Probing top-gated field effect transistor of reduced graphene oxide monolayer made by dielectrophoresis

We demonstrate a top-gated field effect transistor made of a reduced graphene oxide (RGO) monolayer (graphene) by dielectrophoresis. The Raman spectrum of RGO flakes of typical size of 5μm×5μm shows a single 2D band at 2687 cm−1, characteristic of single-layer graphene. The two-probe current–voltage measurements of RGO flakes, deposited in between the patterned electrodes with a gap of 2.5 μm using ac dielectrophoresis, show ohmic behavior with a resistance of ∼37kΩ. The temperature dependence of the resistance (R)(R) of RGO measured between 305 K and 393 K yields a temperature coefficient of resistance [dR/dT]/R∼−9.5×10−4/K, the same as that of mechanically exfoliated single-layer graphene. The field-effect transistor action was obtained by electrochemical top-gating using a solid polymer electrolyte (PEO+LiClO4) and Pt wire. The ambipolar nature of graphene flakes is observed up to a doping level of ∼6×1012/cm2 and carrier mobility of ∼50 cm2/V s. The source–drain current characteristics show a tendency of current saturation at high source–drain voltage which is analyzed quantitatively by a diffusive transport model.