石墨烯与金属的界面接触对电子输运影响的理论研究

Clear understanding of the origin of the graphene-metal contact resistance is central to the design of new graphene electronic device. In the present project, we propose to theoretically study the interfacial structure and the electron transport behavior in graphene-metal system using density functional theory and non-equilibrium green's function method. To reveal the origin of interfacial contact, we focus on the influences of key factors on electron transport in graphene-metal system, including electronic coupling of interface, spin polarization induced by magnetic metals, and defects in graphene(such as vacant defects, doping defects, and oxidation defects). From the results of binding energy, band structure, magnetic structure, density of states, transmission spectrum, and current-voltage curves, we can clarify the dependence of contact resistance on interfacial coupling and graphene structure. Then, by comparing non-magnetic metal with magnetic metal, the influence of magnetic metal on the contact resistance can be understood. Finally, we will point out the effects of various defects on geometric structure and transport behavior of graphene. To provide effective graphene-metal interfac, the metallic contact effects on electron transport through graphene are systematically investigated. The proposed research will be instructive to the design of graphene-based nanoelectronic devices.

对石墨烯/金属界面电阻起源的正确认识是实现其界面调控，成功设计新型石墨烯电子器件的基础。本项目利用密度泛函理论结合非平衡格林函数方法系统研究石墨烯与若干金属的界面结构特点和电子输运性质。将研究电子耦合强度、自旋极化、以及石墨烯缺陷(空穴、掺杂和氧化缺陷)对石墨烯/金属界面电子输运性质的影响。通过分析体系的结合能、能带结构、态密度、磁结构、透射谱及电流-电压关系等，阐明接触电阻对界面耦合、石墨烯构型的依赖性，揭示磁性金属和石墨烯缺陷导致的界面电子输运变化，以达到界面优化的目的，为石墨烯电子器件的设计提供物理依据。

本项目利用密度泛函理论结合非平衡格林函数方法系统研究了石墨烯与金属的界面结构特点和电子输运行为，主要从界面耦合强度、界面接触构型、金属磁性、石墨烯缺陷等几个方面阐明了金属对石墨烯的界面电子输运影响。(1)首先研究了界面电子耦合强度对石墨烯/金属电子输运性质的影响，发现弱相互作用的Cu/石墨烯的界面接触电阻约为强相互作用的Ni/石墨烯的10倍，分别从轨道杂化、电子通道数目、轨道对称性解释了不同金属对界面接触电阻的影响；(2)其次研究了界面接触构型对石墨烯电子输运性质的影响，发现随接触面积增加时，Cu/石墨烯纳米结的电导先增加后减弱，而Ni/石墨烯纳米结的电导单调增加。这是由于Cu/石墨烯中界面电荷转移占主导作用，而Ni/石墨烯中轨道杂化作用随接触面积的增加而增强，导致电导的显著提高；(3)进一步研究了磁性金属与石墨烯纳米带的界面自旋电子输运，发现Ni/扶手椅型石墨烯纳米带/Ni的自旋过滤效率可以达到98%，从理论上预测在非磁性的扶手椅型石墨烯纳米带与铁磁性金属构建的纳米结中可以实现半金属性质，而且Ni/扶手椅型石墨烯纳米带/Ni的纳米结具有一定的磁阻性质。本项目系统研究了金属接触效应对石墨烯电子输运的影响，获得了预期的研究成果，为实验上设计石墨烯电子器件提供理论依据。