The angular dependence of the charged fractions of H and He backscattered from Au

Abstract

To obtain more experimental information on the charged fractions of particles emerging from solids we have studied their angular dependence for H and He backscattered from a clean polycrystalline Au target, which was bombarded at normal incidence. Energy distributions of the scattered particles (neutrals and positive and negative ions) were measured as a function of the emergence angle. The charged fractions are determined as a function of the energy of the backscattered particles for scattering angles in the range of 95°–155°. There are striking differences for H and He. For H the charged fraction increases approximately linearly with the exit energy. At all exit energies it decreases with increasing exit angles measured from the surface normal, but is independent of the scattering angle. He shows sharp peaks in the charge fraction for particles scattered from the surface. The peak heights depend on the scattering angles. Charge fractions from below the surface do not show an angular dependence.