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Abstract: Boron nitride (BN) nanotubes and nanohorns with various tip structures were synthesized by arc-melting LaB6 powders. Atomic structure models and formation mechanism for BN nanotubes and nanohorns were proposed from high-resolution electron microscopy (HREM), energy dispersive X-ray spectroscopy (EDX), molecular mechanics calculations (MM2) and thermodynamic calculation. The present work indicates that lanthanum would be a key catalytic material to produce the BN nanostructures. [Copyright &y& Elsevier]

Abstract: Bamboo-type boron nitride (BN) nanotubes with cup-stacked structures were produced by annealing of Fe4N and boron particles at 1000°C for 5h in nitrogen atmosphere. The iron nitride particles were reduced to α-Fe. Atomic structure models and the formation mechanism were proposed from the results of high-resolution electron microscopy (HREM), image simulations and molecular mechanics calculations. The nanotube structures would be stabilized by stacking of BN cup-layers. [Copyright &y& Elsevier]

Abstract: Boron nitride (BN) nanohorns were synthesized by arc-melting YB6 powders. Method, and atomic structure models for BN nanohorns encaging Y@B36N36 were proposed from high-resolution electron microscopy. The molecular mechanics calculation indicated that BN clusters with metal atoms would be stabilized by being encaged in double-walled BN nanohorns. [Copyright &y& Elsevier]

Abstract: Boron nitride (BN) nanotubes were prepared as mixtures of α-Fe2O3, B and carbon powders, followed by annealing at 1100 °C for 2 h on alumina boats in a furnace under nitrogen atmosphere. BN nanotubes with cup-stacked structures were observed by high-resolution electron microscopy, and molecular mechanics calculation showed that the nanotube structures would be stabilized by stacking of BN cup-layers. [Copyright &y& Elsevier]

Abstract: Boron nitride (BN) nanohorns with various tip angles were synthesized by an arc-melting method, and atomic structure models for BN nanohorns were proposed from high-resolution electron microscopy. Stability and electronic structures of the BN nanohorns were investigated by molecular orbital/mechanics calculations, which indicated that multi-walled BN nanohorns would be stabilized by stacking of BN nanohorns. The energy gaps of the BN nanohorns were calculated to be 0.20∼0.85 eV, which are lower compared to those of BN clusters and nanotubes. [Copyright &y& Elsevier]

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. BN nanotubes encapsulating BN clusters and a yttrium nanowire were also found. This article 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. [ABSTRACT FROM AUTHOR]

Abstract: Boron nitride (BN) nanohorns were synthesized by an arc-melting method, and atomic structure models for BN nanohorns with tetragonal BN rings were proposed from high-resolution electron microscopy. Stability and electronic structures of the BN nanohorns were investigated by molecular orbital/mechanics calculations. The calculation showed that multiwalled BN nanohorns would be stabilized by stacking of BN nanohorns. The energy gap of BN nanohorn was calculated to be 0.8eV, which is lower compared to those of BN clusters and nanotubes. [Copyright &y& Elsevier]

Boron nitride (BN) nanocage clusters (BnNn: n=24–60) were synthesized by arc-melting method and detected by mass spectrometry and high-resolution electron microscopy. Endohedral boron nitride clusters Y@BnNn would also be formed. The BN clusters consist of 4-, 6- and 8-membered BN rings satisfying the isolated tetragonal rule, which was optimized by molecular orbital calculations. The electronic structure showed that bandgap energies increase with increase of cluster size. [Copyright &y& Elsevier]

Boron nitride (BN) nanotubes with zigzag- and armchair-type structures were investigated by high-resolution electron microscopy, image processing, image simulation and molecular mechanics calculations. Chiralities of BN nanotubes were directly determined from high-resolution images, and structure models were 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. [Copyright &y& Elsevier]

Hexagonal networks of boron nitride (BN) nanotubes were investigated by high-resolution electron microscopy (HREM) and image simulation. From HREM images, lattice planes of {002} and hexagonal rings of a BN nanotube were confirmed. Asymmetrical layer arrangements were found, and a structure model for double-walled BN nanotube with an armchair-type structure has been proposed. [Copyright &y& Elsevier]

High-resolution electron microscopy, mass spectrometry and molecular mechanics/orbital calculations of the boron nitride-based clusters showed the formation of B36N36 and Y@B36N36. Image simulations of these clusters confirmed the proposed structure model. [Copyright &y& Elsevier]

