Excited-state formation as ${\mathrm{H}}^{+}$ and ${\mathrm{He}}^{+}$ ions scatter from metal surfaces

Impact of 10- to 30-keV ${\mathrm{H}}^{+}$ or ${\mathrm{He}}^{+}$ ions on polycrystalline metal surfaces causes some projectiles to be backscattered in a neutral excited state. These projectiles subsequently radiatively decay, emitting Doppler-broadened spectral lines. By analysis of the spectral shape of these lines, we are able to determine the probability of radiationless deexcitation of the excited backscattered atoms. Quantitative measurements of spectral intensity indicate that less than 1% of all projectiles are backscattered in an excited state. The relative variation of total spectral line intensity with angle of projectile incidence and with projectile primary energy has been successfully predicted using a model which assumes that the probability for excited-state formation is independent of the scattered projectile's energy and direction. We also predict the variation in total spectral line intensity with target atomic number. Finally, we examine briefly the sputtering and excitation of Al under ${\mathrm{He}}^{+}$ impact.