Hydrogen and Halogen Bonding on The Diamond (100)2 × 1 Surface: An Ab Initio Study

ABSTRACTThis work addresses mechanistic issues in conventional and halogen-assisted diamond growth via ab initio molecular orbital calculations on hydrogenated and halogenated carbon clusters (C9H12Xi, X=H, F, or Cl; i=O, 1, or 2) as models of the dimer-reconstructed diamond (100)2× 1 surface. The dimer bond lengths (XC-CX, XC-C., C=C) and the C-X and C=C π bond energies have been determined along with the effects of lattice constraints. The calculations show that dimer bonds are longer in clusters where only the topmost carbon layer is allowed to relax and the remaining carbon atoms are constrained to lie at diamond lattice positions than in fully relaxed clusters. The calculations also predict that the first C-X bond strength is approximately the same in constrained and fully relaxed clusters and that the second C-X bond is distinctly weaker due to π bond formation, particularly in fully relaxed clusters. These results indicate that the π bond between dimer atoms on the clean (100)-(2× 1) surface is weakened considerably by the constraints imposed by the lattice but is quite important nonetheless.