk band emissions show small hnu-dependent dispersions at hnu = 27.5-65 eV, thus the density of state effect is dominant in the photoemission process at this photon energy range. A surface state is found to be formed on this surface at 1.7 eV at the GAMMABAR point. The state is attributed to a Tamm state pulled off from the SIGMA3 bulk band. As the oxygen is adsorbed on the (110) surface, the O 2p-derived states are formed at 4.7 and 6.5 eV for 5-10 L exposure. The inner valence C2s band emission is strongly affected by oxygen adsorption, indicating that the oxygen atom sits on the surface carbon atoms.