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Vertical graphene (VG) films can be fabricated on the surface of nickel foil from fullerene soot (FS) under microwave plasma irradiation (MPI) in a mixture gas of H2 and Ar at 1200 W for 15 min. The resulting FS-derived VG films mostly consist of few-layer graphene sheets with large domain graphene sizes, high graphitization order, and high purity, as characterized by scanning and transmission electron microscopies, Raman spectroscopy, and X-ray photoelectron spectroscopy. Combined the present and previous results, MPI technique is an effective and versatile approach to synthesize vertically oriented graphene sheets from any carbon-containing sources.

The composites consisting of graphene oxides (GOs) and carbon spheres (CSs), which were hydrothermally derived from the aqueous solution of glucose with average diameter of 200 nm, were mechanically mixed, and the GOs/CSs (GCSs) were thermally treated at high temperatures in the range of 700–900 °C. In the GCS composites, the CSs as spacers located between the GO sheets prevent the aggregation and restacking of graphene sheets. The GCS composites (GO/CS = 1) treated at 800 °C (GCS@800) have the high specific capacitances of 272.8 and 197.5 F g−1 in a three-electrode cell at the current density of 0.2 and 10 A g−1, respectively, in 6 M KOH aqueous solution, and demonstrated high rate capability and good cycling stability. The excellent electrochemical performance of the GCS@800 electrode is attributed to its structure with hierarchical porous structures including overwhelming micropores and a few of macropores. This work provides an effective and simple technique by integrating CSs and graphene sheets into composite structures for high-performance energy storage devices.

This work demonstrates a high-energy-density and flexible supercapacitor as a potential energy source for smart electronics devices. Cathode and anode are fiber-shaped electrodes with manganese oxide (MnO2) being electrochemically inserted into densely interconnected carbon nanotube (CNT) networks as active domains, while carbon fibers (CF) serve as current collectors. The CNT/MnO2 hybrids are built up as a co-axial shell with an optimized thickness of 1.44 μm surrounding CF. Specific volumetric capacitance is found as high as 527 F cm−3 when a 1.0 M Na2SO4 aqueous solution is used as electrolyte; when a solid electrolyte (polyvinyl alcohol and lithium chloride, PVA/LiCl) is used, the specific volumetric capacitance is found as high as 492 F cm−3. These values, to the best of our knowledge, are the highest values of the specific volumetric capacitance among all the MnO2-based fiber-shaped electrodes reported in previous literature. An all-solid-state (PVA/LiCl) symmetric fiber-shaped supercapacitor cell is assembled and a volumetric energy density of 8.14 mWh cm−3 which is high enough for driving a portable LED device, is obtained. Our fiber-shaped supercapacitor cell is safe, flexible, and capable of powering smart electronic devices.

Sol-gel processed niobium oxide (Nb2O5) thin-film was synthesized for a scaffold layer (SL) of methylammonium lead iodide-based perovskite film. Complementary characterizations, including scanning electron microscopy, X-ray diffraction, optical absorption spectroscopy have revealed that the Nb2O5 SL facilitates efficient crystallization of the perovskite film compared to the conventional mesoporous titanium oxide (m-TiO2) SL. Also, photoluminescence spectroscopy revealed the higher electron-extraction capability at the perovskite/Nb2O5 interface than the perovskite/m-TiO2 interface. The present sol-gel processed Nb2O5 SL and the superior optoelectronic properties of the overlying perovskite film suggest a promising avenue for high-performance and cost-effective perovskite solar cells.

