Electron-stimulated desorption of positive ions from hexagonal α-SiC

Abstract

Electron-stimulated desorption (ESD) of positive ions (H +, O +, +OH, F + and Cl +) from the Si- and C-terminated surfaces of hexagonal α-SiC has been observed for electron energies in the 5–105 eV range. Comparison of these results with those for the ESD of the same ions from the surfaces of Si and condensed hydrocarbons leads to a model for the H +, +OH, F + and Cl + threshold desorption process based on transitions from deep valence Si and C “s-like” levels to states in the conduction band, followed by Auger decay to form a localized multiple valence-hole configuration. O + desorption, on the other hand, is initiated by O 2s ionization. Evidence is found for a strong dependence of the F + threshold on the local chemical bonding. The results indicate that the thresholds for ESD of these ions from SiC are determined more by the electronic excitation of the substrate than by direct excitation of the adsorbate bond.