ATOMIC INTERACTIONS ON CRYSTALS - A REVIEW OF QUANTITATIVE EXPERIMENTS

Two types of studies have been pursued to gain insights into atomic interactions at crystal surfaces. Changes in macroscopic surface properties, such as atom desorption as a function of coverage, have been interpreted in terms of the forces operating between atoms. Recently the ability to observe individual atoms on solids, available through several techniques, has also made it possible to directly measure energy changes when two or more atoms are brought together. For adsorbed metal atoms, both approaches have yielded quantitative results, and these are summarized, with special emphasis upon results from direct observations in the field ion microscope. The latter have revealed several interesting trends: a significant dependence upon the orientation of the atom pair, interactions extending over very long distances (> 10 angstrom), and sizable contributions from many-atom effects.