Studies on Electronic and Phonon Structures of Epitaxial h-Born Nitride Films

根据电子能带结构、声子色散和原子结构的实验数据，结合理论计算，阐明了六方氮化硼在Ni（Ⅲ）表面单层外延膜的金属性。在Pd和Pt（III）上的非公度h-BN层的界面结合较弱，而在Ni（III）上的公度h-BN层的界面结合较强。与这些原子结构相关的声子色散的反常特征在公度层中被探测到：一是在二维布里渊区的Gamma点处LO模和SH模的简并。另一个是LA和TO分支交叉点处的能隙（Phys.Rev.Lett.79，1997，4609），为了理解这些性质，我们用LCAO-DV-Xalpha方法计算了单层h-BN薄膜的电子能带结构。能带结构和局域态密度随界面间距的变化表明，B和N的Pz轨道与Ni的d轨道之间存在杂化。结果，在界面杂化带处产生金属特征，这导致观察到的两个声子的简并。

On the basis of the experimental data of electronic band structure, phonon dispersion and atomic structure together with the theoretical calculations, we have clarified metallic characters of a monolayr epitaxial film of hexagonal boron nitride on Ni (lll). The interfacial bonding is week on the imcommensurate h-BN layr on Pd and Pt (lll), while the relative strong bonding occurs for the commensurate h-BN layr on Ni (lll). As related to these atomic structures, anomalous features of phonon dispersion have been detected for the commensurate layr : One is the degeneracy of LO and SH modes at the GAMMA point of two dimensional Brillouin zone. Another one is the energy gap at the cross point of the LA and TO branches (Phys.Rev.Lett.79,1997,4609).In order to understand the those properties, we have calculated the electronic band structure of a monolayr h-BN films by means of LCAO-DV-Xalpha method. The band structures and the local density of states as a function of the interfacial spacing have shown that the hybridization occurs between Pz orbital of B and N and d orbital of Ni. As a result, the metallic character is generated at the interfacial hybridized bands, which results in the observed degeneracy of two phonons.