Threshold effects and time dependence in electron-and photon-stimulated desorption

Abstract

The use of optical techniques to study the dynamics of neutral alkali emission from alkali halides in electron- and photon-stimulated desorption (ESD/PSD) has produced significant new insights into the ways in which incident electronic energy is converted into kinetic energy of desorbing neutral atoms. In this paper, we show that the threshold for efficient PSD of Li from LiF lies below the band-gap energy, lower than those obtained from earlier ESD threshold measurements on NaCl. Time-resolved measurements of ground-state and excited-state Li desorption from LiF under both electron and photon irradiation exhibit a clear distinction between the spatial and physical origins of these two desorption products. The data suggest a possible identification of excited-state neutral desorption with surface-specific processes; one the other hand, a defect-diffusion model for ground-state desorption is more consistent with the data than are earlier thermal drift models. We also discuss briefly the implications of this work for technological problems as diverse as high-power laser optical damage and the production of intense lithium ion beams for fusion applications.