Enhancement of Surface Hardness: Boron on Diamond (111)

Abstract

We have performed {ital ab initio} pseudopotential calculations for the diamond (111) surface with nitrogen or boron replacing the surface carbon atoms. Surface boron atoms form planar sp{sup 2} bonds with carbon atoms and the compressive stress from the underlying bulk diamond lattice squeezes the B-C bonds significantly. Bulk and shear moduli in the surface region increase substantially, surpassing those of bulk diamond. In contrast, for the nitrogen-covered surface, N-C bonds are elongated because of the tensile stress from bulk diamond and the elastic stiffness decreases. {copyright} {ital 1998} {ital The American Physical Society}