Optical radiation from low-energy hydrogen atomic and molecular ion-surface collisions

Abstract

The energy and oxygen-pressure dependence of Balmer radiation photon yield due to ion-surface collisions on polycrystalline molybdenum using hydrogen atomic and molecular ions were measured in the energy range from 200 to 10 keV. These results, obtained under ultrahigh-vacuum conditions, provide new information on the ways in which the photon yield is produced by electronic interactions of the emerging particles with the surface. Radiation yield, normalized to current and backscatter yield, varied in a consistently exponential manner over the entire incident-ion energy range. The molecular state and the charge state of the incident particles were measured to have no discernable effect on the final excitation for clean surfaces. At partial pressures of oxygen below ${10}^{\ensuremath{-}11}$ Torr, surface concentrations of oxygen below 2% of a monolayer on molybdenum could be maintained during the experiments. Increased surface coverages (up to 0.5 to 1 monolayer) raised the photon yield for molybdenum by a factor of 7. These oxygen-dependent effects are tentatively interpreted as owing mainly to changes in the deexcitation probability in the vicinity of the surface.