The energy spectrum of sputtered atoms

Using a simple, hard-sphere model of scattering the emergent flux and current of particles emitted from a surface during bombardment with a monoenergetic beam of particles has been calculated. Analogous results are obtained when the source of particles is uniformly distributed in the half-space. This situation represents essentially an idealized sputtering problem. The calculations have been made in order to test the current theories in which the half-space nature of the problem is neglected and replaced by an infinite medium with appropriately chosen sources or, in some cases, by the infinite medium solution itself. It is found, in agreement with the suggestions of previous workers, that the current methods tend to overestimate the sputtered fraction at low energies. A quantitative survey is made of this overestimate. In addition, the solutions of the infinite medium approximation are examined. It is shown that a careful application of this approximation can lead to satisfactory agreement with the exact solution for low energies but that significant deviations remain. (author)