Electronic Transport Properties of Individual Chemically Reduced Graphene Oxide Sheets

Gómez-Navarro, Cristina; Weitz, R. Thomas; Bittner, Alexander M.; Scolari, Matteo; Mews, Alf; Burghard, Marko; Kern, Klaus

doi:10.1021/nl072090c

Cited by 2,226 publications

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“…The temperature dependent transfer characteristics in Figure 2c indicate that the on/off ratio of the devices increases with decreasing temperature, a trend that has also been observed for individual monolayer of reduced GO. 18 The on/off ratio with temperature trend observed for FGS-PS thin films suggests that the FGS are well dispersed and remain exfoliated in the PS matrix. The I sd -V sd characteristics of the devices were linear even at 4.2 K, indicating negligible energy barriers at the contacts (Figure 2d).…”

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confidence: 93%

“…3 Conductance modulation by bottom-gating was observed in all measured devices and showed ambipolar field effect similar to reduced GO thin film transistors. 12,18 Field effect mobility was generally higher for holes than for electrons by a factor of about 2∼5 and was generally between 0.1 and 1 cm 2 /Vs in ambient conditions. Unlike reduced GO, the composite devices were weakly sensitive to unintentional ambient doping, suggesting that majority of FGS responsible for the carrier transport are embedded within the PS.…”

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“…That is, there are contributions from thermal activation of carriers, tunneling through PS matrix, and variable range hopping both within and between the FGS. 18 The activation energy obtained above is only a rough estimation of the total energy required for thermal carrier activation and transport.…”

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Graphene-based Composite Thin Films for Electronics

2009

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The electrical properties of solution-processed composite thin films consisting of functionalized graphene sheets (FGS) as the filler and polystyrene (PS) as the host material are described. We demonstrate that transistors from graphene-based composite thin films exhibit ambipolar field effect characteristics, suggesting transport via percolation among FGS in the insulating PS matrix. Device characteristics as a function of the FGS size are also reported. The results indicate that devices fabricated using the largest size FGS yield the highest mobility values. This simple and scaleable fabrication scheme based on a commodity plastic could be useful for low-cost, macro-scale electronics.Graphene-based composites are emerging as new class of materials that hold promise for several applications. 1 Graphene, a single sheet of graphite, possesses extraordinary electrical, thermal, and mechanical properties arising from its unique structure. 2 When incorporated into polymer 3-6 or ceramic 7 matrices, these properties manifest as remarkable improvements in the host material. Graphene-based polymer composites exhibit extraordinarily low electrical percolation threshold (0.1 vol %) due to large conductivity and aspect ratio of the graphene sheets (atomic thickness and micrometersized lateral dimensions). 3,6 The mechanical and thermal properties of these materials rank among the best in comparison with other carbon-based composites due to strong interactions between polymer hosts and graphene sheets. 1,5 The highly conductive nature of graphene and ease of incorporation into polymers and ceramics has also opened up the possibility of their use as transparent conductors. 7 Furthermore, we recently demonstrated that atomically sharp edges of graphene incorporated into a PS host can be exploited for field emission. 8 Graphene is a zero band gap semiconductor exhibiting large electric field effect, 9 allowing doping with electrons or holes via electrostatic gating. The fact that graphene does not have a band gap poses a challenge for digital applications, but its high mobility is attractive for high frequency analog electronics or spintronics. 10,11 The semiconducting and robust mechanical properties of reduced graphene have been exploited for macro-scale thin film electronic devices 12,13 and high performance resonators. 14 Semiconducting behavior has yet to be demonstrated in graphene-based composites. The compatibility of graphene with polymers and ceramics opens up a route toward realization of semiconducting composite materials from electrically passive host materials. That is, introduction of percolating graphene network within an insulating material may render it semiconducting. In this study, we show that incorporation of functionalized graphene sheets (FGS) in polystyrene (PS) matrix results in composite thin films that are semiconducting and exhibit ambipolar field effect. These composites can be deposited uniformly over large areas in the form of thin films from solution onto which devices can be fabricate...

