Boron Incorporation at a Diamond Surface: A QM/MM Study of Insertion and Migration Pathways during Chemical Vapor Deposition

Quantum mechanical and hybrid quantum mechanical/molecular mechanical (QM/MM) cluster models have been used to investigate the energetics of (i) B atom and BH radical insertion reactions into surface C-H and C-C bonds during chemical vapor deposition (CVD) of B-doped diamond and (ii) BH group migration on the C{100}:H 2 X 1 and C{111}:H surfaces and at step edges between these surfaces. B and BH insertions into surface C-H bonds are shown to be energetically feasible routes to forming surface-bound BHx species under typical CVD conditions but are likely to be of minor importance compared with the alternative process, wherein a gas-phase BHx species adds to a surface radical site. BH migration on and between the C{100}:H 2 X 1 and C{111}:H surfaces involves passage through ring-closed intermediate structures. These are generally more stable than those involved in analogous CH2 migration reactions, with the result that BH groups are likely to be less migratory and to incorporate nearer the point where they initially accommodate on the diamond surface - most particularly at concave step-edges.