The Dynamics of Ion-Solid Interactions: A Basis for Understanding SIMS

Abstract

A fundamental understanding of the SIMS process requires first a knowledge of how the nuclear positions of the atoms or molecules in the sample change with time in response to the impact of the primary ion. Secondly, a quantitative description of the ionization processes is required for those species which leave the sample surface as ions and are subsequently detected by the mass spectrometer. Both of these tasks are exceedingly complex to treat theoretically, given the large number of perturbed particles and the tremendous range of kinetic energies and subsequent ejection mechanisms that need to be considered. For example, in Fig. 1a is shown a model microcrystallite of Cu(OOl) about to be struck by a 600 eV Ar⁺ ion at normal incidence. From the results of the classical dynamics calculations we have been exploring, the state of the crystallite after the last Cu atom has left the surface is shown in Fig. 1b. Note that virtually every atom has moved from its original position after a time of only 194 fsec (1.94 × 10–13 sec). In addition, the kinetic energy of the atoms in the solid varies from nearly 0 to as high as 250 eV.