Trapping, detrapping and replacement of keV hydrogen implanted into graphite

Abstract

Trapping and detrapping of low energy hydrogen isotopes in graphite is relevant to the collection of fuel particles in graphite probes for diagnostics of particle fluxes and energies in the plasma boundary layer, and to the recycling of fuel particles. The measurement of saturation concentrations by depth profiling of D may be influenced by detrapping of deuterium by the analyzing ion-beam. Detrapping yields have been measured for 1 and 8 keV deuterium implanted to saturation concentrations in papyex and pyrolytic graphite at room temperature by 790 keV H +, 400–2500 keV 3He +, and 400–1600 keV 14N + ions. Initial detrapping yields of 1 keV implanted deuterium by 790 keV 3He + and 14N + are 4 and 56 D-atoms/ion, respectively. The detrapping yiled for 14N +-ions increases with increasing energy similar to the electronic stopping power of the ions indicating the influence of electronic excitation on the detrapping mechanism. Detrapping by 790 keV H + was found to be negligible. Papyex and pyrolytic graphite show similar behavior. Careful determination of the deuterium saturation concentration from the D concentration profile by D( 3He, α)H nuclear reaction method and taking detrapping into account yields a value of 0.4 D-atoms/C-atom. Furthermore, the replacement of hydrogen by deuterium at equal ranges (8keV H +, 7keV D +) has been measured in pyrolytic graphite with elastic recoil detection (ERD) by 2.6–2.8 MeV 4He ions. The H/D isotopic replacement behavior in saturated layers is similar to that found in metals at low temperatures and in low- Z coatings as TiC at room temperature.