Electronic transport properties of atomic scale graphene/metal side contact
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Electronic transport properties of atomic scale graphene/metal side contact Bo Ma,1 Yanwei Wen,1* Xiao Liu,1 and Bin Shan1, 2* 1 School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, Hubei, People’s Republic of China 2 Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, TX 75080, U.S.A. *Corresponding author: [email protected], [email protected] ABSTRACT The transport properties of the atomic scale side contact between different metals (Au, Ag, Pt, Cu, Ni, Pd) and graphene with open zigzag ends have been studied from first-principles electron transport calculations. According to the contact configurations, we find the weakly interacting metals (Au, Ag, Pt and Cu) can form chemical bonds at the open graphene’s atomic edges, while the strongly interacting ones form chemical bonds in the whole contact region. Comparing with the case of end contact which could effectively decrease the contact resistance, the atomic scale side contact shows better transport properties than the end contact. And the graphene/metal side contact with hydrogen terminated graphene edge show obviously large resistance than the ones with open graphene edge, which signifies the importance of the termination of graphene edge in graphene/metal contact. INTRODUCTION Graphene is expected to be a promising material for applications in nano-electronics due to its superior electronic properties and the ultimate thinness. In graphene-based electronic devices, metal–graphene (M-G) contact is a key component for limiting the device performance such as the transconductance, on-current, and cut-off frequency. Many works about M-G contacts have been done to seek for a prefect contact. Intensive theoretical works have studied on the ideal M-G contact interface within firstprinciples calculations, and it is found the metal electrodes could be divided into two types: the weakly interacting metals whose equilibrium interfacial distances is about 3 Å when contacting with graphene, such as Au, Ag, Pt, Cu, and the strongly interacting metals whose equilibrium interfacial distances is less than 2 Å when contacting with graphene, such as Ni, Pd.1-2 And many groups have reported similar conclusion that the strong interaction metal electrodes show less contact resistance than the weak ones.3-6 Novel contact architectures such as using metalgraphene-metal sandwich structures7 or defected graphene,8 have been proposed to increase the interface bonding between the weakly interacting metals (e.g., Cu and Pt) and graphene. Experimental contact resistances (Rc) based on either transfer length measurement (TLM) or a four-probe method show a large device-to-device variation. Especially, some experiments suggested weak interaction metals such as Au, Ag and Cu had low Rc,9-11 which is not consistent with the previously theoretical expectations. One possible reason for the contradiction may be that the effects of the end part and the defects of graphene in actual devices are overlo
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