Desorption kinetics of Li-atom delayed emission from LiF under low-energy-electron bombardment

Publisher Website
Google Scholar
Abstract
Electron-stimulated desorption of lithium atoms from LiF crystals has been investigated with quadrupole mass spectroscopy at temperatures in the range 350 to 440 °C. Following the cessation of electron bombardment, a delayed maximum in the emission of lithium atoms is observed. In a previous publication, this surprising result was explained in terms of a homogeneous nucleation of large clusters (colloids). The diffusion of F centers was neglected, because the diffusion time was considered to be much shorter than the lifetime of the colloids. In this paper we report on studies that use undoped LiF and LiF doped with divalent impurities in order to test the homogeneous-nucleation model and to investigate the details of the behavior of the cluster centers responsible for the occurrence of the delayed maximum. Our results suggest that the formation of small F-center agglomerates (not large Li colloids) during bombardment along with F-center diffusion are the important factors which account for the delayed emission of Li atoms. Based on our results, we suggest a modified model that incorporates diffusion, and a heterogeneous-nucleation picture in which small F-center clusters with widely varying thermal stabilities form and decay at impurity sites.