EVIDENCE FOR A SINGLE SHALLOW HYDROGEN TRAP IN HYDROGEN IMPLANTED GRAPHITE

Experimental ion-induced hydrogen release cross sections from W.R. Wampler and B.L. Doyle for 3000 eV C+, 1200 eV He+, and 600 eV He+ projectiles incident on graphite saturated by 300 eV D+ implantation are compared with cross sections calculated using the computer code TRIMRC. The comparison suggests that trap binding energies for hydrogen in the implanted region of graphite are significantly less than the currently accepted values of 2.3 eV to 4.3 eV. Data from the literature for isochronal anneal measurements versus temperature for implanted D, H and T release, and experimental D and H saturation concentrations as a function of implantation temperature are examined using a model with a single hydrogen trap energy and a recombination barrier to hydrogen release. All experimental data are found to be accurately described by the model. For recombination coefficient, K = K0T- 1 2exp(-EK/kBT) the isochronal anneal data yield a trap energy Eb ∼ 0.1 eV, and EK ∼ 0.7 eV with K0 ∼ 0.38-1.2 × 10-24cm4(K) 1 2/s. The saturation at implantation temperature data yield Eb ∼ 0.3 eV, Ek ∼ 0.35 eV, with K0 in the same range as for the isochronal anneal analysis. Additional calculations and experiments are suggested. © 1990.