Ionization probability of sputtered atoms

The ionization probability of atoms sputtered from metal surfaces is discussed with the use of an approach of Blandin, Nourtier, and Hone. A general expression is obtained for this probability for the case in which the energy position of the sputtered-atom valence level has a linear dependence on distance and the atom velocity is constant. A limiting form of this expression was given by Brako and Newns; this limiting form is very useful in analyzing the higher-velocity part of the data obtained by Yu for O^- sputtered from transition-metal surfaces. Analysis of the lower-velocity part of the data proceeds by the combination of the more general formulation of the theory with a very simple trajectory determined on the basis of a Morse-potential interaction between the sputtered adatom and the substrate atom which strikes it. A good account of Yu's experimental data is obtained with the use of parameter values determined solely from measurements and calculations of the ground-state properties of oxygen adsorbed on metal surfaces.