The depth profiles of H and D implanted at low energy (0.7 and 1.5keV) in highly oriented pyrolytic graphite (a-axis) and vitreous carbon, and then partially released by pulsed laser induced desorption were investigated in order to understand the H behaviour in carbon at high temperature. During the laser desorption experiment, the re-emitted gas quantity was measured as a function of laser energy density by mass spectrometry. Depth profiles of H and D remaining after partial desorption were also obtained by means of the elastic recoil detection E x B technique. Firstly, a significant difference between the re-emitted H2 or D2 gas quantity and the released amount deduced from the elastic recoil detection profiles was observed. This could be explained by atomic H release or by far in-depth diffusion of molecules. Secondly, it was seen from the depth profiles of hydrogen in highly oriented pyrolytic graphite that no profile modification was observed below 1500K. The desorption process was compatible with a local molecular recombination model with fast diffusion of the molecules. At higher temperatures, significant diffusion of atomic hydrogen permitted it to be re-trapped in the vacancy profile created during the implantation.

Detrapping and Diffusion of H and D Implanted in Carbon Studied by High Temperature Laser Annealing and Depth Profiling. Schiettekatte, F., Ross, G.G., Terreault, B.: Journal of Nuclear Materials, 1998, 256[1], 78-84