Negative ionization of the secondary ions of silver and gold sputtered from their elemental surfaces

Calculations of the ionization probabilities of Ag− and Au− particles, ejected during sputtering of clean Ag(1 0 0) and Au(1 0 0) surfaces, respectively, are reported. An effective one-electron theory is used to describe: the plane metal surface, with a projected band gap, the secondary emitted atom, whose charge state is investigated, and its nearest-neighbor substrate atom, put in motion by the collision cascade generated by the primary ion beam. Suitable rectilinear trajectories are selected to describe the motion of these two atoms outside the solid. A good agreement is found with van Der Heide's experiments (P.A.W. van Der Heide, Nucl. Instr. and Meth. B 157 (1999) 126).