Simulated hydrogen diffusion in diamond grain boundaries
To evaluate hydrogen diffusion within diamond, a series of molecular dynamics simulations have been carried out in which diffusion coefficients and activation energies were determined. Diamond grown via chemical vapour deposition (CVD) contains a high hydrogen concentration within grain boundaries, because of this, common tilt grain boundaries (111 Σ3, 112 Σ3, 114 Σ9 and 221 Σ9) were recreated from transmission electron microscopy images taken from literature. Diffusion coefficients of hydrogen placed within the grain boundary were estimated and compared to the bulk diffusion. Unlike many crystalline structures, some grain boundaries presented limited diffusion when compared to the bulk. This is thought to be a result of the formation of sp3C-H bonds with sp2 carbon present within the grain boundary and was explored by considering coordination numbers, as well as bond length and angle distributions. Potential wells were observed across some but not all the grain boundaries resulting in hydrogen trapping and anisotropic diffusion.