Inferring ejection distances and a surface energy pro®le in keV particle bombardment experiments A. Delcorte a, * , B.G. Segda b,1 , B.J. Garrison a , P. Bertrand b a Department of Chemistry, Penn State University, 152 Davey Lab, University Park, PA 16802-6300, USA b Unit e de Physico-Chimie et de Physique des Mat eriaux, Universit e Catholique de Louvain, 1 pl. Croix du Sud, B-1348 Louvain-la-Neuve, Belgium Received 23 March 2000; received in revised form 2 May 2000 Abstract The disappearance cross-sections and kinetic energy distributions of fragment ions sputtered from polystyrene thin ®lms under 12 keV 69 Ga  ion bombardment are measured using a time-of-¯ight spectrometer. Even though the dis- appearance cross-sections are often used as an indicator of radial ion beam damage, the derived radii range from 2 to 10  A depending on the particular hydrocarbon fragment. Therefore, the disappearance cross-sections cannot be directly related to a single global quantity of damage per incident particle. Likewise, the widths of the measured kinetic energy depend on the particular hydrocarbon fragment. Both the disappearance cross-sections and the widths of the kinetic energy distribution super®cially relate to fragment mass but the correlation is not perfect. We develop a hypothesis that the disappearance cross-section and the width of the kinetic energy distribution actually correlate with the ejection radius of the particular fragment. Thus, the kinetic energy distributions provide an estimate of the radial extent of the energy density in the ejection region. Our interpretations are supported by molecular dynamics simulation results. For comparison with previously reported data, our results indicate that the deposited energy pro®le is 4±5 times narrower than for 72.3 MeV, electronic sputtering of PVDF [Phys. Rev. Lett. 77 (1996) 667]. Ó 2000 Elsevier Science B.V. All rights reserved. Keywords: Secondary ion mass spectrometry; Sputtering; Ion emission; Kinetic energy distribution; Ion induced damage; Disappearance cross-section; Polymer; MD simulation 1. Introduction When an energetic primary ion interacts with an organic surface, atoms, small hydrocarbon fragments and characteristic molecular segments are sputtered in a neutral or charged state [2,3]. The mass-separation of the charged sputtered species constitutes the basis of secondary ion mass Nuclear Instruments and Methods in Physics Research B 171 (2000) 277±290 www.elsevier.nl/locate/nimb * Corresponding author. Tel.: +1-814-863-2108; fax: +1-814- 863-5319. E-mail address: delcorte@chem.psu.edu (A. Delcorte). 1 Permanent address: D epartement de Physique, Facult e des Sciences et Techniques, Universit e de Ouagadougou, BP 7021 Ouagadougou 03, Burkina Faso. 0168-583X/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 0 ) 0 0 2 6 3 - 9