Exit angle dependence of charge-state distribution of backscattered He ions

Exit angle and energy dependences of the charge-state distribution of backscattered He ions were investigated when 500 keV He+ ions were incident on SiO2. The energy dependence of the He+ fraction was estimated by comparing the measured He+ spectra with the simulated spectra of He ions in all charge states at the exit angles of 5–25° with respect to the SiO2 surface. We found that the He+ fraction is almost independent of the exit angle at energies higher than 250 keV and the observed energy dependence of the He+ fraction is in good agreement with that for the carbon-foil-transmission experiment. In the low energy region (<250 keV), however, the He+ fraction decreases as the exit angle decreases.