Problems associated with large-scale pattern growth of graphene constitute one of the main obstacles to using this material in device applications. Recently, macroscopic-scale graphene films were prepared by two-dimensional assembly of graphene sheets chemically derived from graphite crystals and graphene oxides. However, the sheet resistance of these films was found to be much larger than theoretically expected values. Here we report the direct synthesis of large-scale graphene films using chemical vapour deposition on thin nickel layers, and present two different methods of patterning the films and transferring them to arbitrary substrates. The transferred graphene films show very low sheet resistance of approximately 280 Omega per square, with approximately 80 per cent optical transparency. At low temperatures, the monolayers transferred to silicon dioxide substrates show electron mobility greater than 3,700 cm(2) V(-1) s(-1) and exhibit the half-integer quantum Hall effect, implying that the quality of graphene grown by chemical vapour deposition is as high as mechanically cleaved graphene. Employing the outstanding mechanical properties of graphene, we also demonstrate the macroscopic use of these highly conducting and transparent electrodes in flexible, stretchable, foldable electronics.

The outstanding electrical, mechanical and chemical properties of graphene make it attractive for applications in flexible electronics. However, efforts to make transparent conducting films from graphene have been hampered by the lack of efficient methods for the synthesis, transfer and doping of graphene at the scale and quality required for applications. Here, we report the roll-to-roll production and wet-chemical doping of predominantly monolayer 30-inch graphene films grown by chemical vapour deposition onto flexible copper substrates. The films have sheet resistances as low as approximately 125 ohms square(-1) with 97.4% optical transmittance, and exhibit the half-integer quantum Hall effect, indicating their high quality. We further use layer-by-layer stacking to fabricate a doped four-layer film and measure its sheet resistance at values as low as approximately 30 ohms square(-1) at approximately 90% transparency, which is superior to commercial transparent electrodes such as indium tin oxides. Graphene electrodes were incorporated into a fully functional touch-screen panel device capable of withstanding high strain.

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This Review focuses on noncovalent functionalization of graphene and graphene oxide with various species involving biomolecules, polymers, drugs, metals and metal oxide-based nanoparticles, quantum dots, magnetic nanostructures, other carbon allotropes (fullerenes, nanodiamonds, and carbon nanotubes), and graphene analogues (MoS2, WS2). A brief description of π-π interactions, van der Waals forces, ionic interactions, and hydrogen bonding allowing noncovalent modification of graphene and graphene oxide is first given. The main part of this Review is devoted to tailored functionalization for applications in drug delivery, energy materials, solar cells, water splitting, biosensing, bioimaging, environmental, catalytic, photocatalytic, and biomedical technologies. A significant part of this Review explores the possibilities of graphene/graphene oxide-based 3D superstructures and their use in lithium-ion batteries. This Review ends with a look at challenges and future prospects of noncovalently modified graphene and graphene oxide.

We report variation of the work function for single and bi-layer graphene devices measured by scanning Kelvin probe microscopy (SKPM). Using the electric field effect, the work function of graphene can be adjusted as the gate voltage tunes the Fermi level across the charge neutrality point. Upon biasing the device, the surface potential map obtained by SKPM provides a reliable way to measure the contact resistance of individual electrodes contacting graphene.High conductivity 1,2 and low optical absorption 3,4 make graphene an attractive material for use as a flexible transparent conductive electrode [5][6][7][8] . This atomically thin carbon layer provides the additional benefit that its work function can be adjusted by the electric field effect (EFE). Since the band alignment of two different materials is determined by their respective work functions, control over the graphene work function is the key to reducing the contact barriers of graphene top electrode devices 9, 10 . Previous scanning probe based studies [11][12][13] reveal that the work function of graphene is in a similar range to that of graphite, ~4.6 eV 14 , and depends sensitively on the number of layers 15,16 . However, the active controlling of the graphene work function has yet to be demonstrated.In this study, we apply Scanning Kelvin probe microscope (SKPM) techniques to back-gated graphene devices and demonstrate that the work function can be controlled over a wide range by EFE induced modulation of carrier concentration. SKPM is an atomic force microscope (AFM) based experimental technique that can map the surface potential variation of a sample surface relative to that of metallic tip 17 . The change of work function is ascribed by the Fermi level shift due to the EFE induced carrier doping and is well quantified by the electronic band structure of graphene. On biased graphene devices, SKPM also allows us to accurately measure graphene/metal contact resistances by mapping the surface potential of a device. The wide range of control over the work function demonstrated here suggests graphene as an ideal material for applications where work function optimization is important.Graphene samples were prepared by mechanical exfoliation 18 on Si wafers covered with 300 nm thick SiO 2 and then Cr/Au electrodes (5 nm/30 nm thickness) were fabricated by

Magnetite-graphene hybrids have been synthesized via a chemical reaction with a magnetite particle size of approximately 10 nm. The composites are superparamagnetic at room temperature and can be separated by an external magnetic field. As compared to bare magnetite particles, the hybrids show a high binding capacity for As(III) and As(V), whose presence in the drinking water in wide areas of South Asia has been a huge problem. Their high binding capacity is due to the increased adsorption sites in the M-RGO composite which occurs by reducing the aggregation of bare magnetite. Since the composites show near complete (over 99.9%) arsenic removal within 1 ppb, they are practically usable for arsenic separation from water.

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