We compared positron- and electron-stimulated desorption (e+SD and ESD) of positive ions from a TiO2(110) surface. Although desorption of O+ ions was observed in both experiments, the desorption efficiency caused by positron bombardment was larger by one order of magnitude than that caused by electron bombardment at an incident energy of 500 eV. e+SD of O+ ions remained highly efficient with incident positron energies between 10 eV and 600 eV. The results indicate that e+SD of O+ ions is predominantly caused by pair annihilation of surface-trapped positrons with inner-shell electrons. We also tested e+SD from water chemisorbed on the TiO2 surface and found that the desorption of specific ions was enhanced by positron annihilation, above the ion yield with electron bombardment. This finding corroborates our conclusion that annihilation-site selectivity of positrons results in site-selective ion desorption from a bombarded surface.

We have observed positron-stimulated ion desorption from a TiO2(110) surface. H+ and O+ ions were desorbed at incident positron energies above the desorption thresholds for electron impact. However, only O+ ions were detected at energies below those thresholds. These results suggest that by surface ionization positron annihilation as well as by positron impact leads to the O+ ion desorption. By contrast, it is likely that the H+ ions are not desorbed by positron annihilation, but rather by impact ionization.