Fig. 2. (Color online) (a–d) Electrical properties of graphene in various devices. All drain currents were measured with a drain voltage of 1 mV. (a) Transfer curve of the EP device before (violet) and after (magenta) heat treatment. (b) Transfer curve of the EM device before (orange) and after (green) heat treatment. (c) Transfer curve of the LP device before (brown) and after (red) heat treatment. (d) Transfer curve of the LM device before (gray) and after (blue) heat treatment. All solid lines and dashed lines in the transfer curve represent a forward sweep and backward sweep of the gate bias, respectively. (e–h) AFM topography images of graphene sheet on SiO2 substrate treated with various processes. Left and right images show graphene surface before and after annealing at 200 °C for an hour under a low vacuum condition, respectively. All scale bars represent a length of 2 μm.
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