The role of exciton diffusion in the electron induced sputtering of alkali halides

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Abstract
Exciton diffusion allows excitons created some distance beneath the surface to contribute to sputtering and causes the sputtering efficiency to peak at a higher bombarding electron energy than would be expected if no diffusion occurred. Measurements of this peak energy for KI and KI containing 0.1% Tl indicate exciton diffusion ranges 21 and 13 nm. In KI:Tl a reduction in sputtering efficiency and a lower peak energy are consistent with the model of exciton diffusion, the Tl+ ions acting as recombination centres. The exciton trapping cross section of thallium ions which can be estimated in this model is comparable with the ionic size of Tl+.