Ab initio study on surface segregation of hydrogen from diamond C(100) surfaces

The segregation of a hydrogen (H) atom to the monohydride diamond C(100)2 × 1 surface from the subsurface, which consists of two elementary processes of lateral migration in the subsurface and migration to the surface from the bulk, has been investigated by ab initio pseudopotential method. Since the activation energy barrier (AEB) for H migration in the subsurface perpendicular to dimer rows markedly decreases due to the presence of an H defect on the surface, it becomes an easy diffusion path and the diffusing H atoms tend to approach a position under a hollow site. The AEB for H migration to the surface from the bulk also markedly decreases due to the H defect on the surface. Thus, the H defect on the monohydride surface is easily repaired by H atoms from the subsurface, resulting in the suppression of methane adsorption and diamond epitaxial growth. The theoretical results support the experimental observations.