Surface Investigation of Intermetallic PdGa(1̅ 1̅ 1̅)

The intermetallic PdGa is a highly selective and potent catalyst in the semihydrogenation of acetylene, which is attributed to the surface stability and isolated Pd atom ensembles. In this context PdGa single crystals of form B with (-1-1-1) orientation were investigated by means of XPS, UPS, STM, XPD and LEED to study the electronic and geometric properties of this surface. UPS and TDS were accomplished to probe the chemisorption behavior of CO. The PdGa(-1-1-1) surface exhibits a (1x1) LEED and a pronounced XPD pattern indicating an unreconstructed bulk-truncated surface. Low temperature STM reveals a smooth surface with a (1x1) unit cell. No segregation occurs and no impurities are detected by XPS. The electronic structure as well as the CO adsorption properties reveals PdGa(-1-1-1) to be a bulk-truncated intermetallic compound with Pd-Ga partly covalent bonding