ISOTOPIC EFFECT IN ION-INDUCED REEMISSION OF HYDROGEN IMPLANTED INTO GRAPHITE

The re-emission of H and D atoms, implanted into graphite, induced by 1.5 MeV He+ bombardment has been studied by means of the elastic recoil detection (ERD) technique by changing the initial peak concentration of H and D, the temperature and the He+ ion flux. The experimental re-emission profiles were analyzed solving analytically the mass balance equations. The whole re-emission profiles are shown to be excellently reproduced in terms of the ion-induced detrapping (sigma(d)), trapping (or retrapping) (SIGMA(T)) and local molecular recombination (K) between an activated (free) hydrogen atom and a trapped one and that the effective detrapping cross sections sigma(d)K/SIGMA(T) for H and D are determined as the best fitting parameter to be 2.9 x 10(-18) and 7.7 x 10(-19) cm2, respectively. It is also shown from the experimental data on little dependence of the re-emission profile on the He+ ion flux that the local molecular recombination plays a major role in the ion-induced re-emission. Furthermore, the difference between the effective detrapping cross sections for H and D is reasonably explained in terms of isotopic difference in the values of K for H and D.