Efficient and surface site-selective ion desorption by positron annihilation

We compared positron- and electron-stimulated desorption (e(+)SD and ESD) of positive ions from a TiO(2)(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 TiO(2) 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.