Energy and Angular Distributions of Secondary Ions Ejected from Clean Metals by MeV Ion Impact

Abstract

Positive and negative secondary ions desorbed from clean metal foils by bombardment with ²⁵²Cf fission fragments have been investigated by time of flight mass spectroscopy. The axial and radial velocity of each single ion has been measured using a position sensitive stop detector. By means of the correlated time- and position signal the energy-and angular distributions of the secondary ions were evaluated. The results obtained with metallic surfaces show essential differences compared to those with insulating materials. The energies of metal ions ejected from clean metal surfaces reach 1 keV; their mean energy is about 50 eV. Secondary ions from insulators on the other hand have energies of about 1–5 eV [4]. The energy distributions are in agreement with usual sputter theory for neutrals, the emission angle shows a simple cos(6) distribution.