CALCULATION OF THE STRAIN-INDUCED SHIFTS IN THE INFRARED-ABSORPTION PEAKS OF CUBIC BORON-NITRIDE

The effects of strain on the zone-center TO phonon frequencies of cubic BN (and, hence, the positions of the infrared-absorption peaks) are calculated using an ab initio pseudopotential linear-combination-of-atomic-orbitals method. The calculated phonon wave number for the unstrained material is 1063 cm-1, in excellent agreement with the experimental value. The calculated line shift is -34 cm-1 per 1% isotropic strain, and for uniaxial strain, is -61 and 10 cm-1 per 1% strain for phonon polarizations parallel and perpendicular to the strain axis, respectively. The Poisson ratio of the material is calculated to be 0.316. These results are expected to be useful in the experimental characterization of homogeneous and inhomogeneous strain in cubic BN thin films using infrared spectroscopy. © 1995 The American Physical Society.