Tuning the Electrical Properties of Graphene via Nitrogen Plasma-Assisted Chemical Modification.

The control in electrical properties of graphene is essentially required in order to realize graphenebased nanoelectronics. In this study, N-doped graphene was successfully obtained via nitrogen plasma treatment. Graphene was synthesized on copper foil using thermal chemical vapor deposition. After N2 plasma treatment, the G-band of the graphene was blueshifted and the intensity ratio of 2D- to G-bands decreased with increasing the plasma power. Pyrrolic-N bonding configuration induced by N2 plasma treatment was studied by X-ray photoelectron spectroscopy. Remarkably, electrical characterization including Hall measurement and I-V characteristics of the N-doped graphene exhibit semiconducting behavior as well as the n-type doping effect.

Immobilization of carbon nanotubes on functionalized graphene film grown by chemical vapor deposition and characterization of the hybrid material.

We report the surface functionalization of graphene films grown by chemical vapor deposition and fabrication of a hybrid material combining multi-walled carbon nanotubes and graphene (CNT-G). Amine-terminated self-assembled monolayers were prepared on graphene by the UV-modification of oxidized groups introduced onto the film surface. Amine-termination led to effective interaction with functionalized CNTs to assemble a CNT-G hybrid through covalent bonding. Characterization clearly showed no defects of the graphene film after the immobilization reaction with CNT. In addition, the hybrid graphene material revealed a distinctive CNT-G structure and p-n type electrical properties. The introduction of functional groups on the graphene film surface and fabrication of CNT-G hybrids with the present technique could provide an efficient, novel route to device fabrication.

Synthesis of graphene and carbon nanotubes hybrid nanostructures and their electrical properties.

The gapless semimetallic nature of graphene-based nanoelectronics is a major hurdle for the advancement of graphene-based field-effect transistors. Here graphene-carbon nanotubes hybrid nanostructures (Gr-CNTs HNSs) were formed by synthesizing single-walled carbon nanotubes (SWCNTs) with a bandgap on monolayer graphene by thermal chemical vapor deposition. We systematically established optimum conditions for the synthesis of Gr-CNTs HNSs by adjusting catalytic layer formation. The structural features of Gr-CNTs HNSs were investigated by scanning electron icroscopy and Raman spectroscopy. The surface morphologies and chemical states of the catlytic films used to optimize Gr-CNTs HNSs synthesis were explored by atomic force microscopy and X-ray photoelectron spectroscopy. In this process, graphene played a role as a barrier to prevent Fe nanoparticles from interdiffusing into Al2O3 layer. Based on these studies, we determined the catalytic structure (Fe/Graphene/Al2O3/SiO2) optimal for growing high-density SWCNTs on monolayer graphene. Electrical transport measurements revealed that Gr-CNTs HNSs exhibited p-type semiconducting behavior with combined properties of graphene and CNTs.

Synthesis of bandgap-controlled semiconducting single-walled carbon nanotubes.

Bandgap-controlled semiconducting single-walled carbon nanotubes (s-SWNTs) were synthesized using a uniquely designed catalytic layer (Al(2)O(3)/Fe/Al(2)O(3)) and conventional thermal chemical vapor deposition. Homogeneously sized Fe catalytic nanoparticles were prepared on the Al(2)O(3) layer and their sizes were controlled by simply modulating the annealing time via heat-driven diffusion and subsequent evaporation of Fe at 800 degrees C. Transmission electron microscopy and Raman spectroscopy revealed that the synthesized SWNTs diameter was manipulated from 1.4 to 0.8 nm with an extremely narrow diameter distribution below 0.1 nm as the annealing time is increased. As a result, the bandgap of semiconducting SWNTs was successfully controlled, ranging from 0.53 to 0.83 eV, with a sufficiently narrow energy distribution, which can be applied to field-effect transistors based on SWNTs.

Combustion characteristics of spent catalyst and paper sludge in an internally circulating fluidized-bed combustor.

Combustion of spent vacuum residue hydrodesulfurization catalyst and incineration of paper sludge were carried out in thermo-gravimetric analyzer and an internally circulating fluidized-bed (ICFB) reactor. From the thermo-gravimetric analyzer-differential thermo-gravimetric curves, the pre-exponential factors and activation energies are determined at the divided temperature regions, and the thermo-gravimetric analysis patterns can be predicted by the kinetic equations. The effects of bed temperature, gas velocity in the draft tube and annulus, solid circulation rate, and waste feed rate on combustion efficiency of the wastes have been determined in an ICFB from the experiments and the model studies. The ICFB combustor exhibits uniform temperature distribution along the bed height with high combustion efficiency (>90%). The combustion efficiency increases with increasing reaction temperature, gas velocity in the annulus region, and solid circulation rate and decreases with increasing waste feed rate and gas velocity in the draft tube. The simulated data from the kinetic equation and the hydrodynamic models predict the experimental data reasonably well.