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Graphene was grown directly on porous nickel films, followed by the growth of controlled lengths of vertical carbon nanotube (CNT) forests that seamlessly emanate from the graphene surface. The metal–graphene–CNT structure is used to directly fabricate field-emitter devices and double-layer capacitors. The three-dimensional nanostructured hybrid materials, with better interfacial contacts and volume utilization, can stimulate the development of several energy-efficient technologies.

Graphene and single-walled carbon nanotubes are carbon materials that exhibit excellent electrical conductivities and large specific surface areas. Theoretical work suggested that a covalently bonded graphene/single-walled carbon nanotube hybrid material would extend those properties to three dimensions, and be useful in energy storage and nanoelectronic technologies. Here we disclose a method to bond graphene and single-walled carbon nanotubes seamlessly during the growth stage. The hybrid material exhibits a surface area2,000 m(2) g(-1) with ohmic contact from the vertically aligned single-walled carbon nanotubes to the graphene. Using aberration-corrected scanning transmission electron microscopy, we observed the covalent transformation of sp(2) carbon between the planar graphene and the single-walled carbon nanotubes at the atomic resolution level. These findings provide a new benchmark for understanding the three-dimensional graphene/single-walled carbon nanotube-conjoined materials.

Few-layer graphene, with Bernal stacking order, is of particular interest to the graphene community because of its unique tunable electronic structure. A synthetic method to produce such large area graphene films with precise thickness from 2 to 4 layers would be ideal for chemists and physicists to explore the promising electronic applications of these materials. Here, large-area uniform Bernal-stacked bi-, tri-, and tetralayer graphene films were successfully synthesized on a Cu surface in selective growth windows, with a finely tuned total pressure and CH(4)/H(2) gas ratio. On the basis of the analyses obtained, the growth mechanism is not an independent homoexpitaxial layer-by-layer growth, but most likely a simultaneous-seeding and self-limiting process.

We have fabricated a centimeter-size single-layer graphene device with a gate electrode, which can modulate the transmission of terahertz and infrared waves. Using time-domain terahertz spectroscopy and Fourier-transform infrared spectroscopy in a wide frequency range (10-10 000 cm(-1)), we measured the dynamic conductivity change induced by electrical gating and thermal annealing. Both methods were able to effectively tune the Fermi energy, E(F), which in turn modified the Drude-like intraband absorption in the terahertz as well as the "2E(F) onset" for interband absorption in the mid-infrared. These results not only provide fundamental insight into the electromagnetic response of Dirac fermions in graphene but also demonstrate the key functionalities of large-area graphene devices that are desired for components in terahertz and infrared optoelectronics.

Using ultrahigh magnetic fields up to 170 T and polarized midinfrared radiation with tunable wavelengths from 9.22 to 10.67 um, we studied cyclotron resonance in large-area graphene grown by chemical vapor deposition. Circular-polarization dependent studies reveal strong p-type doping for as-grown graphene, and the dependence of the cyclotron resonance on radiation wavelength allows for a determination of the Fermi energy. Thermal annealing shifts the Fermi energy to near the Dirac point, resulting in the simultaneous appearance of hole and electron cyclotron resonance in the magnetic quantum limit, even though the sample is still p-type, due to graphene's linear dispersion and unique Landau level structure. These high-field studies therefore allow for a clear identification of cyclotron resonance features in large-area, low-mobility graphene samples., 9 pages, 3 figures

We use terahertz time-domain spectroscopy and Fourier-transform infrared spectroscopy to investigate carrier dynamics in large-area chemical-vapor-deposition-grown graphene, and observed that the Fermi level of graphene can be tuned by both thermal annealing and electrical gating.

