Graphene is a two-dimensional carbon material with a honeycomb lattice and Dirac-like low-energy excitations. When Zeeman and spin-orbit interactions are neglected, its Landau levels are fourfold degenerate, explaining the 4e2/h separation between quantized Hall conductivity values seen in recent experiments. In this Letter we derive a criterion for the occurrence of interaction-driven quantum Hall effects near intermediate integer values of e2/h due to charge gaps in broken symmetry states.

Quantum Hall Ferromagnetism in Graphene

Confined Synthesis of 2D Nanostructured Materials toward Electrocatalysis

We demonstrate theoretically that most of the observed transport properties of graphene sheets at zero magnetic field can be explained by scattering from charged impurities. We find that, contrary to common perception, these properties are not universal but depend on the concentration of charged impurities nimp. For dirty samples (250 × 1010 cm−2 < nimp < 400 × 1010 cm−2), the value of the minimum conductivity at low carrier density is indeed 4e2/h in agreement with early experiments, with weak dependence on impurity concentration. For cleaner samples, we predict that the minimum conductivity depends strongly on nimp, increasing to 8e2/h for nimp ≈ 20 × 1010 cm−2. A clear strategy to improve graphene mobility is to eliminate charged impurities or use a substrate with a larger dielectric constant.

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A self-consistent theory for graphene transport.

Graphene is a material with unique properties that can be exploited in electronics, catalysis, energy, and bio-related fields Although, for maximal utilization of this material, high-quality graphene is required at both the growth process and after transfer of the graphene film to the application-compatible substrate Chemical vapor deposition (CVD) is an important method for growing high-quality graphene on non-technological substrates (as, metal substrates, eg, copper foil) Thus, there are also considerable efforts toward the efficient and non-damaging transfer of quality of graphene on to technologically relevant materials and systems In this review article, a range of graphene current transfer techniques are reviewed from the standpoint of their impact on contamination control and structural integrity preservation of the as-produced graphene In addition, their scalability, cost- and time-effectiveness are discussed We summarize with a perspective on the transfer challenges, alternative options and future developments toward graphene technology

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Graphene transfer methods: A review

The transfer process is crucial for obtaining high-quality graphene for its large-scale industrial application. In this review, graphene transfer methods are systematically classified along with an analysis of the contamination or impurity of graphene that is introduced during the transfer process. Two key processes are emphasized, the substrate removal process and the direct/indirect transfer of graphene. Based on the efficiency and cost factors of industrial scale production, various transfer methods are summarized and evaluated. Potential transfer technologies and future research directions for industrial application are prospected.

Towards large-scale graphene transfer

Synthesis of large-area graphene films on rolled-up Cu foils by a “breathing” method

Expected for many promising applications in the field of electronics and optoelectronics, a reliable method for the characterization of graphene electrical transport properties is desired to predict its device performance or provide feedback for its synthesis. However, the commonly used methods of extracting carrier mobility from graphene field effect transistor or Hall-bar is time consuming, expensive, and significantly affected by the device fabrication process other than graphene itself. Here we reported a general and simple method to evaluate the electrical transport performance of graphene by the van der Pauw–Hall measurement. By annealing graphene in vacuum to remove the adsorbed dopants and then exposing it in ambient surroundings, carrier mobility as a function of density can be measured with the increase of carrier density due to the dopant re-adsorption from the surroundings. Further, the relationship between the carrier mobility and density can be simply fitted with a power equation to the first level approximation, with which any pair of measured carrier mobility and density can be normalized to an arbitrary carrier density for comparison. We experimentally demonstrated the reliability of the method, which is much simpler than making devices and may promote the standard making for graphene characterization.

A general and simple method for evaluating the electrical transport performance of graphene by the van der Pauw-Hall measurement

The invention discloses a suspended graphene transfer method, and belongs to the technical field of suspended graphene preparation. The method comprises the following steps: 1) fixing a mask materialon a metal substrate on which graphene grows by a chemical vapor deposition method, and evaporating metal above the graphene; 2) after metal evaporation is completed, removing the mask material, placing the structural layer with the metal/graphene/metal substrate in etching liquid to etch the metal substrate to form the structural layer with the metal/graphene; and 3) rinsing the structural layerwith the metal/graphene, then fishing out the structural layer with the metal/graphene by adopting a hollow substrate, and drying the product. According to the method, metal evaporation is carried outon the surface of the graphene by adopting various mask materials, exposed graphene with different areas can be obtained after the mask materials are fixed on the surface of the graphene for metal evaporation, graphene with different suspension areas can be obtained after etching transfer, and area-controllable suspension graphene transfer is realized.

Yuting Niu

Papers

Towards large-scale graphene transfer

Synthesis of large-area graphene films on rolled-up Cu foils by a “breathing” method

A general and simple method for evaluating the electrical transport performance of graphene by the van der Pauw-Hall measurement

Suspended graphene transfer method