Direct mapping of adatom-adatom interactions

The dependence of pair interactions at a metal surface upon interatomic distance as well as orientation has for the first time been explored by mapping out the two-dimensional distribution function for two metal atoms at equilibrium on W(110). Observations with the field ion microscope have been made for the pairs Re-Pd, W-Pd, and Ir-Ir. For all these interactions are highly anisotropic, with repulsion along [11{}0] and [001], but long-range oscillatory attraction along [11{}1]. This anisotropy is consistent with elastic calculations; the observed decay of attractions is not.