Nano-size EVONIK AEROXIDE® P25 titanium dioxide, TiO2, powder was heat-treated at temperatures, 700–900°C, in air. An X-ray diffraction study showed that the P25 powder is composed of approximately 20 and approximately 80 mass% of rutile and anatase phases, respectively. It was also shown that the transformation from anatase to rutile induced by hightemperature heat treatment was almost completed at 750°C, whereas a small amount (less than 3 mass%) of anatase phase was still left even in the powder heat-treated at 900°C. The transformation behaviour was consistent with results obtained by Raman scattering spectroscopy. Raman experiments also indicated that high-temperature heating induced the formation of oxide ion vacancies. Powders were dispersed in methyl orange (MO) aqueous solution, and the bleach rate of MO was measured to evaluate photocatalytic activity under ultraviolet (UV)- and visible-light irradiation. After the heat treatment, the UV-light photocatalytic performance sharply deteriorated. Interestingly, visible-light photocatalytic activity was enhanced by high-temperature heating and reached the highest performance for an 800°C-heated sample, indicating that the P25 powder obtained high visible-light photocatalytic performance after heat treatment. Even after 900°C heat treatment, the photocatalytic performance was higher than that of as-received powder. Enhancement of photocatalytic activities was discussed in relation to visible light absorption and charge carrier transfer., T.I., H.O. and D.H. were supported by a programme, the Strategic Research Foundation at Private Universities, grant no. S1311023, from Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

Graphitization of carbon materials plays an important role their microstructures and conductivity, and then influences their applications. However, the graphitization of hydrothermal carbon spheres (CSs) has not systemically investigated heretofore. The CSs with 60–250 nm in diameter were prepared from aqueous glucose solution by hydrothermal carbonization, and were treated at the high temperatures of 900–2900 °C in Ar atmosphere. The heat-treated CSs have demonstrated that their surface structure, microstructure, porosity, and polygonization strongly depend on the treatment temperatures. These results are supported by scanning and transmission electron microscopes, energy dispersive x-ray spectrometry, Raman, X-ray diffraction, and BET surface area analyses. We also investigated the electrical properties of the heat-treated CSs under compression, and found that the resistivity of the carbon particles is very dependent on their surface, microstructure, density, and polygonization. Therefore, high temperature treatment is an effective method to tailor the structure, morphology, and property of the hydrothermal CSs.

Manganese oxide (MnO2) has long been investigated as a pseudo-capacitive material for fabricating fiber-shaped supercapacitors but its poor electrical conductivity and its brittleness are clear drawbacks. Here we electrochemically insert nanostructured MnO2 domains into continuously interconnected carbon nanotube (CNT) networks, thus imparting both electrical conductivity and mechanical durability to MnO2. In particular, we synthesize a fiber-shaped coaxial electrode with a nickel fiber as the current collector (Ni/CNT/MnO2); the thickness of the CNT/MnO2 hybrid nanostructured shell is approximately 150 μm and the electrode displays specific capacitances of 231 mF cm−1. When assembling symmetric devices featuring Ni/CNT/MnO2 coaxial electrodes as cathode and anode together with a 1.0 M Na2SO4 aqueous solution as electrolyte, we find energy densities of 10.97 μWh cm−1. These values indicate that our hybrid systems have clear potential as wearable energy storage and harvesting devices. Manganese dioxide is a promising material for energy storage applications, but is limited by its brittleness and poor conductivity. Here, manganese dioxide domains are electrochemically deposited onto carbon nanotube networks to produce flexible and conductive hybrid fiber-shaped supercapacitors.

Due to its unique structure and amazing physiochemical properties including high chemical inertness, large specific surface area, and high electric conductivity, graphene, a two-dimensional single sheet of carbon atoms consisting of honeycomb lattices, has attracted great scientific interest in the enormous applications, for example, optical electronics, photovoltaic cells, energy storage, composite materials, filter membranes, and biological engineering, and is regarded as a basic building block for graphitic materials of all other dimensionalities. Recently, another two-dimensional graphitic sheet, vertical graphene (VG), which is typically aligned vertically on a substrate, is attractive for the abovementioned graphene-based applications. The novel vertical orientation and open structures of VGs make it more suitable for sensing biomarkers with high sensitivity and selectivity in complex biological conditions. Until now, VG biosensors have been investigated for detecting diverse biomolecules with or without the modification of metal nanoparticles. More importantly, the plasma technique for the growth and modification of VG is useful but simple tool to optimize the biosensor performance and capabilities. In this chapter, we will simply introduce the synthesis, characteristics, and fundamental properties of VG and carefully discuss the recent studies of VG-based biosensors including electronic and electrochemical biosensors.

