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 wi th different primary beam conditions, and the positive secondary ions were mass- and energy-analysed by means of a Time-of-Flight Secondary Ion Mass S pectrometer, In the context of a wider study devoted to the emission proces ses 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 i ncidence angle) on the kinetic energy distributions (KED) of the observed i ons. In general, the shape of the measured kinetic energy distributions is almost independent on the primary ion energy, as shown by the similar spect ra observed with 7-22 keV In+ primaries. Nevertheless, the energy spectra o f the fingerprint fragment ions obtained at 2 keV with an impact angle of 6 5 degrees are broader than those observed for higher energy and lower impac t 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 siz e, up to 15% of the total ion intensity for C17H12O5+. The results are disc ussed in terms of collision cascade propagation in the surface region of th e target, by comparing the experimental observations to simulations realise d with the TRIM code. (C) 1999 Elsevier Science B.V. All rights reserved.