成田 一人

Boron nitride (BN) nanocage clusters (BnNn: n = 12similar to60), endohedral BN clusters Y@BnNn, BN nanotubes and BN nanohorns were synthesized by an arc-melting method, and characterized by mass spectrometry and high-resolution electron microscopy. The BN clusters consisted of 4-, 6-, Band 10-membered BN rings satisfying the isolated tetragonal rule, which was optimized by molecular orbital calculations. Total energy calculation showed that some elements stabilize and expand the B36N36 structure. Bandgap energies of the B36N36 clusters were found to be reduced by introducing a metal atom inside the cluster, which indicates controllability of the energy gap: Chiralities of BN nanotubes with zigzag- and armchair-type structures were directly determined from high-resolution images, and structure models are proposed. Total energies of BN nanotubes with a zigzag-type structure were lower than those of armchair-type structure, and these results agreed well with the experimental data of disordered tube structure. BN nanotubes encapsulating BN clusters and a yttrium nanowire were also found. In addition, BN nanohorns with tetragonal BN rings were synthesized and proposed, and multi-walled BN nanohorns would be stabilized by stacking of BN nanohoms. Possibility of hydrogen gas storage in BN clusters was also investigated by molecular orbital calculations, which indicated possibility of hydrogen storage of similar to5wt. %. The present work indicates that the new BN nanocage fullerene materials with various atomic structures and properties can be produced, and a guideline for designing the BN fullerene materials is summarized.

Boron nitride (BN) nanocage clusters (BnNn: n = 12-60), endohedral BN clusters Y@BnNn and BN nanotubes were synthesized by an arc-melting method, and characterized by mass spectrometry and high-resolution electron microscopy. The BN clusters consisted of 4-, 6-, 8-, and 10-membered BN rings satisfying the isolated tetragonal rule, which was optimized by molecular orbital calculations. Total energy calculation showed that some elements stabilize and expand the B36N36 structure. Bandgap energies of the B36N36 clusters were found to be reduced by introducing a metal atom inside the cluster, which indicates controllability of the energy gap. Chiralities of BN nanotubes with zigzag- and armchair-type structures were directly determined from high-resolution images, and structure models are proposed. Total energies of BN nanotubes with a zigzag-type structure were lower than those of armchair-type structure, and these results agreed well with the experimental data of disordered tube structure.

Boron nitride (BN) nanocage clusters of B28N28 were synthesized, and detected by laser desorption time-of-flight mass spectrometry. The B28N28 clusters consisted of 4- and 6-membered BN rings satisfying the isolated tetragonal rule, which was optimized by molecular orbital calculations. The electronic structure showed a bandgap energy of 5.2 eV. (C) 2004 Elsevier Ltd. All rights reserved.

Boron nitride (BN) nanotubes were synthesized by an arc-melting method from boride-based powders in N-2/Ar mixture gas, and various structures were confirmed by high-resolution electron microscopy and energy dispersive X-ray spectroscopy. NbB2,YB6 and YB6/Ni could be good catalysts to produce BN nanotubes and bundled BN nanotubes by the arc-melting method. (C) 2003 Elsevier Science B.V. All rights reserved.

Boron nitride (BN) nanocage clusters of B24N24 were synthesized and detected by laser desorption time-of-flight mass spectrometry. The B24N24 clusters consisted of 4-, 6- and 8-membered BN rings satisfying the isolated tetragonal rule, which was optimized by molecular orbital calculations. The electronic structure showed a bandgap energy of 4.9 eV, which is smaller than that of B36N36 cluster. (C) 2003 Elsevier B.V. All rights reserved.

Hexagonal zigzag network of boron nitride (BN) nanotubes was investigated by high-resolution electron microscopy (HREM) and image processing. From the HREM image, lattice planes of {002} and hexagonal rings of BN nanotube were confirmed by comparing image simulation and nanostructure models. The present work indicated that arrangement of hexagonal rings of BN nanotubes could be confirmed by combination of HREM image analysis and simulation. (C) 2003 Elsevier B.V. All rights reserved.

Boron nitride (BN) fullerene nanomaterials were synthesized by an arc-melting method from Al/B, TiB2, VB2, Ga/B, YB, YB6/Ni, NbB2 powder in N-2/Ar mixture gas, and various structures were confirmed by high-resolution electron microscopy. From comparing of formation enthalpy with nitrogen and boron, tendency of catalysis metal for BN nanotube was characterized, which is a useful guideline for synthesis of BN fullerene nanomaterials. (C) 2002 Elsevier Science B.V. All rights reserved.

