Substitutional boron and nitrogen pairs in diamond. A quantum mechanical vibrational analysis

Abstract

The lattice structures, electronic characteristics and spectroscopic features of the three vicinal substitutional, spin zero defects, Ns-Ns (A-centre), Bs-Bs, and Bs-Ns in diamond are reported. They are derived from all-electron B3LYP calculations based on Gaussian basis sets, within a periodic supercell scheme, including both 64- and 216-atom cells. The local geometry reflects the differences between the strong C-C bond of the host lattice and the weaker impurity-impurity bonding in the defective systems. The band structures show two occupied bands 1.06 eV above the VBE for Ns-Ns, and empty bands 3.36 eV and 0.25 eV below the CBE for Bs-Bs and for Bs-Ns respectively. The IR spectra of Bs-Bs and Ns-Ns contain sharp peaks at 631 cm−1, 692 cm−1 and 1373 cm−1, and 451 cm−1, 571 cm−1 and 1276 cm−1, respectively, which might reasonably be considered as ‘finger prints’ for these systems. For Bs-Ns, a set of medium intensity absorptions are predicted at 890 cm−1, 945 cm−1, 1018 cm−1, 1078 cm−1 and 1281 cm−1. However, numerous peaks in this region have been predicted for other defective systems, so that the firm identification of Bs-Ns based on these frequencies is much less certain than Bs-Bs and Ns-Ns.