Properties of ultrathin layers of palladium on a tungsten {110} surface

The growth mode, structure, thermal stability and work function of Pd films up to several monolayers in thickness on a W{110} surface are studied. At room temperature, layer-by-layer growth occurs, at least up to 4 layers. Layers in excess of the first monolayer are metastable and agglomerate at substrate temperatures above 700 K. Pd-W and Pd-Pd interactions within the first layer are investigated with thermal desorption techniques. The binding energy for single Pd atoms to the substrate is 3.6 eV/atom, the energy per lateral bond between nearest Pd atoms is about 0.05–0.12 eV/bond dependent upon range of interaction. These data are based on a phase transition occurring during the desorption of the first layer. The desorption of Pd in excess of the first monolayer is similar to the sublimation of bulk Pd.