Adsorption of H, NH_x, BH_x and BBr_x on a (110) surface of c-BN: A quantum-mechanical DFT study

摘要

The adsorption of H, NH_x, BH_x and BBr_x (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 approx = BBr_2>NH_2_》BH_3>NH_3>BBr_3 for a nitrogen site, and NH_2>NH>BBr>H>BH>BH_2 approx = BBr_2 》BBr_3 approx = NH_3 approx BH_3 for a boron site. The exception was NH_3 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.