Deuterium retention in CVD diamond: Combined experimental and computational study

Abstract

Diamond’s intrinsic hardness, excellent thermal conductivity and low atomic number make it a highly promising candidate as a plasma facing material. However, as with the previously used graphite, concerns over tritium retention and resultant chemical etching have so far limited research interest in the use of synthetic diamond. In order to study tritium retention, the DELPHI facility at the Culham Centre for Fusion Energy was used to expose polycrystalline diamond samples to a deuterium plasma. Deuterium ions were accelerated to an energy of 0.2 keV to 1 keV for a 5 h exposure time, achieving a fluence of approximately 5.5 × 1021 D m−2. Exposed samples were analysed using Thermal Desorption Spectroscopy. Increasing implantation energy resulted in additional D2 release peaks observed in the 800–1100 K temperature range that were not seen at lower energies. These peaks were interpreted as an additional bonding mechanism, a likely candidate for which is inter-grain deuterium. Experimental work was complemented with molecular dynamics simulations on the University of Bristol’s high performance computer—Blue Crystal Phase 4. In these simulations, both varying implantation energy and the presence of grain boundaries were explored. A two-step etching mechanism was observed, in which the surface initially swelled before carbon removal. No significant differences could be observed on the inclusion of a grain boundary at the energies tested.