PARTICLE EJECTION FROM ION-BOMBARDED CLEAN AND REACTED SINGLE-CRYSTAL SURFACES.

A model based on a classical dynamical calculation of the impact of a 600-eV Ar** plus ion into a single crystal has been developed to the point where it compares quantitatively to a wide variety of experimental observables. Here, we make direct comparisons between experiment and theory for relative sputtering yields, energy and angular distributions of the ejected atoms, and multimer yields. The model is also extended from clean single-crystal surfaces to include adsorbate atoms and molecules. These results are compared to experimental SIMS studies aimed at sorting out the structure-sensitive factors that contribute to the cluster ion yield. In oxygen chemisorption on Ni(100), for example, the O//2** minus /O** minus yield is four times larger for a c (2 multiplied by 2) coverage than for a p (2 multiplied by 2) coverage, a value also predicted by the calculations. In molecular CO chemisorption, the ejection of CO is found to occur molecularly in both the experiments and in the calculations. In comparison to the calculations, a high value of Ni//2CO** plus /NiCO** plus is consistent with a bridge-bonded CO structure at low coverage.