Conditions of H-2 gas storage in B36N36 and C-60 clusters, which were considered as a cap structure of boron nitride and carbon nanotubes, were predicted by first-principle single-point energy calculations. As a result of the calculations, H-2 molecules would be introduced from hexagonal rings of the cage structure. BN fullerene materials store H-2 molecules easier than carbon fullerene materials, and its stability for high temperature is expected to be good. (C) 2002 Elsevier Science B.V. All rights reserved.

The possibility of H-2 gas storage in fullerene-like materials such as carbon clusters and boron nitride clusters was investigated by molecular dynamics calculations. First principle single point energy calculation was also carried out for C-60 and B36N36 clusters with changing point of H-2 molecule to compare the behavior of H-2 molecules at the tetragonal, pentagonal and hexagonal rings. Molecular dynamics calculations showed that a H-2 molecule remains stable in a C-60 cage at 298 K and 0.1 MPa. It is confirmed that pressures over 5 MPa are needed to store H-2 molecules in the C-60 cage. As a result of single point energy calculations, H-2 molecules enter from hexagonal rings of fullerene-like materials. BN fullerene materials can store H-2 molecules easier than carbon fullerene materials, and has good high temperature stability. (C) 2002 Elsevier Science B.V. All rights reserved.

Nanoparticles of AlB10, TiN and VN encapsulated by boron nitride (BN) layers were synthesized by an arc-melting method in a N-2/Ar gas mixture from boron/Al powder compacts, TiB2 and VB2, respectively. From high-resolution electron microscopy observations, formation mechanisms of BN nanocapsules were proposed, and BN tube-like structures were also produced. Magnetization of BN nanocapsules with TiN nanoparticles showed a spin-glass-like behavior. The present work indicates that Al, Ti and V could be a good catalyst to produce BN nanocapsules, nanocages and nanotubes by the arc melting method. (C) 2002 Elsevier Science B.V All rights reserved.

Endohedral fullerenes Si@C-74 were produced by direct current and radio-frequency hybrid are-discharge. Atomic structure analysis and structural optimization of the Si@C-74 were carried out by high-resolution electron microscopy, image simulation, molecular mechanics and ab initio molecular orbital calculations. Total steric energy of the Si@C-74 was the lowest in the present calculation of C-60-C-76 clusters. The energy gap of the Si@C-74 was calculated to be 0.098 eV, and the heat of formation per carbon atom is almost the same as that of the C-60 Cluster. (C) 2002 Elsevier Science B.V. All rights reserved.

La@B36N36 endohedral metallofullerenes were synthesized for the first time, which was observed by high-resolution electron microscopy, and a structure model was proposed. Image simulations of the La@B36N36 clusters also showed the possible existence of a La atom inside the BN clusters. Atomic structures, structural stabilities and electronic structures of La@B36N36, Fe@B36N36 and B36N36 clusters were investigated by molecular mechanics and molecular orbital calculations, which showed that the B36N36 clusters are expanded by introducing doping atoms and the energy gap of B36N36 is reduced by introducing La and Fe atoms inside the B36N36 cluster. (C) 2002 Elsevier Science B.V. All rights reserved.

Boron nitride nanotubes were synthesized by an arc-inciting method from YB6 powder in N-2/Ar mixture gas, and various structures were confirmed by high-resolution electron microscopy and energy dispersive X-ray spectroscopy. (C) 2002 Elsevier Science Ltd. All rights reserved.

Various boron nitride (BN) and carbon (C) nanocage fullerene materials (clusters, metallofullerenes, onion, nanotubes and nanocapsules) were synthesized by arc-melting, electron-beam irradiation, chemical reaction, and self-organization. Atomic structures and structural stability of these materials were investigated by high-resolution electron microscopy, energy dispersive spectroscopy, electron energy-loss spectroscopy, molecular mechanics, molecular dynamics and molecular orbital calculations. Photoluminescence, magnetic and electronic properties of these fullerene materials were also investigated. The present work indicates that: the new BN and C nanocage fullerene materials with various atomic structures and properties can be produced by various synthesis methods, and a guideline for designing the BN and C fullerene materials is summarized. (C) 2001 Elsevier Science Ltd. All rights reserved.

A carbon onion with a tetrahedral structure was produced by electron-beam irradiation of amorphous carbon, and structure models of C-84 and C-276 were optimized by molecular mechanics and semi-empirical molecular orbital calculation.