Recently, graphene and carbon nanotube (CNT) composites have attracted great interest of scientists and exhibited fascinating properties even better than they could on their own. Here, we have synthesized the graphenated CNTs (g-CNTs), one of graphene–CNT composites, from waste rice husk (RH) by one-step microwave plasma irradiation (MPI) process. The RH-derived g-CNTs were composed of graphene standing on the sidewalls of CNTs, in which the graphene sheets possessed a large amount of sharp edges, which mainly consisted of 2–6 layers, and the CNTs had several tens of micrometers in length and 50–200 in diameter. They offer great promise in the application of electrochemical electrodes due to their special features including high surface area and specific capacitance. The successful MPI technique can be spread to other waste biomass, in which their components are made of cellulose, hemicellulose, and lignin similar to RHs, to fabricate high-added-value nanocarbons including graphene, CNTs, and g-CNTs, which were dependent of experimental pressure.

Helical graphite whiskers (GWs) have been synthesized from fullerene waste soot, which is a byproduct in fullerene production by arc discharge technique, at 2600 °C for 1 h with Ar gas flow at 760 Torr. The as-synthesized GWs consisting of graphite layers with some disclination possess various kinds of morphological structures with loop-like brims and arch-shaped protrusion on their surfaces, as observed by scanning and transmission electron microscopy. The GWs show strong intensity of 2D peak in Raman spectra, which could be attributed to disclination in the whiskers.

Graphene-sheet fiber, a novel structure of graphitic carbon, grew from coffee grounds under the condition of microwave plasma irradiation. The resulting fiber consisted of only few-layer graphene without a hollow structure inside while possessing a large amount of graphene edges and high conductivity. Due to these advantages, graphene-sheet fibers may find applications in electrochemical energy conversion and storage.

Vertically-aligned carbon nanosheets (CNSs), which were fabricated by microwave plasma-enhanced chemical vapor deposition in Ar and CH 4 system, have been annealed at high temperatures in the range of 1200–3000 °C. The morphologies and microstructures of the treated CNSs were analyzed by scanning and transmission electron microscopes, and Raman spectroscopy. High temperature treatment process efficiently removed the amorphous carbon and some defects and improved the graphitization of the CNSs. The graphitized grains increase and the interlayer spacing decreases with increasing heat temperatures. Heat treatment of the CNSs at temperatures from 1500 to 2000 °C was found to achieve the edges consisting of many single-layer graphene sheets. Annealing at temperatures above 2100 °C, the edges of nanosheets consist of 2–5 layer graphene with many zigzag junctions. The mechanism of reconstruction for the edges in the CNSs ascribes possibly to the carbon atom vaporization at high temperatures.

Vertically aligned carbon nanosheets (CNSs) with bi- and trilayer graphene have been achieved on various metal substrates from solid carbon sources by irradiation with H2 and Ar plasma. The resulting graphene structures have fewer layers, bigger sizes, and higher graphitization compared to previous reports obtained from gas sources, as confirmed by scanning and transmission electron microscopes, Raman and X-ray photoelectron spectroscopes. The results suggest that the interaction between the plasma (of H2 and Ar) and carbon sources favors the formation of bigger and thinner nucleation cites in the initial stage and atomic H etching dominates during the whole thinner CNS growth. The vertically aligned graphene film can be directly transferred on as-patterned SiO2/Si to form a heterojunction photovoltaic cell with a power conversion efficiency of 0.9%.

This report describes carbon nanosheets (CNSs) were employed as a catalyst support for loading platinum nanoparticles (Pt NPs) by one-step electrodeposition. The structure, size, and chemical composition of the CNS-supported Pt NPs (Pt/CNSs) were characterized by scanning and transmission electron microscopies, energy dispersive X-ray and X-ray photoelectron spectroscopies. The electrocatalytic performances of the Pt/CNSs for methanol oxidation have been investigated by cycle votammetry and chronoamperometry. These results demonstrated the Pt/CNSs possess high electrocatalytic activity and excellent stability due to high dispersion of Pt NPs on the CNS surface and the special nature properties of CNSs. The Pt/CNSs should be a promising electrocatalyst in direct methanol fuel cells.

We employ a new gas mixture of CH 4 –Ar to fabricate carbon nanosheets by microwave plasma enhanced chemical vapor deposition at the growth temperature of less than 500 °C. The catalyst-free nanosheets possess flower-like structures with a large amount of sharp edges, which consist of a few layers of graphene sheets according to the observation by transmission electron microscopy. These high-quality carbon nanosheets demonstrated a faster electron transfer between the electrolyte and the nanosheet surface, due to their edge defects and graphene structures.

