PNNL

Abstract

We have studied the electron-stimulated desorption (ESD) of neutral atomic iodine from single crystals of KI(100) using time-of-flight laser resonance enhanced multiphoton ionization spectroscopy and quadrupole mass spectrometry. The measured iodine velocty distributions have thermal and non-thermal components. The yield of the thermal component increases with increasing substrate temperature, whereas the yield of the non-thermal component decreases slightly with temperature. The ESD rate for the thermal component decreases with increasing pulse-width, unlike the rate for the non-thermal component, which is independent of pulse-width. Measurements of ESD yields vs. incident electron energy indicate a threshold of ~5.5 eV. The data collectively indicated that non-thermal ESD of KI involves exciton decay at the surface. The temperature and pulse-width dependence of the thermal component is consistent with thermally assisted decay of bulk self-trapped excitons, H-center diffusion and trapping at metastable defects.