Hydrogen diffusion and stability in polycrystalline CVD undoped diamond

Abstract Diffusion profiles and effusion experiments performed on post-hydrogenated (deuterated) CVD diamond layers (grain size 2 and 0.2 μm) are reported in order to study the configurations and stability of hydrogen bonding in polycrystalline undoped CVD diamond. Deuterium is used as a tracer to improve the hydrogen detection limit. The diamond layers are first annealed at 1200°C in order to out-diffuse hydrogen present in the as-grown sample. Then the samples are exposed either to a radiofrequency plasma or a microwave plasma and the deuterium diffusion profiles are analyzed by secondary ion mass spectrometry. For r.f. and microwave plasma, the diffusion profiles are explained in term of trapping on plasma-induced defects near the surface and/or on inter- and intra-granular defects. The mean free paths of deuterium and capture radius of traps are calculated by fitting the deuterium diffusion profiles and depend on the grain sizes. Some CVD diamond layers are deposited using a gas mixture (CH 4 +D 2 ) and a deuterium concentration of 3×10 19 cm −3 , originating from the vector gas, is found in these as-grown samples. The stabilities of deuterium bonding in as-grown and post-deuterated samples are compared.