Dependence of alignment and orientation induced by grazing-incidence and beam-foil electron-exchange interactions on surface electronic structure

Abstract

We report first detailed measurements of the effect of adsorbates on final configuration of electrons after electron pickup by positive ions during grazing-incidence and beam-foil interactions. Positive hydrogen ions incident at grazing angles on metal surfaces are neutralized and coherently excited due to anisotropic electron pickup from the surface. As a result the emitted radiation is strongly circularly polarized and when the scattered ions pass through an external electric field, the Stokes parameters characterizing the polarization oscillate as a function of the electric field strength. These oscillations, quantum beats, arise from quantum mechanical phase interference between participating atomic states. The effect of surface modification on these quantum beats is studied by adsorbing oxygen onto the surface. In addition, we discuss the alignment induced by interactions of a 17 keV H + beam passing through thin carbon foils with and without a deposited layer of lithium. The results presented here demonstrate the sensitivity of these techniques to the influence of overlayers on surface conditions and support the idea that future experiments with detailed surface characterization could provide a basis for theories of the sensitivity of electron pickup to surface electronic structure.