Sputtering of metals: Probing and modelling the emission of atoms in different electronic states

This paper deals with the investigation of electronic processes involved in the emission of neutral atoms during keV ion-beam sputtering of metals, We first present an experimental study of Ar+ ion-beam sputtering of clean, p olycrystalline metals. Atoms emitted in the ground and metastable states ar e probed using double-resonant laser ionization. These efficient probing sc hemes allow the quantitative determination of population partitions as well as state-specific, kinetic-energy (KE) distributions. Experimental data on the sputtering of Co, Ni, Cu, Sr and Ag are reported. In the second part o f this article it is shown that the en-.Lission of neutral atoms during spu ttering of metals can be modelled as follows: as a result of the collision cascade created by the incoming particles, a sputtered particle escapes fro m the surface as a positive ion and becomes neutralized by resonant transfe r of an electron from the valence band of the metal. A qualitative descript ion of this multichannel electron transfer process is given, explaining the main observations of these sputtering studies. (C) 2001 Elsevier Science B .V. All rights reserved.