Here we demonstrate a general transfer-free method to directly grow large areas of uniform bilayer graphene on insulating substrates (SiO(2), h-BN, Si(3)N(4), and Al(2)O(3)) from solid carbon sources such as films of poly(2-phenylpropyl)methysiloxane, poly(methyl methacrylate), polystyrene, and poly(acrylonitrile-co-butadiene-co-styrene), the latter leading to N-doped bilayer graphene due to its inherent nitrogen content. Alternatively, the carbon feeds can be prepared from a self-assembled monolayer of butyltriethoxysilane atop a SiO(2) layer. The carbon feedstocks were deposited on the insulating substrates and then caped with a layer of nickel. At 1000 °C, under low pressure and a reducing atmosphere, the carbon source was transformed into a bilayer graphene film on the insulating substrates. The Ni layer was removed by dissolution, affording the bilayer graphene directly on the insulator with no traces of polymer left from a transfer step. The bilayer nature of as-grown samples was demonstrated by I(G)/I(2D) Raman mapping, the statistics of the full-width at half-maximum of the Raman 2D peak, the selected area electron diffraction patterns over a large area, and randomly imaged graphene edges by high-resolution transmission electron microscopy.

Here we report a transfer-free method of synthesizing bilayer graphene directly on SiO(2) substrates by carbon diffusion through a layer of nickel. The 400 nm nickel layer was deposited on the top of SiO(2) substrates and used as the catalyst. Spin-coated polymer films such as poly(methyl methacrylate), high-impact polystyrene or acrylonitrile-butadiene-styrene, or gas-phase methane were used as carbon sources. During the annealing process at 1000 °C, the carbon sources on the top of the nickel decomposed and diffused into the nickel layer. When cooled to room temperature, bilayer graphene was formed between the nickel layer and the SiO(2) substrates. The nickel films were removed by etchants, and bilayer graphene was then directly obtained on SiO(2), eliminating any transfer process. The bilayer nature of the obtained graphene films on SiO(2) substrates was verified by Raman spectroscopy and transmission electron microscopy. The Raman spectroscopy mapping over a 100 × 100 μm(2) area indicated that the obtained graphene is high-quality and bilayer coverage is approximately 70%.

The controllable and reversible modification of graphene by chemical functionalization can modulate its optical and electronic properties. Here we demonstrate the controlled patterning of graphane/graphene superlattices within a single sheet of graphene. By exchanging the sp3 C–H bonds in graphane with sp3 C–C bonds through functionalization, sophisticated multifunctional superlattices can be fabricated on both the macroscopic and microscopic scales. These patterns are visualized using fluorescence quenching microscopy techniques and confirmed using Raman spectroscopy. By tuning the extent of hydrogenation, the density of the sp3 C functional groups on graphene's basal plane can be controlled from 0.4% to 3.5% with this two-step method. Using such a technique, which allows for both spatial and density control of the functional groups, a route to multifunctional electrical circuits and chemical sensors with specifically patterned recognition sites might be realized across a single graphene sheet, facilitating the development of graphene-based devices. The controllable modification of graphene by chemical functionalization can modulate its optical and electronic properties. Sunet al. devise a functionalisation-based method to pattern graphane/graphene superlattices within a single sheet of graphene.

We demonstrate the water-assisted supergrowth of vertically aligned single-walled carbon-nitrogen nanotubes (SWNNTs) using a simple liquid/gas-phase precursor system. In situ characterization of gas-phase nitrogen-containing precursors and their correlation to growth identifies HCN as the most active precursor for SWNNT growth, analogous to C(2)H(2) for single-walled carbon nanotubes (SWNTs). Utilizing Raman spectroscopy, combined with XPS and in situ mass spectrometry during growth, we demonstrate the ability to probe N atoms at low concentrations (10(-5) at. % N) in the SWNNT. Additionally, we demonstrate sensitivity of SWNNT optical transitions to N-doping through absorbance measurements, which appear to be a sensitive fingerprint for SWNNT doping. Finally, we demonstrate the fabrication of SWNT/SWNNT heterojunctions in the self-assembled carpet morphology that can be printed to arbitrary host substrates and facilitate potential emerging applications for this material. This work brings together new aspects regarding the growth, characterization, and materials processing that can yield advanced material architectures involving electronically tuned SWNNT array networks.