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Graphene-based Composite Thin Films for Electronics

2009

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“…Recently, researchers have circumvented the problem of mechanical cleavage by using graphite oxide (GO), a layered compound that can be readily dispersed as individual sheets in a good solvent. [15][16][17][18][19][20][21][22][23] Although GO itself is not electrically conductive, the conjugated network may be restored upon reduction in hydrazine vapor or with high heat after deposition. 18,21,22 However, both reduction methods have their drawbacks, as high temperatures are incompatible with flexible substrates (e.g., poly(ethylene terephthalate), PET) and hydrazine vapors are only able to access and reduce the outer surface of deposited films.…”

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Low-Temperature Solution Processing of Graphene−Carbon Nanotube Hybrid Materials for High-Performance Transparent Conductors

et al. 2009

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We report the formation of a nanocomposite comprised of chemically converted graphene and carbon nanotubes. Our solution-based method does not require surfactants, thus preserving the intrinsic electronic and mechanical properties of both components, delivering 240 Ω/0 at 86% transmittance. This low-temperature process is completely compatible with flexible substrates and does not require a sophisticated transfer process. We believe that this technology is inexpensive, is massively scalable, and does not suffer from several shortcomings of indium tin oxide. A proof-of-concept application in a polymer solar cell with power conversion efficiency of 0.85% is demonstrated. Preliminary experiments in chemical doping are presented and show that optimization of this material is not limited to improvements in layer morphology.

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“…6,7 Due to the limited efficiency of the reduction process, the obtained sheets still contain residual oxygenated functional groups of the starting material. Microscopic studies of the reduced GO also indicate the coexistence of graphitic regions with defect clusters 6,9 in agreement with proposed models. [9][10][11] In addition to its interesting electrical characteristics, this 2D material is expected to have also unique mechanical properties.…”

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Elastic Properties of Chemically Derived Single Graphene Sheets

2008

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The elastic modulus of freely suspended graphene monolayers, obtained via chemical reduction of graphene oxide, was determined through tip-induced deformation experiments. Despite their defect content, the single sheets exhibit an extraordinary stiffness (E ) 0.25 TPa) approaching that of pristine graphene, as well as a high flexibility which enables them to bend easily in their elastic regime. Built-in tensions are found to be significantly lower compared to mechanically exfoliated graphene. The high resilience of the sheets is demonstrated by their unaltered electrical conductivity after multiple deformations. The electrical conductivity of the sheets scales inversely with the elastic modulus, pointing toward a 2-fold role of the oxygen bridges, that is, to impart a bond reinforcement while at the same time impeding the charge transport.Recent experiments have revealed the thermodynamic stability of graphene under ambient conditions, 1-3 which strongly revived the interest in the electrical and mechanical properties of this fascinating carbon nanostructure. Two major methods have been established for the fabrication of graphene monolayers, namely, mechanical exfoliation of graphite 2 and vacuum graphitization of silicon carbide. 3,4 More recently, chemical reduction of graphene oxide (GO) has been reported as an alternative, solution-based route, for obtaining graphenelike sheets which offers the advantages of being cheap and up-scalable. [5][6][7][8] Even though GO is a good insulator, deoxygenation has been shown to substantially enhance its electrical conductivity, albeit the obtained values of ∼1 S/cm remain 2-3 orders of magnitude below that of pristine graphene. 6,7 Due to the limited efficiency of the reduction process, the obtained sheets still contain residual oxygenated functional groups of the starting material. Microscopic studies of the reduced GO also indicate the coexistence of graphitic regions with defect clusters 6,9 in agreement with proposed models. [9][10][11] In addition to its interesting electrical characteristics, this 2D material is expected to have also unique mechanical properties. Recent studies have witnessed its suitability for the fabrication of composites 12,13 and paperlike materials 14 with excellent mechanical properties. However, in order to promote its application in nanotechnology, the mechanical characterization of single sheets is of upmost relevance.Here we present a study of the mechanical and electrical properties of suspended, chemically reduced GO single sheets. Graphite oxide prepared via Hummers method 15 was dispersed in water, deposited onto a Si/SiO 2 substrate, and subsequently reduced by hydrogen plasma treatment. The obtained samples exhibited a high yield of monolayers with lateral dimensions of 0.1-5 µm. Preselected layers were then contacted by standard e-beam lithography with Ti/Au electrodes. In order to freely suspend the layers (Figure 1), the samples were wet etched by buffered hydrofluoric acid, followed by critical point drying to prevent ...

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Electronic Transport Properties of Individual Chemically Reduced Graphene Oxide Sheets

Cited by 2,226 publications

References 28 publications

Graphene-based Composite Thin Films for Electronics

Graphene-based Composite Thin Films for Electronics

Low-Temperature Solution Processing of Graphene−Carbon Nanotube Hybrid Materials for High-Performance Transparent Conductors

Elastic Properties of Chemically Derived Single Graphene Sheets

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