RADIAL-VELOCITY DISTRIBUTIONS OF SECONDARY IONS EJECTED FROM PTFE BY MEV ATOMIC IONS

In this paper, systematic investigations of the initial radial velocit y distributions of CnFm+ secondary ions sputtered by 72.3 MeV I-127(+1 3) ions from polytetrafluoroethylene (PTFE) foils are presented. The i nitial radial velocity distributions are obtained by monitoring the se condary ion yield as a function of the voltages applied to two sets of deflection plates installed parallel to the ion optical axis of a tim e-of-flight mass spectrometer. The mean radial velocity, [v(x)], of Cn Fm+ ions (1 < n < 6 and 0 < m < 13) depends on the number of fluorine atoms, showing a periodic behaviour when plotted as a function of the ion mass. Ions with low fluorine content have [v(x)] directed towards the primary ion's line-of-incidence (positive mean velocities). Ions w ith a large number of fluorine atoms an ejected in an off-normal direc tion away from the incoming MeV ion trajectory (negative mean velociti es), The ion emission can not be explained only by evaporative type pr ocesses, Mechanisms involving correlated momentum transfer e.g. pressu re pulse or shock wave induced ejection, should also be taken into acc ount. The data obtained for fluorocarbon ions from a purely fluorinate d compound generalise a similar effect observed previously for CnHm+ i ons, sputtered from different hydrogen containing polymer targets [R.M . Papaleo et al., Nucl. Instr. and Meth. B 91 (1994) 667].