Here we demonstrate that graphene nanoribbons (GNRs) free of oxidized surfaces can be prepared in large batches and 100% yield by splitting multiwalled carbon nanotubes (MWCNTs) with potassium vapor. If desired, exfoliation is attainable in a subsequent step using chlorosulfonic acid. The low-defect density of these GNRs is indicated by their electrical conductivity, comparable to that of graphene derived from mechanically exfoliated graphite. The possible origins of directionally selective splitting of MWCNTs have been explored using computer modeling, and plausible explanations for the unique role of potassium were found.

This paper reports a bottom-up solution-phase process for the preparation of pristine and heteroatom (boron, phosphorus, or nitrogen)-substituted carbon scaffolds that show good surface areas and enhanced hydrogen adsorption capacities and binding energies. The synthesis method involves heating chlorine-containing small organic molecules with metallic sodium at reflux in high-boiling solvents. For heteroatom incorporation, heteroatomic electrophiles are added to the reaction mixture. Under the reaction conditions, micrometer-sized graphitic sheets assembled by 3−5 nm-sized domains of graphene nanoflakes are formed, and when they are heteroatom-substituted, the heteroatoms are uniformly distributed. The substituted carbon scaffolds enriched with heteroatoms (boron ~7.3%, phosphorus ~8.1%, and nitrogen ~28.1%) had surface areas as high as 900 m^2 g^(−1) and enhanced reversible hydrogen physisorption capacities relative to pristine carbon scaffolds or common carbonaceous materials. In addition, the binding energies of the substituted carbon scaffolds, as measured by adsorption isotherms, were 8.6, 8.3, and 5.6 kJ mol^(−1) for the boron-, phosphorus-, and nitrogen-enriched carbon scaffolds, respectively.

An improved method is described for the production of graphene oxide nanoribbons (GONRs) via longitudinal unzipping of multiwalled carbon nanotubes. The method produces GONRs with fewer defects and/or holes on the basal plane, maintains narrow ribbons

Nature 468, 549–552 (2010) In this Letter, the assigned values for melamine XPS signals of 284.5 eV (C 1s) and 395.8 eV (N 1s) were incorrect (Supplementary Fig. 7). Repeating the melamine spectrum with a graphite additive standard (C 1s = 284.5 eV) showed that the assignments for melamine should be286.

α-FeOOH nanocrystals were synthesized in high yield via a facile and template-free hydrothermal method at low temperature. The morphology and composition of the samples were controlled by slowly releasing the SO42− ions from ammonium persulfate. The rod-like, bundle-like, and urchin-like α-FeOOH nanocrystals could be acquired respectively through a direct hydrothermal route with different quantities of SO42− ions. The rod-like α-FeOOH nanocrystals obtained have a diameter of 5–25 nm and a length of 100–200 nm. When the molar ratio of iron to SO42− was 1:1, the product was pure α-FeOOH phase. However, as the molar ratio was decreased from 1:1 to 1:4, pure FeSO4OH·2H2O phase was obtained. When the molar ratio was between 1:4 and 1:1, the prepared product was composed of two phases (α-FeOOH and FeSO4OH·2H2O). After hydrothermally aging the as-synthesized α-FeOOH nanorods at 180 °C for 1 d, α-Fe2O3 nanorods were obtained. However, the edge of the α-Fe2O3 nanorods was sword-like and different from the blunt edge of α-FeOOH nanorods due to a recrystallization mechanism.

Polypyrrole (PPy)/PB and PPy/Ag composite microtubes were synthesized in one pot by using methyl orange (MO) as a reactive self-degraded template. In contrast to reported conventional template approaches, the MO template did not need to be removed after polymerization. The formation mechanism, structural characteristics, conductivity, and electrochemical properties of the obtained PPy/PB and PPy/Ag microtubes are reported.