Field Ion Microscope Studies of Interactions Between Atoms Adsorbed on Tungsten (110) Surfaces

Field ion microscope studies of lateral interactions between adsorbed atoms using transition metals as model adsorbates are described. Interaction energies determined for adatoms on nearest-neighbor adsorption sites on tungsten (110) surfaces are generally small but depend on adsorbate electron configuration. Dissociation energies for such adatom dimers decrease from >60 kJ mole-1 for Ta2 to approximately zero for Re2, and rise to 15 kJ mole-1 for Pt2. Low dimer stability is considered to reflect the nonadditivity of bonding involving the substrate conduction electrons. Long-range interaction between rhenium adatoms due to indirect coupling via the substrate was explored by determining the pair distribution, but it is not considered that the expected oscillatory character of the interaction has been demonstrated conclusively.