ENHANCEMENT OF SURFACE HARDNESS - BORON ON DIAMOND(111)

We have performed ab initio pseudopotential calculations for the diamo nd (111) surface with nitrogen or boron replacing the surface carbon a toms. Surface boron atoms form planar sp(2) bonds with carbon atoms an d the compressive stress from the underlying bulk diamond lattice sque ezes the B-C bonds significantly. Bulk and shear moduli in the surface region increase substantially, surpassing those of bulk diamond. In c ontrast, for the nitrogen-covered surface, N-C bonds are elongated bec ause of the tensile stress from bulk diamond and the elastic stiffness decreases. [S0031-9007(97)05216-2].