Re-emission of hydrogen implanted into graphite by helium ion bombardment

Helium ion-induced re-emission of hydrogen implanted in graphite with 5 keV H2+ ion beam at room temperature has been investigated in the energy range from 60 to 200 keV, by means of a high energy elastic recoil detection method with 16 MeV O5+ ion beam. The hydrogen concentrations in graphite rapidly decrease with increasing the He+ ion fluence and reach a constant value of H/C≅0.2. The re-emission rates of hydrogen from graphite increase with decreasing incident energy of the He+ ion. The He+ ion-induced detrapping cross-sections have been evaluated by analyzing the experimental data with mass balance equations including elementary processes such as detrapping, trapping and local molecular re-combination between an activated hydrogen atom and a trapped one. The elastic displacement collisions with energetic carbon recoils produced by He+ ion bombardments are dominant for the detrapping of hydrogen in the range of the incident energies.