Based on the Pauling's nature of chemical bond, the valence electron structures of diamond. Si and c-BN crystals have been constructed and the relative electron density difference (REDD) between the diamond (1 0 0) plane and 22 planes in Si and c-BN substrate, respectively, have been calculated. The experimental results, that the diamond (1 0 0) film can exclusively grow directly on the (1 0 0) oriented c-BN substrate, have been explained satisfactorily from minimization of the electron density difference across the interface. (c) 2006 Elsevier B.V. All rights reserved.