2X4 MISSING DIMER RECONSTRUCTION MODELS OF CUBIC BORON-NITRIDE (001)

Missing dimer models which conform to the electron-hole counting rule have been found energetically favourable for other 3-5 semiconductor m aterials. We perform molecular cluster calculations using the AM1 :Ham iltonian to study several of these models for the nitrogen-terminated c-BN(001) surface, and compare them with structures terminated with a full coverage of nitrogen dimers or N-N bridges. We find that the ener getics is dominated by elastic distortion effects related to the diffe rent atomic sizes of boron and nitrogen atoms, and the counting rule i s not a reliable guideline for c-BN. The most favourable models are th ose with a low nitrogen coverage and N-N bridges rather than dimers.