Simulated bombardment of diamond grain boundaries with deuterium
Diamond has several possible applications within fusion reactors, including windows, sensors/diagnostics and has shown promise as a plasma facing material. For some of these applications, polycrystalline diamond may be preferable to single crystal, meaning the impact of grain boundaries on retention mechanisms needs to be understood. As such, this work presents molecular dynamics simulations of deuterium bombardment normal to the (110) surface of four grain boundaries common to diamond grown via chemical vapour deposition. Repeated single bombardments of pristine structures showed channelling effects for some grain boundaries, that resulted in very high penetration depths. Furthermore, the additional space present in the grain boundaries allowed vacancies to form along the grain boundary at depths comparable to the deuterium depth - in contrast to bulk regions for which vacancy formation was limited to the surface. For continuous bombardment simulations, the formation of a disordered layer prevented channelling effects from playing a significant role, particularly for higher energies. A small increase in retention was observed in grain boundaries which was thought to be a result of the additional space within the grain boundary. Results presented here suggest changes in retention would be small for polycrystalline diamond of reasonable grain size.