Geometrical and surface effects in the sputtering process

A semiempirical model of the sputtering process [S. A. Schwarz and C. R. Helms, J. Appl. Phys. 50, 5492 (1979)] is reexamined in light of subsequent developments. In this model, the energy dependence of the sputtering yield results from a geometrical effect, in contrast to the common approximation in which this dependence is determined by the stopping power of the incident atom. A direct comparison may now be made with recent stopping-power formulas, Monte Carlo simulations, and experimental data. Monte Carlo results in the literature suggest a material dependence of the sputtering yield which is inherent in the geometrical model and absent in the stopping-power approximation. The surface escape probabilities derived from this model also show a material dependence, and an inverse correlation with positive ion yields, which cannot be solely attributed to surface binding energies or oxygen contamination.