Adsorption of H, NHx, BHx and BBrx on a (110) surface of c-BN: A quantum-mechanical DFT study

The adsorption of H, NHx, BHx and BBrx (x = 1, 2 and 3) on hydrogen-terminated (110) surfaces of c-BN has been investigated theoretically. Density Functional Theory (DFT) methods were used in order to study the adsorption processes of these different species on both nitrogen and boron sites at the surfaces. With one exception, all adsorption processes were found to be exothermic and in the order; BBr· ≫ BH2· ≈H· > BH· ≫ NH· ≈ BBr2· > NH2· ≫ BH3· > NH3· > BBr3· for a nitrogen site, and NH2· > NH· > BBr· > H· > BH· > BH2· ≈ BBr2· ≫ BBr3· ≈ NH3· ≈BH3· for a boron site. The exception was NH3 being bonded to a surface N site, for which the reaction was slightly endothermic. The various modeling parameters that were used in the calculations of these adsorption energies have been chosen by performing series of extensive test calculations, in which the effect of these parameters (e.g. template size, vacuum depth, atom constraints) on bond-strength have been carefully estimated. Moreover, a semi-empirical method has been evaluated with the purpose to study the usefulness of this type of method for the polar BN compound.