Sputtering with polyatomic ions: revisiting kinetic energy distributions of secondary ions I.V. Veryovkin a, * , S.F. Belykh b , A. Adriaens c , F. Adams b a Materials Science Division, Argonne National Laboratory, Bldg 200, 9700 S. Cass Ave, Argonne, IL 60439, USA b Department of Chemistry, University of Antwerp (UIA), B-2610 Antwerp Wilrijk, Belgium c Department of Analytical Chemistry, Ghent University, B-9000, Belgium Abstract A new more accurate data processing procedure for calibration of kinetic energies of secondary ions measured in magnetic sector secondary ion mass spectrometers has been developed. The procedure was applied to reprocessing of raw data from previously published measurements of kinetic energy spectra of secondary atomic and cluster ions sputtered from Ta by 6 keV/atom Au  ,Au  2 and Au  3 projectiles. Absolute energies of the sputtered Ta þ n ions were determined more accurately, which permitted a fairer comparison of energy spectra for the same secondary ions measured under bombardment with different primary ions. Most probable and mean energies were determined for the sputtered ions, and their energy spectra were converted into distributions over inverse velocities. The reprocessed experimentalresultsrevealedstrongdifferencesbetweenresultsforatomicanddiatomicionsandthoseforlargercluster ions (consisting of more than seven atoms). In particular, the comparison of atomic and polyatomic bombardment showed that there are strong differences between atomic and diatomic sputtered species, while there were almost no changes between larger sputtered clusters. Results are discussed in terms of observed enhancements under polyatomic ion bombardment for the total sputtering efficiency and the ionization of sputtered species. Ó 2004 Elsevier B.V. All rights reserved. PACS: 79.20.Rf; 34.50.Dy; 79.20.Rf; 68.49.Sf; 82.80.Ms Keywords: Sputtering by atom, molecule, and ion impact;Ion-surfaceimpact;Molecularbeamsinteractionswithsolids;Secondary-ion mass spectrometry (SIMS) 1. Introduction During the last decade, analytical applications of sputtering with polyatomic ions generated increasing interest in the ion-beam community, especiallythatpart,whichisengagedinsecondary ion mass spectrometry (SIMS) [1]. On the other hand, despite the fact that this ion bombardment regime has been long known to enhance yields of secondary ions [2], the mechanism of the enhancement remains poorly understood. It is presently unclear what actually increases under polyatomic ion bombardment: the total sputtering yield or the ionization probability of sputtered neutrals [3]. Moreover, for sputtered atomic and clusterions,theemissionenhancementobservedin experimentsmightbeduetodifferentreasons,such * Corresponding author. Tel.: +1-630-252-4657; fax: +1-630- 252-9555. E-mail address: verigo@anl.gov (I.V. Veryovkin). 0168-583X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2004.01.056 Nuclear Instruments and Methods in Physics Research B 219–220 (2004) 215–220 www.elsevier.com/locate/nimb