Divalent cation-substituted α-phase tricalcium phosphates (α-Ca3-xMx(PO4)2, where M = Mg, Zn, Sr, Ba) were obtained by heating at 1500 °C for M=Mg (x = 0.03), 1400 °C for the others (x = 0.09), respectively. The resulting products were characterized by XRD, hydration reactivity and hydration-hardening strength. The hydration reactivity of these α-phase phosphates was decreased by the substitutions, regardless of smaller or larger M in ion size than Ca, i.e., the α phase was chemically stabilized.

Oligoacenes are of interest as organic p-type semiconductors for use in electronic devices, but their use as n-type semiconductors is limited. N-Heteroacenes have been investigated as oligoacene-ba...

Solid-phase reaction of cerium and C 60 powders under 600 °C may yield unusual magnetic materials which involve fairly strong dia- and ferro-magnetism at almost similar low temperature range, below 13.5 K. The temperature dependence of the electrical resistivity of this material may indicate that the diamagnetism is due to the superconductivity and there are possible interplays between the superconductivity and the ferromagnetism in this material.

Thin films of hybrid material (ssDNA–SWCNT) prepared by ultrasonic mixing of both materials in water have been examined from the viewpoint of electrical, magnetic and optical properties, and morphological features to probe the possibly induced novel functions due to mutual interactions. Enclosing of DNA molecules inside a SWCNT is confirmed by the image and its motion. The temperature dependence of electrical resistivities is best-fitted to the two-dimensional variable-range-hopping regime. The radial breathing mode of the Raman spectra of the SWCNT exhibits significant modification due to interaction with DNA. The expected change in magnetic susceptibilities is not found in this case.

Laterally dialkylated nematogens containing a short terminal polyoxyethylene chain present a wide nematic range starting from room temperature. The ordering of the oxyethylene (OE) unit has been studied by 13C NMR in the liquid crystalline phase. The values of the order parameters were derived from the transient oscillations observed during variable contact-time cross-polarization experiments. Along the oxyethylene chain, the order parameters decrease monotonically. These order parameter values do not present the usual odd-even effect and are noticeably smaller than those found for terminal alkoxy chains. Entering the nematic phase, the 13C thermal evolution of the field-induced chemical shift in the OE unit is far smaller than the one usually observed for terminal alkyl or alkoxy chains, regardless of their non-negligible order parameters. In addition,no linear correlation between the order parameter and the field-induced chemical shift is observed for the carbons in the OE unit. This is an indication th...

The temperature dependent solid state 15 N CPMAS NMR spectra of 15 N enriched salicylideneaniline derivatives, N-salicylideneaniline (SA). N,N'-bissahcylidene-p-phenylenediamine (BSP) and N.N'-di(2-hydroxy-1-naphthylidene)-p-phenytenediamin (DNP) were measured in order to study possible proton transfer processes in the NHO hydrogen bonds. For DNP a remarkable change of the 15 N chemical shifts of more than 50 ppm was observed between 26 and 388 K by using the CPMAS NMR technique down to cryogenic temperatures. The result clearly indicates very small enthalpy differences among the four tautormers associated with the combination of two possible forms, OH and NH form, of the two NHO hydrogen bonds in a DNP molecule.

An attempt at modifying the electronic conduction mechanism by guest-host charge transfer and thermally excited molecular motion is reported. Ethylenediamine was intercalated into a semiconducting layered material, titanium disulfide, and a significant increase in charge carriers was evidenced by metallic conductivity, Pauli paramagnetism, and conduction electron spin resonance. Rotational motion of the guest molecule was evidenced by the proton spin-lattice relaxation measurement. However, no anomalous behaviors were found on the electronic properties which are attributable to motion-induced modification of the electronic state.

