Every few years, a new material with unique properties emerges and fascinates the scientific community, typical recent examples being high-temperature superconductors and carbon nanotubes. Graphene is the latest sensation with unusual properties, such as half-integer quantum Hall effect and ballistic electron transport. This two-dimensional material which is the parent of all graphitic carbon forms is strictly expected to comprise a single layer, but there is considerable interest in investigating two-layer and few-layer graphenes as well. Synthesis and characterization of graphenes pose challenges, but there has been considerable progress in the last year or so. Herein, we present the status of graphene research which includes aspects related to synthesis, characterization, structure, and properties.

Graphene has emerged as an exciting material because of the novel properties associated with its two-dimensional structure. [1,2] Single-layer graphene is a one-atom thick sheet of carbon atoms densely packed into a two-dimensional honeycomb lattice. It is the mother of all graphitic forms of carbon, including zero-dimensional fullerenes and one-dimensional carbon nanotubes.[1] The remarkable feature of graphene is that it is a Dirac solid, with the electron energy being linearly dependent on the wave vector near the vertices of the hexagonal Brillouin zone. It exhibits a room-temperature fractional quantum Hall effect [3] and an ambipolar electric field effect along with ballistic conduction of charge carriers.[4] It has been reported recently that a top-gated single-layer graphene transistor is able to reach electron-or hole-doping levels of upto 5 Â 10 13 cm À2 . The doping effects are ideally monitored by Raman spectroscopy. [5][6][7][8][9][10] Thus, the G-band in the Raman spectrum stiffens for both electron-and hole-doping, and the ratio of the intensities of the 2D-and G-band varies sensitively with doping. Doping graphene through molecular charge-transfer caused by electron-donor and -acceptor molecules also gives rise to significant changes in the electronic structure of graphenes composed of a few layers, as evidenced by changes in the Raman and photoelectron spectra. [6,7] Charge-transfer by donor and acceptor molecules soften and stiffen the G-band, respectively. The difference between electrochemical doping and doping through molecular charge-transfer is noteworthy. It is of fundamental interest to investigate how these effects compare with the effects of doping graphene by substitution with boron and nitrogen and to understand dopant-induced perturbations of the properties of graphene. Secondly, opening the bandgap in graphene is essential for facilitating its applications in electronics, and graphene bilayers [11] are an attractive option for this. With this motivation, we prepared, for the first time, B-and N-doped graphene (BG and NG) bilayer samples by employing different strategies and investigated their structure and properties. We also carried out first-principles density functional theory (DFT) calculations to understand the effect of substitutional doping on the structure of graphene as well as its electronic and vibrational properties.To prepare BGs and NGs, we exploited our recent result in which it was determined that arc discharge between carbon electrodes in a hydrogen atmosphere yields graphenes (HG) composed of two to three layers.[12] The method makes use of the fact that in the presence of hydrogen, graphene sheets do not readily roll into nanotubes. In the case of BG, we carried out the arc discharge using graphite electrodes in the presence H 2 þ B 2 H 6 (BG1) or using boron-stuffed graphite electrodes (BG2). We prepared NG by carrying out the arc discharge in the presence of H 2 þ pyridine (NG1) or H 2 þ ammonia (NG2). We also performed the transformation of nanodiamond in th...

Graphenes prepared by three different methods have been investigated as electrode materials in electrochemical supercapacitors. The samples prepared by exfoliation of graphitic oxide and by the transformation of nanodiamond exhibit high specific capacitance in aq. H 2 SO 4 , the value reaching up to 117 F/g. By using an ionic liquid, the operating voltage has been extended to 3⋅5 V (instead of 1 V in the case of aq. H 2 SO 4 ), the specific capacitance and energy density being 75 F/g and 31⋅9 Wh kg -1 respectively. This value of the energy density is one of the highest values reported to date. The performance characteristics of the graphenes which are directly related to the quality, in terms of the number of layers and the surface area, are superior to that of single-walled and multi-walled carbon nanotubes.

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Graphene has been prepared by different methods: pyrolysis of camphor under reducing conditions (CG), exfoliation of graphitic oxide (EG), conversion of nanodiamond (DG) and arc evaporation of SiC (SG). The samples were examined by X-ray diffraction (XRD), transmission electron microscopy, atomic force microscopy, Raman spectroscopy and magnetic measurements. Raman spectroscopy shows EG and DG to exhibit smaller in-plane crystallite sizes, but in combination with XRD results EG comes out to be better. The CG, EG and DG samples prepared by us have BET surface areas of 46, 925 and 520 m 2 g À1 respectively and exhibit significant hydrogen uptake up to 3 wt%. EG also exhibits a high CO 2 uptake (34.7 wt%). Electrochemical redox properties of the graphene samples have been examined in addition to their use in electrochemical supercapacitors. Functionalization of EG and DG through amidation has been carried out with the purpose of solubilizing them in non-polar solvents. Water-soluble graphene has been produced by extensive acid treatment of EG or treatment with polyethylene glycol.