Boron Nitride Nanotube, Nanocable and Nanocone
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Boron Nitride Nanotube, Nanocable and Nanocone Dmitri Golberg, Yoshio Bando*, Laure Bourgeois1, Renzhi Ma, Kazuhiko Ogawa, Keiji Kurashima, Tadao Sato Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, JAPAN 1 Present address: School of Physics and Materials Engineering, PO Box 69M, Monash University, Victoria 3800, AUSTRALIA *corresponding author. E-mail: [email protected] ABSTRACT Boron nitride nanotubes, nanocones and nanocables were prepared and their atomic structures were identified by using a 300 kV field emission transmission electron microscope equipped with an electron energy loss spectrometer and energy dispersion X-ray detector. Multiwalled BN nanotubes and nanocones were synthesized by reacting C nanotube templates and boron oxide under nitrogen atmosphere at 1723-2023 K. Additions of metal oxide promoters, e.g. MoO3, CuO, and PbO, significantly improved BN-rich nanotube yield at the expense of B-C-N nanotubes. It was shown that BN nanotubes had preferential “zigzag” chirality and exhibited either hexagonal or rhombohedral stacking between shells. An efficient synthetic route for bulk quantities of BN tube production was also developed, where a B-N-O precursor was used during a CVD process. Nanocones of BN were mostly found to have 240o disclinations which ensure the presence of B-N bonds only. One case was observed of a cone constituted of 300o disclination implying that structures may contain line defects of non B-N bonds. The first synthesis of insulating BN nanocables was carried out, where BN nanotubes were entirely filled with Invar Fe-Ni nanorods. The filled nanotube diameters ranged between 30 to 300 nm, whereas the length of filling reached several microns.
INTRODUCTION BN nanostructures, e.g. nanotubes [1-6], nanocones [7] and nanocables [8,9] are unique products displaying high-oxidation resistance, thermal stability [10], and thermal conductivity. These nanostructures are usually considered to be the structural analogs of those in graphite [1113], though the atomic structures in BN remain not properly investigated as compared to C, which have been intensively studied for a decade [11-13]. Determination of the nanomaterial atomic structure presumes the knowledge of its morphology variations, capping features, shell chirality, wall stacking order, structure of kinks and other defects. Without this knowledge it is hard to expect smart practical applications of BN nanomaterials in the near future, since their structural and electronic properties may be sensitive to the above-mentioned parameters. For instance, there have been a few intriguing experimental facts on atomic structure difference in BN nanotubes as compared to their C counterparts. It has been shown that BN tube chirality is directly related to the tip-end morphology, that is for commonly observed flat BN tube caps zigzag shell assembly is energetically preferable (the tube axis is parallel to the [10 1 0] graphitic sheet orientation) [14]. Recently the present autho
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