Hot-carrier transport processes in stimulated desorption of alkali halides

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Abstract
Electron- and photon-stimulated desorption of epitaxial thin films and bulk single crystals of alkali halides has been investigated. It has been found that the widely accepted model based on self-trapped exiton decay and thermally activated defect diffusion cannot account for a number of experimental observations. In particular, it cannot explain the stability of the very thin alkali-halide films against the electron beam, and it fails to interpret correctly the yield dependence of the halogen atoms emitted with nonthermal energies on the film thickness and sample temperature. It is shown that for satisfactory interpretation of those data one has to take into account early stages of crystal excitation, i.e., hot carrier formation and transport processes occurring prior to self-trapped exciton phase. Consequently, a comprehensive description of the observed desorption features is presented.