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Vertically oriented graphene nanosheets are promising electrode materials for electrochemical double-layer capacitors. The external surface area of the nanosheets allows for extremely fast response times compared to porous carbon materials currently used. Furthermore, the high edge density increases the charge storage ability of the material. In this paper Ar+ ions were used to create a larger density of surface defects, which were then characterized by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The results indicate a change in the density of states near the Fermi level with increased defect density, which suggests a corresponding increase in electrochemical capacitance capability.

The growth, capacitance and frequency response of vertically-oriented graphenes grown by radio frequency plasma-enhanced chemical vapor deposition on nickel substrates and used as electrodes in electric double layer capacitors (EDLCs) are presented. The graphenes grown on the grain boundary of substrates show a faster growth rate, but less ordered structure than in the center of the nickel grain. At a few nanometers away from the grain boundaries the graphenes grow vertically at the rate of 70–80 nm per minute. The film height increased linearly with growth time from 700 nm (10 min sample) to 3.1 μm (40 min sample). Raman spectra show that the intensity ratio of the D band to G band gradually decreased with growth time to a value of 0.5, indicating that the crystalline order of the graphene increases with height. The specific capacitance of symmetric, parallel plate EDLC devices fabricated with these films was found to increase in a linear fashion with growth time up to values greater than 120 μF/cm2 at 1 kHz. An impedance phase angle of −45° was reached at 30 kHz. Specific capacitance normalized to growth height suggests that mechanisms other than double layer charge storage on planar surface area were operative.

In situ reduction of graphene oxide (GO) at moderate temperatures within a polymer was observed using differential scanning calorimetry (DSC). Comparison of heats of reduction from DSC data in poly(vinylpyrrolidone), poly(vinyl acetate), and poly(vinylpyrrolidone/vinyl acetate) nanocomposites demonstrates that the polymer chemistry strongly influences the extent of reduction. These results are compared to the time–temperature relationship for GO reduction in air and in dimethylformamide at the same temperatures, determined through changes in the atomic carbon-to-oxygen ratio. GO reduction was independently confirmed by electrical conductivity and optical absorption measurements, as well as Raman spectroscopy. These results show that GO sheets are reduced depending on the time–temperature history and polymer chemistry at the particles’ location. For nanocomposites this can lead to improvement or reduction of desired properties and is thus pertinent to thermal processing of polymer nanocomposites based on f...

The objective of this work was to character- ize and, thereby, achieve a fundamental scientific under- standing at the molecular level of the relationship of the intermolecular forces measured at the nanoscale between an individual nanoparticle and a polymer. In this study, we developed a method to directly characterize and mea- sure the relative strength of the interfacial attractive forces between graphene oxide (GO) nanoparticles and the poly- mer matrix on the nanoscale using atomic force micros- copy techniques to evaluate individual particles. The method was successfully applied to study the interfacial attractive forces in GO-polymer nanocomposites. Two polymers (poly(methyl methacrylate) and poly(vinyl alco- hol)) were studied. The results support that this method is capable of characterizing the interfacial attractive forces directly at the nanoscale. The method can be applied to other nanoparticle-macromolecular systems, allowing the determination of the interaction strength between nanopar- ticles and the macromolecular material. This information paves the way to characterize the relationship between interfacial forces at the nanometer level to a nanocompo- site's performance properties. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3740-3744, 2011

Basic Research Project of National Defence [XMDX2008176]; Key Project Founded by Fujian province, China [20061-10090]

The growth and electrical characteristics of vertically oriented graphene nanosheets grown by radio frequency plasma-enhanced chemical vapor deposition from C2H2 feedstock on nickel substrates and used as electrodes in symmetric electric double layer capacitors (EDLC) are presented. The nanosheets exhibited 2.7 times faster growth rate and much greater specific capacitance for a given growth time than CH4 synthesized films. Raman spectra showed that the intensity ratio of the D band to G band versus temperature initially decreased to a minimum value of 0.45 at a growth temperature of 750 °C, but increased rapidly with further temperature increase (1.15 at 850 °C). The AC specific capacitance at 120 Hz of these EDLC devices increased in a linear fashion with growth temperature, up to 265 μF/cm(2) (2 μm high film, 850 °C with 10 min growth). These devices exhibited ultrafast frequency response: the frequency response at -45° phase angle reached over 20 kHz. Consistent with the increase in D band to G band ratio, the morphology of the films became less vertical, less crystalline, and disordered at substrate temperatures of 800 °C and above. This deterioration in morphology resulted in an increase in graphene surface area and defect density, which, in turn, contributed to the increased capacitance, as well as a slight decrease in frequency response. The low equivalent series resistance varied from 0.07 to 0.08 Ω and was attributed to the significant carbon incorporation into the Ni substrate.

Noncontact mode atomic force microscopy was used to investigate native silk proteins prepared in different ways. Low protein concentrations revealed that single protein molecules exhibit a simple, round shape with apparent diameters of 20–25 nm. Shearing the native protein solutions after extraction from the gland and prior to drying led to a beads-on-a-string assembly at the nanometer scale. Protein concentration had a significant effect on the morphology of the protein assemblies. At higher protein concentrations, shear-induced alignment into nanofibrils was observed, while lower concentrations lead to the formation of much thinner fibrils with a width of about 8 nm.

Tin oxide thin films have been deposited on oxide silicon substrates using a RF magnetron sputtering process with various sputtering power. The crystal structures of the tin oxide thin films were characterized and analyzed by X-ray diffraction. The surface morphology of the films were observed by SEM. The electrochemical properties of the films were also tested by constant current charge and discharge cycle tests. The results of XRD indicate that all the films are crystalline. The results of SEM exhibit that the grain size of surface expands as sputtering power rises.

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For applications of two-dimensional graphene, commercially viable sources are necessary. Exfoliation from bulk, stacked graphite is the most economical way to achieve large quantities of single layer graphene. A number of methods have been developed to achieve exfoliation of graphite, each with advantages and disadvantages. In this review, we describe current exfoliation methods and techniques used to produce single layer materials from graphite precursors.

National 973 Program [2009CB220102]; National Defence [XMDX2008176]; Fujian province [2006H0090]