Computational Materials Science Unit, National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan.
J Chem Phys. 2013 Aug 21;139(7):074703. doi: 10.1063/1.4818519.
We perform first-principles investigations of electron transport in armchair graphene nanoribbons adsorbed on Cu(111) and Ni(111) surfaces with various contact areas. We find that the contact area between metals and graphene has different influences on the conductance. The Cu-graphene system shows an increase in differential conductance for more contact area at a low bias voltage, primarily originating from the shift of transmission peaks relative to the Fermi energy. As the bias increases, there is an irregular change of conductance, including a weak negative differential conductance for more contact area. In contrast, the conductance of the Ni-graphene junction is monotonically enhanced with increasing overlap area. The minority spin which shows a broad transmission is responsible for the conductance increase of Ni-graphene. These behaviors can be attributed to different mechanisms of the interfacial electron transport: Charge transfer between graphene and Cu largely dominates the transmission enhancement of Cu-graphene, whereas hybridization between graphene and Ni states plays a more important role in the transmission enhancement of Ni-graphene. The different behaviors of transmission increase correlate with not only the strength of the graphene-metal interaction but also the location of metal d states.
我们对扶手椅型石墨烯纳米带在不同接触面积下吸附在 Cu(111)和 Ni(111)表面上的电子输运进行了第一性原理研究。我们发现金属和石墨烯之间的接触面积对电导有不同的影响。在低偏压下，Cu-石墨烯系统的微分电导随接触面积的增加而增加，主要源于传输峰相对于费米能级的移动。随着偏压的增加，电导呈现不规则的变化，包括较大接触面积时的弱负微分电导。相比之下，Ni-石墨烯结的电导随重叠面积的增加而单调增强。少数自旋表现出宽的传输，这是 Ni-石墨烯电导增加的原因。这些行为可以归因于界面电子输运的不同机制：石墨烯和 Cu 之间的电荷转移在很大程度上主导了 Cu-石墨烯的传输增强，而石墨烯和 Ni 态之间的杂化在 Ni-石墨烯的传输增强中起着更重要的作用。传输增强的不同行为不仅与石墨烯-金属相互作用的强度有关，还与金属 d 态的位置有关。
