Using molecular level modification to tune the conductivity of graphene papers

Graphene's excellent electrical conductivity benefits from its highly conjugated structure. Therefore, the manipulation of graphene's electronic and mechanical properties should be realized by controlled destruction of its in-sheet conjugation. Here, we r

Temperature variations at nano-scale level in phase transformed nanocrystalline NiTi shape memory alloys adjacent to graphene layers

The detection and control of the temperature variation at the nano-scale level of thermo-mechanical materials during a compression process have been challenging issues. In this paper, an empirical method is proposed to predict the temperature at the nano-scale level during the solid-state phase transition phenomenon in NiTi shape memory alloys. Isothermal data was used as a reference to determine the temperature change at different loading rates. The temperature of the phase transformed zone underneath the tip increased by _3 to 40 _C as the loading rate increased. The temperature approached a constant with further increase in indentation depth. A few layers of graphene were used to enhance the cooling process at different loading rates. Due to the presence of graphene layers the temperature beneath the tip decreased by a further _3 to 10 _C depending on the loading rate. Compared with highly polished NiTi, deeper indentation depths were also observed during the solidstate phase transition, especially at the rate dependent zones. Larger superelastic deformations confirmed that the latent heat transfer through the deposited graphene layers allowed a larger phase transition volume and, therefore, more stress relaxation and penetration depth.

Mild and cost-effective synthesis of iron fluoride-graphene nanocomposites for high-rate Li-ion battery cathodes

Exploring high performance cathode materials is essential to realize the adoption of Li-ion batteries for application in electric vehicles and hybrid electric vehicles. FeF3, as a typical iron-based fluoride, has been attracting considerable interest due to both the high electromotive force value of 2.7 V and the high theoretical capacity of 237 mA h g_1 (1e_ transfer). In this study, we report a facile lowtemperature solution phase approach for synthesis of uniform iron fluoride nanocrystals on reduced graphene sheets stably suspended in ethanol solution. The resulting hybrid of iron fluoride nanocrystals and graphene sheets showed high specific capacity and high rate performance for iron fluoride type cathode materials. High stable specific capacity of about 210 mA h g_1 at a current density of 0.2 C was achieved, which is much higher than that of LiFePO4 cathode material. Notably, these iron fluoride/ nanocomposite cathode materials demonstrated superior rate capability, with discharge capacities of 176, 145 and 113 mA h g_1 at 1, 2 and 5 C, respectively.

Tuning radical species in graphene oxide in aqueous solution by photoirradiation

Graphene oxide (GO) possesses unusual electronic and mechanical properties, including the ability to stabilize graphene radicals (GRs). However, controlled generation of GRs remains a challenge for applications requiring large-scale production. In this study, we demonstrate controlled production of GRs by UVB irradiation of GO solutions. Electron paramagnetic resonance spectroscopy of GO solutions revealed a dose-dependent exponential growth in radical production as a function of UVB exposure time. The GRs were air-stable over a long period, both in the solution state and in freeze-dried powders, suggesting they are graphene-based phenalenyl-like radicals. The redox activity of GRs was demonstrated by their ability to oxidize the chromophore 3,5,3?,5?- tetramethylbenzidine, with oxidation capacity of GO increasing with GR content.

Facile synthesis of graphene oxide hybrids bridged by copper ions for increased conductivity

In this article, we report a facile method for preparing graphene oxide (GO) hybrid materials consisting of copper ions (Cu2+) complexed with GO, where Cu2+ acted as bridges connecting GO sheets. The method of film formation is based on cross-linking GO using Cu2+ followed by filtration onto nanoporous supports. This binding can be rationalized due to the chemical interaction between the functional groups on GO and the metal ion. We observed that there was a decrease in charge transfer resistance through electrochemical study. It suggests that the presence of metal ions in GO films could introduce new energy levels along the electron transport pathway and open up possible conduction channels. We also found that the hybrid graphene film assembled with Cu2+ dramatically decreases resistance through flash light reduction.

Acceleration effect of reduced graphene oxide on photoinduced synthesis of silver nanoparticles

The photoinduced growth reaction of silver nanoparticles was accelerated by reduced graphene oxide (RGO) produced from graphene oxide (GO) during the light irradiation process in aqueous solution. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy demonstrated that RGO was generated in the photoinduced process. The acceleration effect of RGO was investigated through monitoring the extinction spectra of silver nanoparticles during the synthesis process. Moreover, transmission electron microscopy (TEM) was employed to characterize the evolution of morphologies of silver nanoparticles at different irradiation times to demonstrate the effect of RGO. The results indicate that RGO accelerates the photoinduced synthesis of silver nanoparticles. It is proposed that the acceleration effect of RGO on the photoinduced reaction is attributed to the particular property of high electronic conductivity

Variable incidence angle subwavelength grating SPR graphene biosensor

This paper investigates the sensitivity enhancement of a variable incidence angle subwavelength grating based multilayer surface plasmon resonance biosensor (SPRB). In the proposed design, a periodic array of subwavelength grating is integrated on top of a layer of graphene sheet in the multilayer SPR biosensor. The performance of the biosensor is investigated through monitoring the biomolecular interactions of cDNA-ssDNA interactions on its surface. The sensitivity improvement is indicated by the shift of the resonance peak angle.