B12@B12@B60 and B12@(B12)12 giant clusters consisting of B12-based icosahedral clusters in B105Al2.6Cu1.8 and B56Y crystals were directly observed by high-resolution electron microscopy, image calculation and crystallographic image processing. Doping atom positions such as Al, Cu, and Y were also detected in the high-resolution images. The present work indicates that the cluster arrangements with light element of boron could be detected by using the crystallographic image processing technique. [Copyright &y& Elsevier]

Boron nitride (BN) nanotubes were synthesized by an arc-melting method from boride-based powders in N2/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. [Copyright &y& Elsevier]

Arrangements of B84 and B156 clusters consisting of B12-based icosahedral clusters in B105Al2.6Cu1.8 and B56Y crystals were directly observed by high-resolution electron microscopy and crystallographic image processing. Doping atom positions such as Al, Cu, and Y were also detected in the high-resolution images. The present work indicates that the cluster arrangements with light element of boron could be detected by using the crystallographic image processing technique. [Copyright &y& Elsevier]

Nanoparticles of AlB10, TiN and VN encapsulated by boron nitride (BN) layers were synthesized by an arc-melting method in a N2/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. [Copyright &y& Elsevier]

Disordering of both yttrium and boron atoms in YB56 was observed, in three dimensions, from difference images of high-resolution electron microscopy (HREM) and simulated images from an X-ray determined structural model. Averaged HREM images recorded using a slow-scan charge-coupled device camera from thin regions (less than 5 nm) along the [100], [110] and [111] directions of the YB56 were compared with calculated images based on the X ray data. A residual index RHREM was used for image analysis to determine the crystal thickness and defocus value of the observed images. Based on the experimental conditions which minimized the RHREM values, difference images between observed and simulated images were calculated. These difference images observed along the three directions of the YB56 showed the atomic disorder, which are yttrium positions and boron clusters around the yttrium atoms. This approach is useful for the evaluation of disordered atomic positions in the crystal. [ABSTRACT FROM AUTHOR]

Abstract: Boron nitride (BN) nanotubes were synthesized by annealing an iron thin film evaporated on boron pellets at 1000 °C in nitrogen gas atmosphere. The growth mechanism and atomic structures of the BN nanotubes were investigated by high-resolution electron microscopy. Diameters of BN nanotubes are in the range of 10–20 nm, and the nanotubes have a zigzag-type structure. [Copyright &y& Elsevier]

Abstract: Boron nitride (BN) cages were synthesized by annealing Fe4N and B powders at 1000 °C for 1 h in nitrogen gas atmosphere. To remove non-BN clusters such as metal catalyst particles, purification of BN cages was carried out by acid treatment and centrifugation. Large amounts of BN cages were observed by high-resolution electron microscopy and energy-dispersive X-ray spectroscopy, and the cages showed photoluminescence peak at ∼3.8 eV. [Copyright &y& Elsevier]

Boron nitride (BN) nanotubes were investigated by high-resolution electron microscopy (HREM) and image processing. From the HREM image, a BN nanotube encapsulating yttrium nanowire was confirmed by comparing calculated diffraction and a nanostructure model. The present work indicated that yttrium elements could be confined in BN nanotube with large energy gap. [Copyright &y& Elsevier]

Abstract: Boron nitride nanotubes with 100–150nm in diameter were synthesized by annealing a mixture of iron oxide and boron powders at 1373K in nitrogen atmosphere. By adding carbon powders to the mixture, boron nitride nanotubes grew into distinctive structures, which are cup-stacked and bamboo-like structure. Carbon nanotubes and nanowires with 100nm and 200–300nm in diameter were also synthesized by annealing a mixture of iron oxide and carbon powders at 1273K in nitrogen atmosphere. A transmission electron microscope observation showed that boron nitride nanotubes with the cup-stacked and bamboo-like structure did not support metallic iron particles, while the ordinary boron nitride nanotubes, carbon nanotubes and nanowires supported metallic iron particles at their edge. Reaction process between iron oxide and boron or carbon was studied by using thermogravimetry/differential thermal analysis. Considering the observed morphology and analysis results, chemical reactions for the production of these boron nitride and carbon nanomaterials (nanotubes and nanowires) were proposed. Validity of the proposed reactions was investigated thermodynamically. Growth mechanism of the nanomaterials was also discussed. [Copyright &y& Elsevier]