ESD thresholds for NaCl

Abstract

Energy thresholds of electron stimulated desorption (ESD) for thin NaCl layers relative to the target current onset are measured. The applied procedure allows to correct electron beam energy for the contact potential difference in the system. The measured threshold energies are about 16.8 and 21 eV for Cl +. For Na +, Na and Cl the threshold energies are about 8.4 and 16.8 eV. The value of 8.4 eV coincides with the fundamental absorption edge and confirms the so-called “defect-mediated desorption” model of ESD. Basing on the experimental fact that the fundamental absorption edge appears to be a common threshold for different particles it is suggested that the near surface lattice instabilities induced by electronic transitions may result in a direct ejection of the constituents as well. The 16.8 eV threshold for Cl + confirms the involvement of an Auger transition in positive halogen ion emission. The 21 eV threshold is assigned to the shake-up/shake-off processes.