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(a) Schematic of the metal/graphene/SiO2/n+-Si device. (b) Color plot of the optical contrast for graphene on the thin SiO2/Si substrate calculated as functions of wavelength and . The white line indicates the zero contrast. (c) Schematic of the capacitor with graphene (side view) and its equivalent circuit. (d) Schematic of the capacitor without graphene (side view) and its equivalent circuit.
(a) Schematic of the position adjustment system for the PMMA mask and graphene. The position of the PMMA mask pattern can be adjusted relative to that of graphene by the xyzθ stage driven by the stepping motor. (b) (Top) The PMMA stencil mask supported by the Si substrate with a 200-μm square window. (Bottom) Optical image of the C-V device with and without graphene. (c) (Top) The SiN stencil mask supported by the Si substrate with a 200-μm square window. The TLM pattern was fabricated by the FIB instrument. (Bottom) Optical image of the I-V device with the TLM structure fabricated by the resist-free metal deposition technique. The electrodes are always numbered sequentially from 1, which represents the shortest channel.
Total capacitance as a function of VTG for the (a) resist-free Ni, (b) resist-processed Ni, and (c) resist-free Au devices. The blue data are obtained from the device with graphene in Fig. 1(c) , while the red data are obtained from the device without graphene in Fig. 1(d) . (d) The experimentally extracted CQ of graphene with the theoretical line. Solid circles with green, red, and blue colors represent the resist-processed Ni, resist-free Ni, and resist-free Au devices, respectively. The black circle represents the CQ of graphene obtained from the Y2O3 topgate device as a reference. 21 The arrows indicate the highest DOS for the three devices. (e) Summary of the metal/graphene interaction suggested from the CQ measurements.
Two probe resistances as a function of VBG for different channel lengths for the (a) resist-free Ni, (b)resist-processed Ni and (c) resist-free Au devices. The pair of numbers indicates the electrode number shown in Fig. 2(c) . (d) VDP as a function of the channel distance for Ni electrode devices. LCT is the charge transfer length. (e) Summary of the ρc values determined in the present study. (f) Relationship between ρc and the inverse of the DOS, where the largest DOS, shown by the arrows in Fig. 3(d) , was selected.
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