The energy spectrum of sputtered atoms II

Publisher Website
Google Scholar
Abstract
An investigation of the phenomenon of sputtering has been carried out using the forward form of the Boltzmann transport equation with the surface conditions devised by Thompson (1968). In this way an exact solution for the emergent energy spectrum has been obtained as a function of energy and direction of the incident beam. By appropriate averaging over energy the sputtering yield and efficiency are obtained for projectiles which are identical with the atoms of the host medium. The energy spectrum, yield and efficiency so calculated are compared with the same quantities obtained using the infinite-medium approximation. Significant differences are found in the energy spectrum, particularly at energies well in excess of the surface binding energy. The sputtering yield shows a maximum as a function of incident angle at around 85° to the normal. This is in general agreement with experiment and indicates that the model is a reasonable one. The infinite-medium approximation also exhibits a maximum, but for different reasons, and it varies much more rapidly with incident angle than does the half-space result. The sputtering efficiency increases monotonically with incident angle, the maximum being at grazing incidence. The average energy of emitted particles has been examined as a function of angle and it has been possible to distinguish between projectiles re-emitted and sputtered recoil atoms. The average energy of the recoil atoms emitted is very much less than that of the projectiles. Explanations are advanced for these effects. Throughout the calculations it is assumed that the transport mean free path is energy independent and a special approximation for the scattering kernel, which allows an analytical solution to be obtained, is used. The limitations of these approximations are discussed and the effect on the results indicated.