A model of hydrogen implantation into graphite including bulk recombination by tunneling

Abstract

A distinctly new model for bulk hydrogen recombination in hydrogen implanted graphite is presented. The model considers deep H-atom traps (2.8 eV), but the thermal properties of the recombination and release are determined by shallow (few tenths eV) localized vibrational modes within the trapping potential well in combination with tunneling between trap sites. Four sources of hydrogen recombination are considered: i) direct recombination of hydrogen implanted into a hydrogen rich region, ii) recombination of hydrogen displaced from traps by the incident beam, iii) recombination of hydrogen which tunnels through the potential barrier separating adjacent trap sites, and iv) diffusive recombination. A mechanism for thermal relaxation of the localized vibrational modes is included in the model. Interaction of the incident beam with both trapped atomic H and diffusing molecular H 2 is considered in the model. Various implantation parameters and interaction cross sections required by the model are evaluated with TRIMRC calculations. Other parameters are obtained from the literature or from fits to experimental data. The model is found to give good agreement with experimental inventory versus isochronal anneal temperature, saturation inventory versus implantation temperature, and ion-induced release versus ion fluence measurements. Experiments for confirming the model are suggested.