QUANTUM FORMALISM FOR ELECTRON-CAPTURE FROM A SOLID-SURFACE BY HEAVY PROJECTILES MAKING GRAZING COLLISIONS

Electron capture from surfaces by grazing heavy projectiles is studied with a fully quantum treatment. The collision is considered in the high-energy regime where the projectile velocity is larger than the Fermi velocity of the free-electron gas of the solid. Some approximations commonly used in atomic collision theory, such as the first-order Born, the impulse, and the Vainstein-Presnyakov-Sovelman approximations, are adapted to the present geometry and interactions. The surface-electron and surface-projectile interactions are represented according to the jellium model and the Moliere and Lindhard potentials. Detailed calculations are made for protons on an Al(111) surface and compared with recent experiments. No agreement is found; the theory largely underestimates the experiments at high energies. This disagreement shows that the high-energy-tail data cannot be explained as a capture process from the free-electron gas. Other neutralization mechanisms should take place to account for the experiments.