Effect of radiation damage on ion-induced electron emission from highly oriented pyrolytic graphite

The dependences of ion-electron emission yields γ for highly oriented pyrolytic graphite (HOPG) under 30 keV N2+ ion irradiation on target temperature at different ion incidence angles (0-80°) have been measured. The fluences were 1018-1019 ion/cm2 and irradiation temperatures were varied from room temperature to 400 °C. At normal ion incidence a step-like increase of yield, analogous to the γ-behaviour for polygranular graphites, has been found at an annealing temperature Ta. This effect and the changes of γ(T) with ion incidence angle are discussed in terms of the change of electron path length and the transparency of the lattice for ion beams with increasing degree of lattice order.