A comparison of electron-stimulated desorption of halogen atoms from different alkali-halide single-crystals

Abstract

Kinetic energy distributions of halogen atoms emitted due to electron-stimulated desorption (ESD) were measured for a (100) surface of NaCl-type alkali-halide crystals (NaCl, NaI, NaF, KCl, KBr, KI, RbCI, RbBr, RbI) under the same experimental conditions. It was found that energy spectra of halogen atoms emitted from potassium and rubidium chlorides, bromides, and iodides, kept at temperatures below 250°C, consist of two components: the thermal (Maxwellian) peak and the higher energy peak (at about 0.25 eV) whose energy is temperature-independent. From the energy spectra and complementary total yield measurements relative desorption rates for both thermal and nonthermal components were determined for all investigated samples. The results are compared with predictions of the Rabin-Klick criterion and the self-trapped exciton relaxation energy calculations by Song et al. Finally, it is shown that the hyperthermal halogen emission could be well correlated with a measure of the excess space between the neighboring halogen ions in the lattice. This correlation is consistent with the recently proposed concepts of ESD from alkali halide surfaces.

Key Words:

• desorption
• alkali halides
• electron bombardment
• surfaces