ORIENTATION-DEPENDENCE OF ELASTIC STRAIN-ENERGY IN HEXAGONAL AND CUBIC BORON-NITRIDE LAYERS IN ENERGETICALLY DEPOSITED BN FILMS

Using anisotropic elasticity theory, we analyze the relative thermodyn amic stabilities of strained graphitic (hexagonal) BN and cubic BN (cB N) single-crystal structures for all orientations ofbiaxial stress and strain fields relative to the crystallographic directions. In hBN, th e most thermodynamically stable orientation has the graphitic basal pl anes oriented roughly 45 degrees relative to either the plane of stres s or strain. For cBN, the lowest-energy configuration differs for the constant stress or constant strain assumptions. Importantly, these mos t-stable orientations of hBN and cBN differ from those found experimen tally for graphitic BN and cBN in polycrystalline BN films produced by energetic deposition processes. Therefore, the observed textures are not those that minimize elastic strain energy. We discuss possible ori gins other than elastic strain-energy effects for the observed texture s. (C) 1997 American Vacuum Society.