MEV ION SPUTTERING OF POLYMERS - CORRELATION BETWEEN SECONDARY-ION RADIAL-VELOCITY DISTRIBUTIONS AND HEAVY-ION TRACK STRUCTURE

Systematic investigations of the initial radial velocity distributions of low mass positive and negative secondary ions, sputtered electroni cally from thin films of polyvinylidene fluoride and polystyrene, are reported. 72.3 MeV I-127(13+) primary ions bombard the targets at 45-d egrees angle of incidence. Sputtered secondary ions in an individual M eV ion impact are analysed in a high resolution time-of-flight mass sp ectrometer. The accurate mass measurements of all ion peaks in the ran ge from 1 to 100 m/z provide unequivocal determination of the chemical composition of these ions, forming homologous series, C(n)H(m)+/- and C(n)H(m)F(p)+/-. Plots of both the initial mean radial velocity ([v(x )]) and kinetic energy (is-proportional-to (v(x)2)) as a function of t he ion m/z results in a periodic pattern. Ions with lower hydrogen con tent exhibit wider velocity distributions (i.e. higher [v(x)2]) and [v (x]) directed towards the primary ion trajectory. Ions with higher hyd rogen content have lower mean kinetic energies and [v(x)] directed awa y from the incident ion trajectory. We argue that the [v(x)] and [v(x) 2] periodic behaviour, connected to the chemical constitution of the i ons, reflects the radial profile of the deposited energy density in th e heavy ion track.