Showing papers by "Ryo Kitaura published in 2012"

Dimerization-Initiated Preferential Formation of Coronene-Based Graphene Nanoribbons in Carbon Nanotubes

Abstract: We have investigated the growth mechanism of coronene-derived graphene nanoribbons (GNRs) using two different precursors: coronene and a dimer form of coronene, so-called dicoronylene (C48H20). For both of the precursors, the formation of nanoribbon-like materials inside carbon nanotubes (CNTs) was confirmed by transmission electron microscope observations. Experimental and theoretical Raman analysis reveals that the samples also encapsulated dicoronylene and linearly condensed other coronene oligomers, which can be regarded as analogues to GNRs. Interestingly, it was found that the present doping condition of coronene yields dicoronylene prior to encapsulation due to the thermal dimerization of coronene. These results indicate that the dimerization before the encapsulation drives the preferential formation of the coronene-based GNRs within CNTs.

Rock-Salt-Type Crystal of Thermally Contracted C60 with Encapsulated Lithium Cation†

Abstract: Rock solid: fullerene-encapsulated Li(+) (Li(+)@C(60)) is an alkaline cation owing to the spherical shape and positive charge. Li(+)@C(60) crystallizes as a rock-salt-type crystal in the presence of PF(6)(-). The orientations of C(60) and PF(6)(-) (orange) are perfectly ordered below 370 K, and Li(+) (purple) hops within the cage. At temperatures below 100 K two Li(+) units are localized at two polar positions within each C(60) .

Synthesis and transformation of linear adamantane assemblies inside carbon nanotubes.

Abstract: We report the assembly and thermal transformation of linear diamondoid assemblies inside carbon nanotubes. Our calculations and observations indicate that these molecules undergo selective reactions within the narrow confining space of a carbon nanotube. Upon vacuum annealing of adamantane molecules encapsulated in a carbon nanotube, we observe a sharp Raman feature at 1857 cm–1, which we interpret as a stretching mode of carbon chains formed by thermal conversion of adamantane inside a carbon nanotube. Introduction of pure hydrogen during thermal annealing, however, suppresses the formation of carbon chains and seems to keep adamantane intact.

Topological difference in 2D layers steers the formation of rigid and flexible 3D supramolecular isomers: impact on the adsorption properties.

Abstract: Starting with the same precursors, pyridine-2,3-dicarboxylate (pyrdc) and 4,4′-bipyridyl (bipy), two 3D porous coordination polymers, {[Cu(bipy)0.5(pyrdc)]·3H2O} (1) and {[Cu(bipy)0.5(pyrdc)]·0.5bipy·3H2O} (2), have been synthesized by changing the solvent system from MeOH/H2O to EtOH/H2O. Single-crystal structure analysis revealed that 1 and 2 are supramolecular isomers with 3D pillared-layer structures having 1D channel systems. Isomer 1 has a flexible structure and shows gated adsorption behavior, while framework 2 has a rigid backbone and exhibits the adsorption properties of typical microporous materials.

Fabrication and Characterization of Graphene/Hexagonal Boron Nitride Hybrid Sheets

Abstract: The synthesis of graphene and hexagonal boron nitride (hBN) hybrid sheets has been achieved using a two-step chemical vapor deposition (CVD) process. Individual grains of single-layer graphene are grown from methane, and hBN is, then, synthesized from ammonia borane on the same copper (Cu) foil. Optical absorption and Raman measurements reveal that the hBN is formed on the bare surface of Cu foil and the graphene grains play a crucial role as an inactive protective layer of Cu foil for the ammonia borane CVD. Furthermore, the hBN growth is found to be initiated preferentially by the edge of graphene grains.

Electronic structure of Eu atomic wires encapsulated inside single-wall carbon nanotubes

Abstract: X-ray absorption (resonant) photoelectron spectroscopy has been employed to investigate electronic structure of Eu atomic wires encapsulated in single-wall carbon nanotubes (SWCNTs). The measurements reveal that there is a substantial electron transfer of $+$1.79 $\ifmmode\pm\else\textpm\fi{}$ 0.11 from a Eu atom to the surrounding SWCNT. The shape of the observed Fermi edge is different from that of a three-dimensional metal, suggesting that electrons in this one-dimensional system form a Tomonaga-Luttinger liquid.

Carbon nanotube manufacturing method

Abstract: Carbon nanotubes (CNTs) having a desired diameter are selectively produced by reacting a carbon source with a cyclic compound in which multiple aromatic rings are continuously bonded. The reaction is preferably performed by supplying a gaseous carbon source under reduced pressure and heating. The cyclic compound in which multiple aromatic rings are continuously bonded is preferably a cyclic compound in which bivalent aromatic hydrocarbon groups are continuously bonded, or a modified cycloparaphenylene compound in which a cycloparaphenylene compound or at least one phenylene group of the cycloparaphenylene compound is substituted with a condensed cyclic group such as a naphthylene group.

Controllable chemical vapor deposition synthesis of single-wall carbon nanotubes using mist flow method

Abstract: The influences of synthesis parameters on the mean diameter and diameter distribution of as-grown single-wall carbon nanotubes (SWCNTs) with chemical vapor deposition (CVD) using the mist flow method have been investigated in detail with Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). We found that CVD reaction temperature and flow rate play an essential role in controlling the mean diameter and the quality of as-grown SWCNTs. Furthermore, we found that the carbon supply kinetics can be a dominant factor to determine the diameter of as-grown SWCNTs in the present mist flow method. Under a different combination of various parameters, the mean diameter of SWCNTs can be varied from 0.9 nm to 1.5 nm controllably.

Preparation and Observation of an Atomic Layer of Gold Formed on the Surface of Graphene

Abstract: Freestanding clean graphene is prepared using graphene samples grown by chemical vapor deposition and direct transfer onto a SiN grid followed by hydrogen plasma treatment. High-resolution transmission electron microscopy has shown that the Au atoms deposited on the graphene possess a unique layer structure with a square arrangement of Au atoms. We found that the Au nanostructure vaporizes under mild electron beam irradiation conditions, which is specific to the unique thin layer structure.

SynthesisandTransformationofLinear Adamantane Assemblies inside Carbon

Abstract: We report the assembly and thermal transformation of linear diamondoid assemblies inside carbon nanotubes. Our calculations and observations indicate that these molecules undergo selective reactions within the narrow confining space of a carbon nanotube. Upon vacuum annealing of adamantane molecules encapsulated in a carbon nanotube, we observe a sharp Raman feature at 1857 cm � 1 , which we interpret as a stretching mode of carbon chains

Carbon Nanotubes Encapsulating Atoms and Molecules

Abstract: Carbon nanotube possesses one-dimensional tubular structure whose diameter typically ranges from 0.4 to 5 nm. Recently, significant research efforts have been devoted to encapsulate various atoms and molecules into inner space of carbon nanotubes to create novel hybrid one-dimensional materials. In this paper, we review recent studies on carbon nanotubes encapsulating atoms and molecules, where the following topics are discussed in detail : formation of metal atomic wires in carbon nanotubes, structure and dynamics of the atomic wires, chirality control of carbon nanotubes based on fusion reaction in carbon nanotubes and extraction of materials from carbon nanotubes.