Temperature dependence of ion-induced detrapping of deuterium in graphite

Abstract

We have extended our previous work on the release of deuterium from saturated near-surface layers of graphite by keV proton bombardment [B.M.U. Scherzer et al., Nucl. Instr. and Meth., to be published] t^ the temperature range 93 K ≤ T ≤ 573 K. The saturated deuterium layers were produced by 300 eV D + implantation. Retention and reemission of D has been measured for proton fluences up to 3 × 10 18 cm −2. The results suggest two different mechanisms to contribute to the release, one being due to detrapping of bound D by protons penetrating the deuterium layer, the other being due to deposition of protons in the deuterium layer up to saturation. The importance of the second mechanism compared to the first one increases with decreasing temperature. The results have been compared to model calculations taking into account detrapping by nuclear collisions, local retrapping and molecular recombination. This simple model is not suitable to describe the detailed release behaviour probably due to the presence of different types of traps and possibly to an inhomogeneity of structure with depth in the implanted films.