Origin of H− in collisions of hydrogen atoms with an adsorbate-covered Cu(100) surface

Abstract

Results are presented from an experimental study of electron capture and loss during collisions of low-energy hydrogen atoms and ions with a residual gas covered metal surface. Ground-state hydrogen atoms (H1s) and the atomic ions (H−,H+) were scattered from a Cu(100) surface with energies ranging from 25to200eV. Energy loss analysis indicates that the dominant process leading to H− formation proceeds directly through the adsorbed vacuum species, with the metallic crystal acting primarily as a physical scattering platform. In addition, ion beam experiments reveal effects due to the charge state of the incident particle that are inconsistent with the results expected for clean metal surfaces. Measurements indicate that the neutralization of incident ions as expected for clean metals is suppressed, a feature that is attributed to the band gap and dielectric strength of the adsorbed layer.