Hironori Ogata

NMR investigation of the oxyethylene unit ordering in some related dialkoxy laterally substituted nematogens

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...

Mobilities of charge carriers in C60 orthorhombic single crystal

Abstract Time-of-flight technique has been used to measure mobilities of electrons and holes in C60 orthorhombic single crystals at room temperature. Single crystals of C60 grown from the CS2 solution have been characterized as having about 1014cm−3 deep trapping sites for electrons and holes. The mobility for holes (μh) at room temperature is 1.1 ± 0.1 cm2 Vs and that for electrons is found within the same limits. Temperature dependence of μh is revealed to be almost constant from 325 to 250 K. μh starts increasing and below 250 K may be approximated by the law μ h ∼ exp ( ΔE kT ) with ΔE = 0.053 eV. Coincidence of the point of the increase of hole mobility with the phase transition temperature is worthy to be noted.

Charge transport and superconducting transitions in C60 single crystals and thin films doped with rubidium

Superconductivity is confirmed in rubidium-doped C60 samples prepared from single crystals and thin films, by electrical resistivity measurements. Superconducting transition temperatures (Tc) are observed at Tc(onset)=30 K, Tc(offset)=26 K, and Tc(onset)=22 K, Tc(offset)=2.5 K, respectively. The details of the doping conditions are described.

Microwave plasma-induced graphene-sheet fibers from waste coffee grounds

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.

Modification of electronic structure by charge transfer and molecular motion in titanium disulfide-ethylenediamine intercalation compound

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.

Structures and magnetic properties of high-temperature reaction products of cerium metal and C60 solid

Abstract Structures and magnetic properties of high temperature reaction products of Ce metal and C60 solid have been investigated by means of X-ray diffraction and SQUID magnetometory. The X-ray diffraction patterns of relatively low temperature products show that they seem to undergo metal–ion-intercalation to C60 crystals. Unusual behaviors in the temperature dependence of the magnetization of the products have revealed the coexistence or competition of the ferromagnetic and diamagnetic (superconducting) natures occurrence of which depends on the reaction temperatures and times.

NMR study of sodium-hydrogen-graphite ternary intercalation compound

Abstract 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.

Electronic properties of C60 and alkali metal doped C60 thin films or single crystals

Abstract Molecular beam epitaxy technique has been applied to prepare ultra-thin films of C 60 (fullerite) and some optical properties, absorption spectra and nonlinear opitical activities, have been studied. Morphological studies on the sub-mono-molecular layers have been carried out with TEM and STM technique. Electrical conductivities of alkali metal doped C 60 (fulleride) have been measured for single crystals as well as thin films including the detection of their superconductivity.

Fabrication and Electrochemical Characterization of Carbon Nanosheets by Microwave Plasma-Enhanced Chemical Vapor Deposition

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)63-/4- and remarkably active electrocatalytic and biosensing properties.

Growth and Electrochemical Properties of Carbon Nanosheets via Microwave Plasma Enhanced Chemical Vapor Deposition

Various morphologies and microstructures of carbon nanosheets (CNSs) were fabricated using microwave plasma enhanced chemical vapor deposition with different CH4 ratios in Ar gas below 500 oC. With increasing CH4 supplies, the CNSs decrease in flake size, as confirmed by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The CNSs exhibit petal-like structures that consist of graphene nanosheets with a large amount of defects without impurity elements. Extending the growth time, CNSs with smaller crystalline sizes and more defects can be obtained at low CH4 supply and easily peeled from the Cu substrate. The CNSs placed directly on the surface of a glassy carbon electrode demonstrate fast electron transfer kinetics and simultaneously detect dopamine, ascorbic acid and uric acid with high selectivity and sensitivity.