1,6-Diaminopyrene (DAP) is a strong electron donor which can form charge-transfer complexes with many electron acceptors. When the acceptor is TCNQ, a highly conducting crystal comprising segregated-stacks of DAP and TCNQ is obtained. The temperature dependence is semiconducting with anomalously large activation energy for conduction. When the acceptor is p-chloranil (CHL) or 2,5-dibromo-3,6-dichloro-p-benzoquinone (DBDCQ), polymorphic crystals comprising mixed-stacks of DAP and CHL or DBDCQ are obtained. One of the polymorphs, α-form, is not conducting at the initial state, but becomes conducting after a mild heat treatment. It also becomes highly conducting only by fracture of the crystals. The ground state of the low-resistance phase has been found to be mainly neutral, despite its high conductivity.

Structural and electronic properties have been analyzed for stage-4 sodium-hydrogen-graphite intercalation compound (NaHGIC) using 13 C and 1 H NMR. 13 C NMR revealed the existence of charge transfer from the intercalates to graphite. The layer-by-layer charge distribution was estimated to be − 0.029 e per carbon atom for the bounding layers and − 0.005 e for the interior layers. The 1 H NMR spectrum is consistent with the model of intercalate structure where the planar hydride lattice is placed between the sodium cationic layers. The layer structure and the in-plane concentration of hydride ions are similar to those of potassium-hydrogen (KH)GIC. However, the cation concentration is smaller than that in KHGIC, and a more neutralized intercalate lattice thus formed explains the relatively localized electronic property of NaHGIC. 1 H NMR also shows the existence of a motionally narrowed spectral component of 10–15% in relative intensity at room temperature, attributable to molecular hydrogen rapidly rotating in the voids in the intercalate lattice.

The transient photoconductivity of C 70 single crystal excited by 800 ns pulsed N 2 laser pulse was studied. The mobility of positive and negative free charge carriers was determined (≈1cm 2 /Vs) which is found to be similar to that determined for C 60 single crystal. Trapping of free carriers in C 70 was revealed to be much faster than in C 60 leaving for the lifetime of free carriers only 16 ns. Dark charge injection was shown to occur from gold or aluminum electrodes, and excitation in these conditions resulted in delayed generation of the photocurrent within the time domain of microseconds. This phenomenon was shown to be connected with triplet excitons which detrap injected electrons or holes just producing photoenhanced current. Triplet exciton annihilation may follow. Studying the decay of transient photocurrent within hundreds of microseconds time domain has permitted us to characterize the trapping sites as being 0.1 eV deep and having a size of about 25 A. The trapping sites are speculated to be caused by structural imperfections which cause local increase of π-electron density and polarizability. A prominent electrical field effect (of Poole-Frenkel type) was revealed on the thermal detrapping rate that appears to be a rare example of the electrical field effect on the neutral trapping sites.

A combination of 1,6-diaminopyrene and p-chloranil gives two kinds of 1 : 1 charge-transfer complex crystals from a benzene solution. The α-form is triclinic, space group , a = 8.963(1), b = 9.112(2), c = 6.730(1) A, α = 99.59(1), β = 99.65(1), γ = 114.43(1)°, V = 476.0(1) A3, and Z = 1; the β-form is also triclinic, space group , a = 8.123(3), b = 9.708(3), c = 6.791(2) A, α = 110.73(2), β = 108.89(2), γ = 79.11(3)°, V = 472.3(3) A3, and Z = 1. In both crystals, the donors and acceptors are neutral, and stack alternately. The main difference between the α- and β-forms is in the overlapping mode. Both crystals are electrically insulating at the initial states. The α-form single crystal, however, undergoes and irreversible conductivity change upon mild heating (< 380 K) or fracture of the crystal into powder. In both cases, the conductivity change amounts to 106 to 108, and the resultant solids are highly conducting semiconductors. Structural, optical, magnetic, and solid-state NMR studies suggest that the...

