Graphene-based materials are promising candidates for nanoelectronic devices because very high carrier mobilities can be achieved without the use of sophisticated material preparation techniques. However, the carrier mobilities reported for single-layer and bilayer graphene are still less than those reported for graphite crystals at low temperatures, and the optimum number of graphene layers for any given application is currently unclear, because the charge transport properties of samples containing three or more graphene layers have not yet been investigated systematically. Here, we study charge transport through trilayer graphene as a function of carrier density, temperature, and perpendicular electric field. We find that trilayer graphene is a semimetal with a resistivity that decreases with increasing electric field, a behaviour that is markedly different from that of single-layer and bilayer graphene. We show that the phenomenon originates from an overlap between the conduction and valence bands that can be controlled by an electric field, a property that had never previously been observed in any other semimetal. We also determine the effective mass of the charge carriers, and show that it accounts for a large part of the variation in the carrier mobility as the number of layers in the sample is varied.

Future wearable electronics, displays and photovoltaic devices require materials which are mechanically flexible, lightweight and low-cost, in addition to being electrically conductive and optically transparent [1][2][3]. Nowadays indium tin oxide (ITO) is the most wide spread

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We present a comparative study of high carrier density transport in mono-, bi-, and trilayer graphene using electric double-layer transistors to continuously tune the carrier density up to values exceeding 10 14 cm −2 . Whereas in monolayer the conductivity saturates, in bi-and trilayer filling of the higher-energy bands is observed to cause a nonmonotonic behavior of the conductivity and a large increase in the quantum capacitance. These systematic trends not only show how the intrinsic high-density transport properties of graphene can be accessed by field effect, but also demonstrate the robustness of ion-gated graphene, which is crucial for possible future applications.T he investigation of transport through graphene layers has been focusing almost exclusively on the low carrier density regime (n ∼ 10 12 cm −2 ), where electrons behave as chiral particles and unexpected physical phenomena occur (1, 2). Despite exciting theoretical predictions (possible occurrence of superconductivity; refs. 3-5) and its clear relevance for technological applications (transparent electrodes for flat panel displays, ref. 6, supercapacitors, ref. 7, and biosensors, ref. 8), the high carrier density regime (n ∼ 10 14 cm −2 ) has remained vastly unexplored due to the limited amount of carrier density accessible in conventional solid-state field-effect transistors (9, 10). The recent development of so-called ionic-liquid gates, in which the coupling between gate electrode and transistor channel is effectively realized through moving ions that form an electric double layer (EDL) at the liquid/channel interface ( Fig. 1A), is now changing the situation. The gate voltage applied-up to several voltsdrops across a very large geometrical EDL capacitance of approximately 1-nm thick. As a result, the induced carrier density can easily exceed n 2D ≈ 10 14 cm −2 , more than one order of magnitude larger than that in conventional solid-state field-effect transistors (FETs). Such a very strong field effect is valuable for technological applications (for instance, in organic FETs, ref. 11, where it enables low-voltage operation) and as a versatile and effective tool to tune electronic states in a rich variety of systems (by modulating metal insulator transition, ref. 12, magnetoresistance, ref. 13, and by inducing superconductivity at the surface of insulators, refs. 14 and 15).Recent works show that ion gating can also be used in combination with graphene. Experiments (e.g., Raman spectroscopy, ref. 16, quantum capacitance, ref. 17, transport, refs. 18 and 19, etc.) have focused almost exclusively on properties of monolayer, but no characteristic high carrier density features in the transport properties were identified. Here, as an efficient strategy to reveal these characteristic features, we perform a comparative study of transport in ion-gated mono-, bi-, and trilayer graphene at high carrier density of approximately 10 14 cm −2 . The motivation for this strategy is twofold. First, when n 2D exceeds values of several 10 13 cm −2 , differ...

We demonstrate the possibility to selectively reduce insulating fluorinated graphene to conducting and semiconducting graphene by electron beam irradiation. Electron-irradiated fluorinated graphene microstructures show 7 orders of magnitude decrease in resistivity (from 1 TΩ to 100 kΩ), whereas nanostructures show a transport gap in the source-drain bias voltage. In this transport gap, electrons are localized, and charge transport is dominated by variable range hopping. Our findings demonstrate a step forward to all-graphene transparent and flexible electronics.