Atomic Binding of Transition Metals on Clean Single-Crystal Tungsten Surfaces

Abstract

The binding energy of single atoms of the Period-6 transition elements on atomically perfect single-crystal planes of tungsten was measured by utilizing low-temperature-pulse field desorption, in a ultrahighvacuum field-ion microscope. For any given adatom, the dependence of the binding energy on surface crystallography was observed to be inconsistent with a pairwise interaction model. A new model incorporating a surface-charge redistribution into a pairwise potential is shown to be consistent with the data. The variation in binding energy with electronic configuration of the adatom is interpreted in terms of an electron-energy band model. The binding energy depends upon the electron occupancy of two subbands assumed to exist in the d levels of the atom, when it is adsorbed on the surface. Finally, the abnormal field-desorption properties of adatoms on the (110) plane are discussed in terms of its anomalous work function.