Kinetic electron emission in the interactions of slow ions with MgO surfaces P. Riccardi a,b, * , P. Barone a , A. Bonanno a , A. Oliva a , P. Vetro ` a , M. Ishimoto b,c , R.A. Baragiola b a Laboratorio IIS, Dipartimento di Fisica, Universita ´ della Calabria, and INFM Unita ` di Cosenza, 87036 Arcavacata di Rende, Cosenza, Italy b Laboratory for Atomic and Surface Physics, University of Virginia, Charlottesville, VA 22904, USA c Fujitsu Laboratories Ltd., Akashi, Hyougo 674-8555, Japan Abstract We report experimental energy distributions and yields of electrons emitted from MgO surfaces under the impact of slow noble gas and sodium singly charged ions at varying incident energies. At impact energies below 1 keV, electron spectra are nearly independent of ion type and energy. A tail of high- energy electrons is observed to grow at higher impact energies. The results are explained in terms of promotion of oxygen-2p electrons during binary projectile-oxygen collisions populating continuum and excitonic states. Excitons can significantly contribute to electron emission due to the nega- tive electron affinity of the surface. Ó 2005 Elsevier B.V. All rights reserved. 1. Introduction Ion-induced electron emission from solids is due to the two main processes of potential and ki- netic electron emission [1,2]. In potential electron emission, electron excitation results from the con- version via Auger processes of the potential energy carried by the incoming ions when they are neu- tralized by electron capture from the surface. In ki- netic electron emission, excitation results from the transfer of kinetic energy of the incoming ion. These excitation mechanisms have been exten- sively studied using metal target, while insulator materials received considerable less attention, due to experimental difficulties arising because the sur- face charges up during ion bombardment. Among the insulator materials which are cur- rently the subject of an intense scrutiny, magne- sium oxide is one of the most interesting. This is 0168-583X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2004.12.083 * Corresponding author. Address: Laboratorio IIS, Diparti- mento di Fisica, Universita ´ della Calabria, and INFM Unita ` di Cosenza, 87036 Arcavacata di Rende, Cosenza, Italy. E-mail address: riccardi@fis.unical.it (P. Riccardi). Nuclear Instruments and Methods in Physics Research B 230 (2005) 455–459 www.elsevier.com/locate/nimb