On the dynamics of secondary-electron and anion emission from an Al/O surface

Kinetic energy distributions and absolute yields of negative oxygen ions and secondary electrons resulting from positive ions impacting an aluminum surface have been determined as a function of the oxygen coverage of the surface, The experiments have been carried out with positive sodium ions at collision energies below 500 eV. Both the negative ion and secondary electron yields are observed to be strongly dependent on the oxygen coverage of the aluminum surface. The kinetic energy distributions of the dominant negative ion, O-, peak at approximately 1.0 eV and have a significant high-energy tail. The secondary electron kinetic energy distributions peak between 0.8-1.0 eV, have widths of 1.0-1.5 eV and exhibit no features indicative of discrete spectra. For both the ions and the electrons, the most probable kinetic energy is essentially independent of the impact energy and there is no correlated electron-anion emission. A mechanism is proposed to augment the collision cascade in order to model the sputtering of O- and the emission of electrons. Finally, the secondary processes are investigated with a partial coverage of sodium which serves to reduce the surface work function. (C) 1997 Elsevier Science B.V.