ATOMIC BINDING OF TRANSITION METALS ON CLEAN SINGLE-CRYSTAL TUNGSTEN SURFACES

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 fielddesorption properties of adatoms on the (110) plane are discussed in terms of its anomalous work function.