A Rhombic Dodecahedral Honeycomb Structure with Cation Vacancy Ordering in a γ-Ga2O3 Crystal

The crystal structure of a γ-Ga2O3 layer grown epitaxially on an MgO substrate by a vapor phase transport method was investigated by transmission electron microscopy, electron diffraction, and scanning transmission electron microscopy with aberration correctors. Some forbidden reflections were excited in electron diffraction patterns by double reflection from the vicinity of the substrate interface. Phase boundaries are observed in atomic column images using high-angle annular dark field images. A structure model is proposed to explain the experimental results. Cation vacancy ordering is introduced in the structure model to distort the γ-Ga2O3 crystal lattice along one axis and reduce the lattice mismatch with the substrate. Some grains are formed and alter the directions to reduce the distortion for the other axis. The grains are stacked with {110} phase boundaries and form a rhombic dodecahedral honeycomb. The rhombic dodecahedral honeycomb structure model with cation vacancy ordering is stabilized by the lattice mismatch between the γ-Ga2O3 crystal and the MgO substrate, and it disappears at a depth of 170 nm from the interface

Open nanotubes of insulating boron nitride

Here we report on large arrays of exlusively open-ended multi-walled insulating boron nitride (BN) nanotubes synthesized through heating of carbon (C) nanotubes with metal oxides (CuO, MoO3, or PbO) and boron oxide (B2O3) in a flow of nitrogen. The BN tubes were assembled in bundles several micrometers long. The thermal and chemical stability of the product was found to be superior to conventional C nanotubes, which opens new prospects for intra-tube chemistry at high temperatures, e.g., metal cluster encapsulation and/or entire filling of insulating BN nanotube with conductive metal.</p

Nanotubes of boron nitride filled with molybdenum clusters

Carbon nanotubes are known to be metallic or semiconducting, depending on their helicity and diameter. However, boron nitride (BN) nanotubes are the only nanotubular product known to date that are predicted to have stable insulating properties that are independent of their atomic structure and morphology. Thus, the BN tube has attracted prime attention as an advanced nanoinsulating shield for all types of encapsulated conducting material, i.e., metal wires, clusters, etc. However, so far there have been no successes in controlled one-dimensional filling of BN nanotubes with conductive material. We report the first experimental results on the synthesis, high-resolution transmission electron microscopy, energy dispersion X-ray analysis, and electron energy loss spectroscopy of BN nanotubes that are filled with Mo clusters over their entire length. This was accomplished by means of two-step thermochemical treatment of chemically vapor-deposited C nanotubes with B 2O 3, CuO, and MoO 3 oxides in a flowing N 2 atmosphere. The first examples of BN nanotubes filled with molybdenum clusters are reported and the formation of the first nanocable (∼10 nm in length), consisting of a conductive metal core and an insulating BN nanotubular shield is demonstrated.</p

In situ electrical measurements and manipulation of B/N-doped C nanotubes in a high-resolution transmission electron microscope

B/N-doped multiwalled C nanotubes were electrically probed by means of a tungsten needle attached to a piezo-driven stage of a high-resolution transmission electron microscope holder. Two-terminal transport measurements were performed in a 'W needle-nanotube-ground' circuit. The I-V curves were recorded in situ while viewing the nanotubes in the imaging mode of the microscope. This allows us to trace nanotube array morphological changes under applied voltage (up to 50 V). Specific manipulation with nanotube assemblies was found to be possible under applied electrical field: attachment of a tiny nanotube bundle to the W needle and extraction of a given nanotube fragment from an entangled complex bunch were achieved. The electrically-probed B/N-doped C nanotubes exhibited alternating B-rich and C-rich B-C-N domains within tubular layers, as revealed by elemental mapping during energy-filtered TEM (Omega filter). At room temperature the nanostructures displayed resistivity (ρ) of ∼ 1.8 × 10-5 Ωm and linear I-V curves. The key role of a given contact between the probing needle and a nanotube during electrical measurements was particularly verified.</p

Effective synthesis of surface-modified boron nitride nanotubes and related nanostructures and their hydrogen uptake

The present study is focused on the synthesis of boron nitride nanotubes (BNNTs) with an entirely modified surface structure. We succeeded in the BNNT surface modification by using highly reactive SO2 gas generated in-situ during the tube synthesis. The obtained BNNTs have a high surface area, which is significantly larger than that of standard well-structured BNNT. Therefore, the synthesized nanomaterial is advantageous for the gas adsorption and could be envisaged as a prospective hydrogen-storage material. Herein we report on the preliminary results of the hydrogen accumulation experimental runs