Interaction of Ag with MgO(100)

The electronic and chemical properties of Ag clusters on MgO(100) films grown on Mo(100) were studied using metastable impact electron and ultraviolet photoelectron spectroscopies (MIES/UPS) and temperature programmed desorption (TPD). The work function of the as-grown and vacuum-annealed MgO(100) surfaces increases monotonically with increasing Ag coverage. In contrast, an initial decrease of the work function upon Ag deposition was found for the sputter-damaged MgO(100) surface, implying that small Ag clusters on this surface are electron deficient. Point defects with high electron affinities, such as F²⁺ and/or V/V^- centers, created by sputtering are believed to be responsible for the initial decrease of the work function upon Ag deposition. For low Ag coverages, the quantity of CO adsorbed at 80 K on a sputter-damaged MgO(100) surface is much greater than that adsorbed for a comparable Ag coverage on a relatively smooth, MgO(100) surface. These results are consistent with point defects on MgO(100) being responsible for altering the electronic and chemical properties of supported Ag clusters.