IONIZATION IN THE SPUTTERING PROCESS - THE EFFECT OF THE LOCAL-STRUCTURE IN THE TIGHT-BINDING APPROXIMATION

The ionization probability of atoms during a sputtering event is calculated in the scope of a one-electron description, in which the emitted particle is issued from an atomic cluster which describes the ejection site immersed in the continuum of a metal substrate. This calculation, carried out in a semi-classical approach, requires the knowledge of the local electronic structure of the cluster atoms and the determination of the matrix elements of the evolution operator associated to the sputtered particle. The later is obtained in the short memory approximation and local densities of states are approximated by a continued fraction description of the local Green's functions in the frame work of the tight-binding approximation. This model allows the study of different geometrical and chemical configurations for the emission site, such as step sites and/or presence of impurity atoms in the direct vicinity of the emitted secondary ion. Relative results are presented for different models for the particle trajectory for which time dependence of coupling parameters on the ionization probability are examined.