SECONDARY-ION PRODUCTION BY ELECTRON AND ION-BOMBARDMENT OF ALKALI-HALIDES

We have investigated desorption of positive and negative ions for elec tron and ion bombarded NaCl single crystals. Our experiments include t he first systematic measurements of electron-stimulated desorption of negative ions from an electron irradiated (100) surface of NaCl. Measu rements of the mass distributions and relative yields of emitted parti cles indicate that during electron bombardment, positive ions are form ed by gas-phase ionization of neutral atoms and molecules by primary a nd secondary electrons. In contrast, electron desorbed negative ions a re created by direct emission of Cl- from the surface due to electroni c processes. A mechanism of ion formation during keV, heavy ion bombar dment is discussed in terms of an Auger process and/or direct emission of lattice ions from a collision cascade.