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The electronic properties of graphene are tunable via doping, making it attractive in low dimensional organic electronics. Common methods of doping graphene, however, adversely affect charge mobility and degrade device performance. We demonstrate a facile shadow mask technique of defining electrodes on graphene grown by chemical vapor deposition (CVD) thereby eliminating the use of detrimental chemicals needed in the corresponding lithographic process. Further, we report on the controlled, effective, and reversible doping of graphene via ultraviolet (UV) irradiation with minimal impact on charge mobility. The change in charge concentration saturates at similar to 2 X 10(12) cm(-2) and the quantum yield is similar to 10(-5) e/photon upon initial UV exposure. This simple and controlled strategy opens the possibility of doping wafer-size CVD graphene for diverse applications. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729828]

We have developed a facile and reliable method to covalently functionalize the surface of graphene field effect transistors (FETs) with polyhistidine-tagged proteins We demonstrated success of chemical functionalization by both atomic force microscopy (AFM) and Raman spectroscopy. Additionally, we characterized the electronic properties of graphene FETs at successive functionalization stages. The specificity enabled by such functionalization, along with the two dimensional nature and intrinsic high sensitivity of graphene, facilitates the emergence of graphene as a promising candidate in surface biochemistry research as well as graphene-based biosensor applications.

The growth of large-area graphene on catalytic metal substrates is a topic of both fundamental and technological interest. We have developed an atmospheric pressure chemical vapor deposition (CVD) method that is potentially more cost-effective and compatible with industrial production than approaches based on synthesis under high vacuum. Surface morphology of the catalytic Cu substrate and the concentration of carbon feedstock gas were found to be crucial factors in determining the homogeneity and electronic transport properties of the final graphene film. The use of an electropolished metal surface and low methane concentration enabled the growth of graphene samples with single layer content exceeding 95%. Field effect transistors fabricated from CVD graphene made with the optimized process had room temperature hole mobilities that are a factor of 2-5 larger than those measured for samples grown on as-purchased Cu foil with larger methane concentration. A kinetic model is proposed to explain the observed dependence of graphene growth on catalyst surface roughness and carbon source concentration.

A method involving the reaction of the commercially available polyborane decaborane with ammonia, that provides a simple chemical vapor deposition (CVD) route for the efficient formation of boron nitride nanosheets (BNNS) on either polycrystalline Ni or Cu foil, was reported. The metal foils were annealed in the CVD system to 1000°C under a combined flow of nitrogen and hydrogen. The AFM analyses in the tapping mode indicate that the films grown on Ni are approx 2 nm thick on average, corresponding to only a few layers of BN graphene. The results show that a fine-tuning of the decaborane/ammonia pressure and growth conditions may likewise result in the controlled growth of regular polygonal BNNS structures on metallic substrates. The Raman spectra of the BNNS confirm the formation of h-BN, showing the characteristic vibration at approx 1366 cm -1 with an intensity that increased as the film thickness is increased.

The properties of a graphene nanostructure are strongly influenced by the arrangement of the atoms on its edge. Growing graphene nanostructures with specified edge types in practical, scalable ways has proven challenging, with limited success to date. Here we report a method for producing graphene flakes with hexagonal shape over large areas, by a brief chemical vapor deposition growth at atmospheric pressure on polished Cu catalyst foil, with limited carbon feedstock. Raman spectra show evidence that the edges of the hexagonal crystallites are predominantly oriented along the zigzag direction. Density functional theory calculations demonstrate that the edge selectivity derives from favorable kinetics of sequential incorporation of carbon atoms to the vacancies in nonzigzag portions of the edges, driving the edges to pure zigzag geometry. This work represents an important step toward realization of graphene electronics with controlled edge geometries, which might find use in digital logic applications or zigzag-edge-based spintronic devices.

We report on DNA translocations through nanopores created in graphene membranes. Devices consist of 1-5 nm thick graphene membranes with electron-beam sculpted nanopores from 5 to 10 nm in diameter. Due to the thin nature of the graphene membranes, we observe larger blocked currents than for traditional solid-state nanopores. However, ionic current noise levels are several orders of magnitude larger than those for silicon nitride nanopores. These fluctuations are reduced with the atomic-layer deposition of 15 nm of titanium dioxide over the device. Unlike traditional solid-state nanopore materials that are insulating, graphene is an excellent electrical conductor. Use of graphene as a membrane material opens the door to a new class of nanopore devices in which electronic sensing and control are performed directly at the pore.

