Observation of ion desorption from MgO(001) by electron bombardment

Electron (E < 1 keV) stimulated desorbed positive ions (H+, H2+ and O+) from a MgO(001) surface are observed by means of a quadrupole mass analyser (QMA) and by Time-of-Flight (TOF) methods. The desorbed oxygen ions have two different kinetic energies, 7.8 and 4.6 eV. The origin of the ions with the lower energy is identified as adsorbed species which are ionized by electron bombardment (from examining experimental results). The total yield of oxygen ions rises above energies of 80 eV for the primary electron beam. This threshold energy of 80 eV corresponds to the core-hole creation energy in the 2p state of Mg2+. The desorption of the faster oxygen ion is explained by the Knotek-Feibelman mechanism of the electronic transitions following core-hole creation in the Mg2+ ion. (author)