Kinetic energy distribution of molecular fragments sputtered from poly(ethylene terephthalate) under indium ion bombardment: effects of the primary beam energy and angle

Thin poly(ethylene terephthalate) (PET) films were bombarded by In+ ions with different primary beam conditions, and the positive secondary ions were mass- and energy-analysed by means of a Time-of-Flight Secondary Ion Mass Spectrometer, In the context of a wider study devoted to the emission processes of molecular ions sputtered from polymers, the aim of this work was to check the influence of two of these parameters (primary impact energy and incidence angle) on the kinetic energy distributions (KED) of the observed ions. In general, the shape of the measured kinetic energy distributions is almost independent on the primary ion energy, as shown by the similar spectra observed with 7-22 keV In+ primaries. Nevertheless, the energy spectra of the fingerprint fragment ions obtained at 2 keV with an impact angle of 65 degrees are broader than those observed for higher energy and lower impact angle (7-22 keV; similar to 40 degrees), Indeed, the KEDs measured in the (2 keV; 65 degrees) bombardment conditions show an additional contribution centred around 5-6 eV, i.e. in the high energy tail of the distributions. The relative intensity of this contribution increases with the fragment size, up to 15% of the total ion intensity for C17H12O5+. The results are discussed in terms of collision cascade propagation in the surface region of the target, by comparing the experimental observations to simulations realised with the TRIM code. (C) 1999 Elsevier Science B.V. All rights reserved.