Auger, resonant, and plasmon-assisted charge-transfer processes in atom-surface collisions

The Keldysh Green's-function formalism is used to evaluate the atomic occupation number of a projectile colliding with a metal surface. This formalism has an advantage that allows us to handle simultaneously Auger, resonant, and plasmon-assisted exchange processes along;with the interference between them. A time-dependent Hamiltonian containing Anger-like and resonant like terms, and the electron-electron Coulomb potential in the solid, is proposed. The atomic self-energies are calculated up to a second order in the interaction potential. An effective resonant amplitude is defined, and Auger self-energies are presented where the plasmon-assisted processes are included through a surface response function. Finally, some numerical results for a proton colliding with an Al surface by using a simplified description of the solid response function are presented, where an analysis in terms of the incidence angle and the energy level is shown.