Recent developments in electron and photon stimulated desorption

Abstract

The realization by Knotek and Feibelman that core ionization can be an important primary mechanism in electron stimulated ionic desorption (ESID) from oxides, and the availability of synchrotron radiation as excitation source for detailed photon stimulated ionic desorption (PSID) studies, have stimulated a number of interesting experiments in the last two years. It is shown that—besides direct valence excitation—adsorbate core ionization is a new channel for ESID and PSID from covalent adsorbates on metals also, while metal core ionization rarely or never causes desorption in such systems. However, detailed threshold studies and comparison to Auger yields show that this cannot be simply explained by treating the core ionization/Auger decay sequence as a composite Franck–Condon transition to multiply valence ionized states. Rather, strong influences of many-body interactions (e.g., shake ups) exist. This is not the case for ionic surface species; in these cases PSID can be used as species-specific EXAFS probe. The investigation of desorption of neutrals, which constitute the overwhelming majority of products at low energies, shows that neutrals can be formed by reneutralization of ions. Additional channels exist below the absolute ionic thresholds; core ionization is not an important primary channel for neutrals production. The consequences of these findings are discussed in context with existing models.