OXIDATION OF NB(001) STUDIED BY HIGH-RESOLUTION CORE-LEVEL PHOTOEMISSION

Using high-resolution core-level photoemission with synchrotron radiat ion, we observed two suboxide states on the Nb(001) surface, which was heated in 1 x 10(-6) Torr O-2 for several hours and then annealed sev eral times at high temperatures in an ultrahigh-vacuum condition. Thes e suboxide states were identified as Nb2O and NbO from the Nb3d(5/2) c ore-level photoemission spectra. The relative amounts of these suboxid e states varied with the annealing temperature, showing that at progre ssively higher temperatures more oxygen-deficient oxides were produced . Meanwhile, LEED patterns of the complex superstructures of the oxidi zed surfaces also changed. Many of these findings are analogous with o ther oxidized refractory metals.