(bottom) Schematic of the device with the floating metal on the graphene channel, showing two current flow paths. (top) Schematic of the contact region, showing the transfer length (dT ).
(a) Optical micrograph of the fabricated monolayer graphene FET device showing the four metal electrodes on the graphene channel. The contact metal was Ni, and ohmic contacts were confirmed for all electrodes. (b) Schematic top and side views of the device for extracting the resistivity of the graphene/metal double-layered structure.
(a) Intrinsic graphene resistivity (ρG ) and R 1 for various LM as a function of VG . (b) Sheet resistivities of intrinsic graphene channel (ρG ) and graphene/metal double-layers with various LM as a function of VG .
Resistor network model for the device in Fig. 2 .
(a) Current flow ratio in graphene (IG /Iin ) calculated at LM = 1 μm and VG = DP for various ρC . The larger ρC prevents the current from flowing into the metal. (b) Current flow ratio in graphene (IG /Iin ) calculated at ρC = 1× 103 Ω μm2 and VG = DP for various LM . The current flow ratio in graphene increases with decreasing LM .
Calculated sheet resistivities for the graphene/metal double-layered structure using the experimental value of ρG , where the DP shift is not considered.
(a) Optical micrograph and (b) schematic of the bilayer-graphene FET device for direct measurements. The shape of graphene was etched by O2 plasma before the metal deposition; three sets of voltage probes A–C are shown.
(a) Sheet resistivities of intrinsic bilayer graphene channel (ρG ) and graphene/metal double-layered structure with various positions. A–C indicate measured positions in Fig. 7(b) . (b) Calculated sheet resistivities for the graphene/metal double-layered structure using the experimental value of ρG , where the DP shift is not considered. D is the calculation result from the voltage difference between 0 μm and 1 μm from the metal edge.
Relationship between work function for various metals and doping polarity in graphene reported in the literature. The ideal doping polarity is hatched based on the work function difference between graphene (4.5 eV) and metals. White circles indicate the doping polarity judged from the asymmetry of the current-gate voltage curve, while gray circles indicate the doping polarity judged from the DP shift when metal particles are deposited on the graphene channel. The numbers in the circles show the references ( 24–37 ) and “P” indicates the present results.
(a) Optical micrograph of graphene on the SiO2 substrate. The EBSP orientation map of the normal direction (ND) is colored using the inverse pole figure triangle. Both the ND and the transverse direction (TD) show a single color, which suggests that Ni(111) grew epitaxially on the graphene. (b) Optical micrograph of the graphene FET device with a Ni electrode on the channel. The EBSP orientation map of the ND is colored using the inverse pole figure triangle.
(a) Optical micrograph of the device fabricated with a resist-free process using a Si wafer mask. Thick Ni ∼15 nm, thin Ni ∼4 nm. (b) Schematic of the VG -dependent Raman measurement system, where the thick Ni was directly contacted by the W prober tip. An objective lens (×50) with a long working distance was used.
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