Multiply charged direct recoil spectra from Ar+ and Kr+ bombarded graphite

Measurements of the energy spectra of multiply charged positive and negative carbon ions (C-n+/-) recoiling from graphite surface under 100 and 150 keV argon and krypton ion bombardment are presented. With the energy spectrometer set at recoil angle of 79.5 degrees, direct recoil (DR) peaks have been observed with singly as well as multiply charged carbon ions C-n+/-, where n = 1 to 6. These C-n+/- ions have been seen recoiling with the characteristic recoil energy E(DR) = kE(0)cos(2) theta(DR), where theta(DR) is the direct recoil angle, k = 4m(1)m(2)/(m(1)+m(2))(2), m(1) and E(0) are projectile mass and energy and m(2) is carbon mass. We have observed sharp DR peaks. A collimated projectile beam with divergence similar to +/-0.2 degrees is supplemented with a similar collimation before the energy analyzer to reduce the background of sputtered ions due to scattered projectiles.