节点文献
氮化硼—石墨烯复合纳米体系的电子结构与输运性质研究
Electronic and Transport Properties of Boron Nitride-Graphene Hybrid Nanostructures
【作者】 肖化平；
【导师】 钟建新；
【作者基本信息】 湘潭大学 ， 凝聚态物理， 2012， 博士
【摘要】 随着石墨烯、石墨烯纳米带、碳纳米管、单原子层六角氮化硼薄膜、六角氮化硼纳米带、六角氮化硼纳米管的成功制备，这些低维纳米材料在微纳电子器件领域展现出巨大的潜在应用前景，基于碳（C）及氮化硼（BN）的纳米材料很快成为凝聚态物理的研究热点，随着研究的深入，基于BNC的复合纳米结构由于具有独特的结构、丰富的物理化学性质、自旋极化特性及其电子结构和输运性质的可控调制特征，也很快引起了人们的关注。本文针对几种典型的BNC复合纳米材料的结构特征、电子结构及其输运性质进行了系统的研究，得到了如下主要研究成果：1.基于密度泛函理论的第一性原理方法，研究了尺寸效应对锯齿型BNC复合纳米带中半金属特性的制约机制。结果表明，所有的两片段BNC复合纳米带都具有反铁磁的基态，当纳米带中的固定ZGNR片段包含9条锯齿型碳链时，其电子性质基本上不受ZBNNR片段宽度变化的影响。对于具有固定的9条锯齿型BN链的纳米带，其电子结构随着ZGNR片段的增加而出现从半导体-半金属-金属的转变，转变尺寸依赖于复合界面的类型。2.基于密度泛函理论和非平衡格林函数方法，系统研究了两片段的复合纳米管BN20-nCnNTs以及四片段复合纳米管BNmCmBNmCmNTs和BNmCmNBmCmNTs （m=3,4,5）的结构稳定性、电子结构及电子输运性质特征。结果表明，两片段复合纳米管BN20-nCnNTs属于带隙依赖于组分的窄带隙半导体；所有四片段的BNmCmBNmCmNTs都属于半导体，带隙随着直径的增长而下降，而所有四片段的BNmCmNBmCmNTs都属于金属。进一步的传输性质研究表明，两片段的复合管型并不能带来电子输运上的增益，而四片段的复合管型则在费米能级附近带来很好的增益。金属型的BN5C5NB5C5NT比半导体型的BN5C5BN5C5NT增益更明显，在其费米能级出现高达6G0的传输平台。3.基于密度泛函理论和非平衡格林函数方法，系统研究了由单壁碳纳米管和单壁氮化硼纳米管构成的异质结构（BN/C）中的电子输运性质和可调制微分电阻效应。以（5,5）型碳纳米管和氮化硼纳米管为基础构建模型，结果表明，BN/C纳米管异质结的传输电导和微分电导将随着氮化硼管比例的增加而逐渐下降。4.基于密度泛函理论和非平衡格林函数方法，研究了将石墨烯纳米带中碳原子链替换为B（N）原子链构成的复合石墨烯纳米带中的电子输运性质。结果显示扶手型的复合纳米带从半导体转变为金属，而锯齿型的复合纳米带的电子输运性质得到了极大的提高，其费米能附近的电子传输电导增加到6G0（5G0）。5.基于安德森紧束缚模型，研究了无序双层六角氮化硼量子薄膜的电子性质。数值计算结果表明在双层都无序掺杂的情况下，六角氮化硼量子薄膜的电子是局域的，其表现为绝缘体性质；而对于单层掺杂（无论是氮原子还是硼原子）的双层六角氮化硼量子薄膜，在能谱的带尾出现了持续的迁移率边，这说明在单层掺杂的双层六角氮化硼量子薄膜中产生了金属绝缘体转变。
【Abstract】 With the successful preparation of advanced nanomaterials of carbon （C） andboron nitride （BN）, such as graphene, graphene nanoribbons （GNRs）, h-BN-sheets,boron nitride nanoibbons （BNNRs）, carbon nanotubes （CNTs） and boron nitridenanotubes （BNNTs）, and their potential applications in future nano-electronics, theseC-or BN-based nanomaterials become the research focus in condensed matter physics.The boron nitride-graphene hybrid nanostructures with unique structure, rich physicaland chemical properties, spin polarization properties and modulated electronic andtransport properties soon arouse people’s attention. In this thesis the structuralcharacteristics, electronic structures and transport properties of several typical boronnitride-graphene hybrid nanomaterials are systematically investigated. Somesignificant results are summarized as follows:1. We report the size limitation effct of the half-metallic properties in the hybridzigzag BNC nanoribbons using the density functional theory based first-principlesmethods. We find that all hybrid systems hold antiferromagnetic ground states.Systems holding ZGNR segments with fixed9zigzag carbon chains are metals notdepending on the variation of the ZBNNR segments. Transitions betweensemiconductor, half-metal and metal can be realized in both systems as the width ofthe carbon segment increases.2. The structures, stability and electronic properties of a series two-segmenthybrid nanotubes BN20-nCnNTs and some novel four-segment hybrid nanotubesBNmCmBNmCmNTs and BNmCmNBmCmNTs （m=3,4,5） are systematically investigatedusing the density functional theory in combination with non-equilibrium Green’sfunctions. We find that the two-segment nanotubes can be narrow band-gapsemiconductors depending on their chemical compositions. All four-segmentBNmCmNBmCmNTs are metals and all four-segment BNmCmBNmCmNTs aresemiconductors with band gaps decreasing as the increasing of their diameters.Further investigations on the transport properties of the pure C20NT, the two-segmentBN10C10NT and the four-segment BN5C5BN5C5NTs and BN5C5NB5C5NTs reveal thatthe two-segment hybrid manner could not improve the tube’s transport properties.However, an obvious transport enhancement is found in the four-segment nanotubes,especially in the metallic BN5C5NB5C5NTs where a6G0transmission peak appears inits transport spectrum.3. The transport properties and differential conductance of the heterostructuresconstructed by single-wall carbon nanotube （SWCNT） and single-wall boron nitridenanotube （SWBNNT） are investigated using the density functional theory incombination with non-equilibrium Green’s functions. SWCNT（5,5） and SWBNNT （5,5） are taken as example. We find that the transmission conductance and differentialconductance of （5,5） BN/C nanotube heterostructure are continually depressed as theBNNT region increases.4. The electronic transport properties of hybrid graphene nanoribbons constructed by substituting C atom chain into B （N） atom chain are investigated using the densityfunctional theory in combination with the non-equilibrium Green’s functions. It isfound that the hybrid nanoribbon with armchair edge transits from semiconducting tometallic. While the transport properties of hybrid B （N） system with zigzag edge arehighly improved with the transmission conductance around the Fermi level increasingto6G0（5G0）.5. Based on the Anderson tight-binding model, the electronic properties ofdisordered bilayer hexagonal boron nitride quantum films are investigated. Ournumerical results show that the electrons in disordered bilayer hexagonal boronnitride quantum film are localized, presenting an insulating behavior. However, forthe monolayer disordered bilayer hexagonal boron nitride quantum film, the energyspectrum has persistent mobility edges which are independent of the disorder strength.This indicates that a metal-insulator transition occurs in the monolayer disorderstructure.