Characterization and application of carbon nanosheets (CNSs) grown by microwave plasma enhanced chemical vapor deposition (MPECVD) have been investigated for the electrochemical biosensor. The as-grown CNS films possess a porous structure with a large amount of graphene edges which most of them are less than 2 nm in thickness, as confirmed by scanning and transmission electron microscopes. "Surface-sensitive" probe, Fe(CN)(6)(3-/4-), exhibits that the original CNSs have faster electron transfer than glassy carbon electrode, owing to much more edge plane sites on the original CNS surface. "Oxygen-sensitive" probe, Fe(3+/2+) also confirmed that the oxygen species in the CNS film can improve its electrochemical activity. The modified electrode by MPECVD CNS films has been used to detect NADH for the first time. The CNSs with many graphene edges efficiently catalyse the oxidation of NADH at 0.336 V. The biosensor linearly responds to NADH in the range of 0-500 μM (R=0.99665), the sensitivity of the electrode is 85.8 mA M(-1) or 715 mA M(-1) cm(-2), and the detection limit of NADH is about 0.44 μM (S/N=3). The biosensor also displays excellent stability for NADH detection and good selectivity in the interference from ascorbic acid.

The bare Pt electrode modified directly and simply by carbon nanosheets, which were synthesized by microwave plasma enhanced chemical vapor deposition at relatively low temperature, can be used to simultaneously and effectively detect dopamine, ascorbic acid and uric acid.

Electronic structures of various kinds of alkali metal (Na, K, Rb or Cs)-doped C 60 solids are studied by electrical resistivity and thermoelectric power measurements by using C 60 single crystals prepared from a CS 2 solution as a starting material. For K-or Rb-doped C 60, metallic conducting behaviors in the normal conducting state and relatively sharp superconducting transitions are observed by the electrical resistivity measurements. Nearly linear-temperature dependences with the negative sign are observed in the thermoelectric power measurements at the normal conducting states for K-or Rb-doped C 60. From electron diffusion term of the thermoelectric power, the values of Fermi energy and the density of states at the Fermi energy are estimated by assuming the three-dimensional free electron model, which are in substantial agreement with the results of other experiments and calculations. "Metal–semiconductor transition" is observed in both the electrical resistivity and the thermoelectric power measurements for Na-doped C 60. Existence of metallic phase is confirmed by the thermoelectric power measurement in Cs-doped C 60.

The first observation of a “metallic” conductivity behavior by resistivity measurements is reported for a potassium-doped C60 single crystal. The superconducting transition takes place very sharply with about one degree temperature width, that is, the onset of Tc is 20 K and the resistivity becomes null at 19 K. The details of the doping process are described.

Temperature dependence of resistivity, ρ, of a two-dimensional polymer phase of Na4C60 has been studied from 190 to 300 K. The ρ was 6.9×103 Ω cm at 300 K, which is higher by six orders than those of metallic fullerides. The temperature dependence of ρ shows a semiconducting behavior in this temperature region. This result is different from the previous result derived from ESR which suggests a metallic property above 100 K. The gap energy, Eg, was estimated to be 0.8 eV. This value is close to those of other A4C60 (A:K, Rb and Cs).

The thermoelectric power of K- and Rb-doped C 60 superconductors prepared from single crystals grown from a CS 2 solution is reported. Nearly linear temperature dependences of the thermoelectric power with negative sign are observed above the superconducting transition temperatures for both materials. From the slope of the linear correlation, the ratio of the density of states at the Fermi energy, N Rb (E F )/N K (E F ), is estimated to be 1.5-1.8

High temperature-treated compounds of mixed powders of cerium metal and C 60 solid show fairly strong diamagnetic signal in the zero-field-cooling process and distinct ferromagnetic behavior in the field-cooling path below 13.5K and 15K, respectively. In the resistivity measurement of a compacted and long-term heated pellet of the powder a distinct drop of the resistivity with decreasing temperature is recognized around 20K, which is followed by a steep rise of the resistivity below 14K. These findings indicate an existing competition of superconductivity and ferromagnetism in this compound.

We employed Ar–CH4 to synthesize carbon nanosheets (CNSs), which are two-dimensional carbon nanostructures, by microwave plasma-enhanced chemical vapor deposition at relatively low temperatures and working pressures. The CNSs consist of few-layer graphene nanosheets with 1–3 nm thick sharp edges and possess a large amount of defects, as characterized by scanning and transmission electron microscopies, energy-dispersive X-ray and Raman spectroscopy. Owing to their extraordinary characteristics, the synthesized CNSs can be used to modify the electrodes and exhibit fast electron transfer kinetics in the inner sphere redox system of Fe(CN)6 3-/4- and remarkably active electrocatalytic and biosensing properties.