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，明确了Ni （ll）上六方氮化硼单层外延膜的金属性质。不匹配h-BN层在Pd和Pt （lll）上的界面成键较弱，而匹配h-BN层在Ni （lll）上的界面成键较强。与这些原子结构相关，声子色散的异常特征在相应层中被检测到：一是二维布里渊区伽玛点处LO和SH模式的简并。另一个是LA和TO分支交叉点的能隙（物理学报，1997,19,4609）。为了了解这些性质，我们用lcao - dv - x - alpha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轨道和Ni的d轨道之间发生了杂化。结果，在界面杂化带处产生了金属特征，这导致了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.