Electron-stimulated desorption of iodine atoms from KI(100): An energy- and temperature-dependent study

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 velocity 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 versus incident electron energy indicate a threshold of approximately 5.5 eV. The data collectively indicate that ESD of KI involves exciton decay at the surface. The temperature and pulse-width dependencies of the thermal component are consistent with decay of bulk self-trapped excitons, thermally assisted H-center diffusion and trapping at metastable defects.