Charge transfer electronic effects on chemically modified Mo(100) surfaces

The surface Mo atom oxidation states for a series of chemically modified Mo(100) surfaces have been measured by XPS. The surface adsorbates used were boron, carbon, oxygen and carbon monoxide. For partially oxidized Mo(100) surfaces, a range of oxidation states (1.2 to 4.0) are observed for the coverage range 0.3 to 1.4 ML of oxygen. The results suggest that an atomic oxygen chemisorbed phase exists at coverages below one monolayer. Above one monolayer, a surface oxide layer is formed. Surface modification by near monolayer amounts of boron, oxygen, carbon and a mixed oxy-carbon adlayer showed that the Mo oxidation states are linearly dependent on the adatom electronegativity. Linearity implies a direct relation between the extent of charge transfer from the metal and the modifier electronegativity. The presence of electronically deficient acidic surface sites on chemically modified Mo(100) is demonstrated by the XPS core level shifts.