A method is reported to pattern monolayer graphene nanoconstriction field-effect transistors (NCFETs) with critical dimensions below 10 nm. NCFET fabrication is enabled by the use of feedback-controlled electromigration (FCE) to form a constriction in a gold etch mask that is first patterned using conventional lithographic techniques. The use of FCE allows the etch mask to be patterned on size scales below the limit of conventional nanolithography. The opening of a confinement-induced energy gap is observed as the NCFET width is reduced, as evidenced by a sharp increase in the NCFET on/off ratio. The on/off ratios obtained with this procedure can be larger than 1000 at room temperature for the narrowest devices; this is the first report of such large room-temperature on/off ratios for patterned graphene FETs.

Graphene has been shown to have an extraordinary set of electronic properties and its chemical affinity is readily tuned by functionalization with a broad range of molecules. It is known that field effect transistors based on single-layer graphene demonstrate extremely high sensitivity for chemical sensing. It is thus very important to achieve fabrication of integrated circuits on large-area graphene in order to realize practical applications, e.g. an advanced "electronic nose" system. Utilizing recent advances in graphene and graphene oxide preparation and functionalization techniques, we aim to achieve fabrication of sensor arrays using conventional photolithography, where signals from the array are coupled to signal-conditioning electronics and sensor responses fed to odor recognition algorithms to perform detection and classification of vapors.

Arrays of chemical sensors based on homo-oligomer single-stranded DNA (ssDNA) adsorbed to single-walled carbon nanotube field effect transistors (SWNT-FETs) were employed to detect several gaseous analytes. Exposure of these devices to analytes results in a characteristic current shift in the SWNT-FET. The magnitude of this current shift for a particular analyte varies with the base sequence of adsorbed ssDNA and follows the trend d(G)(21)-SWNT > d(A)(21)-SWNT > d(C)(21)-SWNT > d(T)(21)-SWNT. Molecular dynamics simulations suggest that a comparable trend of d(G)(21) > d(A)(21) > d(T)(21)- > d(C)(21) exists for ssDNA-SWNT binding affinities. This indicates that the nature of ssDNA-SWNT binding plays a vital role in the performance of the sensor. Stronger binding implies a greater amount of ssDNA adsorbed to SWNT surface. This would result in a more hydrophilic environment around the hydrophobic SWNT core and thus facilitate the adsorption of polar analytes. (C) 2009 Elsevier Ltd. All rights reserved.

We find layer number dependence in the size of metal nanoparticles grown on 1 to 10 layer graphene. Graphene is an attractive substrate for investigating and using nanoparticles due to its loose interaction with them. To preserve this condition it is ideal to grow particles in place rather than deposit them from solution. We find that annealing of evaporated metal nanoparticles on graphene and few layer graphene surfaces tightens their size distribution. The number of graphene layers changes the selected size. These results are in quantitative agreement with a model incorporating surface, bulk, and coulomb free energies.

Graphene is a two-dimensional material with extremely favorable chemical sensor properties. Conventional nanolithography typically leaves a resist residue on the graphene surface, whose impact on the sensor characteristics has not yet been determined. Here we show that the contamination layer chemically dopes the graphene, enhances carrier scattering, and acts as an absorbent layer that concentrates analyte molecules at the graphene surface, thereby enhancing the sensor response. We demonstrate a cleaning process that veriliably removes the contamination on the device structure and allows the intrinsic chemical responses of the graphene monolayer to be measured. These intrinsic responses are surprisingly small, even upon exposure to strong analytes such as ammonia vapor.

Graphene oxide membranes up to 2000 mu m(2) in size can be synthesized with 90% yield in bulk quantities through a microwave-assisted chemical, method. Membranes are readily visualized on an oxidized silicon substrate, which enables efficient fabrication of electronic devices and sensors. Field effect transistors made of the membrane show ambipolar behavior, and their conductivity is significantly higher than previously reported values.

We report broadband visible photoluminescence from solid graphene oxide, and modifications of the emission spectrum by progressive chemical reduction. The data suggest a gapping of the two-dimensional electronic system by removal of pi-electrons. We discuss possible gapping mechanisms, and propose that a Kekule pattern of bond distortions may account for the observed behavior.