Convenient synthesis of Fe-filled boron nitride nanotubes by SHS method

Fe-filled boron nitride (BN) nanotubes with high purity and good yield were conveniently synthesized by a novel ball-milling and self-propagation high-temperature synthesis (SHS) method at a low temperature (700 °C). The as-prepared product was characterized by XRD, FTIR, SEM, TEM and HRTEM. The results of XRD, FTIR and HRTEM reflect that the product is a hexagonal BN nanotube filled with Fe. The results of SEM and TEM reveal that the Fe-filled BN nanotubes have a diameter of 20-150 nm with the wall-thickness of about 20 nm and the length of more than 5 μm. The possible growth mechanism was also discussed.     

Deformation-driven electrical transport of individual boron nitride nanotubes

In contrast to standard metallic or semiconducting graphitic carbon nanotubes, for years their structural analogs, boron nitride nanotubes, in which alternating boron and nitrogen atoms substitute for carbon atoms in a graphitic network, have been considered to be truly electrically insulating due to a wide band gap of layered BN. Alternatively, here, we show that under in situ elastic bending deformation at room temperature inside a 300 kV high-resolution transmission electron microscope, a normally electrically insulating multiwalled BN nanotube may surprisingly transform to a semiconductor. The semiconducting parameters of bent multiwalled BN nanotubes squeezed between two approaching gold contacts inside the pole piece of the microscope have been retrieved based on the experimentally recorded I-V curves. In addition, the first experimental signs suggestive of piezoelectric behavior in deformed BN nanotubes have been observed.     

The Role of Boron Nitride in Graphite Plasma Arcs

Novel graphitic nanostructures (e.g. nanotubes, graphitic onions, polyhedral particles, hemitoroidal nanotube caps and branched nanotubes) are produced by arcing graphite electrodes, containing hexagonal-BN, in inert atmospheres. The introduction of BN or B inside the graphite anode generates long (≤ 20μm) and well graphitised carbon nanotubes exhibiting boron at their tips. High Resolution Electron Microscopy (HRTEM), Scaning Electron Microscopy (SEM), Electron Energy Loss Spectroscopy (EELS) and X-ray powder diffraction studies reveal the production of B₄C crsytals, in addition to little amounts of BC₃ nanotubes. Mass spectrometry (MS) studies over the generated soots indicate high yields of large fullerenes (e.g. C₇₀, C₇₆, and C₈₄) and thermo-Gravimetric analysis (TGA) of the nanostructures show high oxidation resistance.     

Purification of boron nitride multiwalled nanotubes

Purification of arc-discharge grown multiwalled boron nitride nanotubes (BN MWNTs) was possible using a simple solubilization and filtration method. Using the common method of arc-discharge with h-BN/Ni/B packed molybdenum tube and a water cooled copper cathode, results in a mixture of hexagonal boron nitride, metal catalyst and boron nitride nanotubes. We show that a simple purification based on the use of surfactants that provide sufficient solubilization for solution filtering of the other materials results in highly purified BN MWNTs. The purified samples were characterized by transmission electron microscopy and scanning tunneling spectroscopy and microscopy. We observed in the purified BN MWNTs square and triangular tube ends, characteristic for this type of nanotube with no metal observed at the tips. Tunneling spectroscopy measurements showed an averaged band gap of approximately 5 eV with the band gap values independent of tube chirality and diameters.     

Double-walled boron nitride nanotubes grown by floating catalyst chemical vapor deposition

One-dimensional nanostructures exhibit quantum confinement which leads to unique electronic properties, making them attractive as the active elements for nanoscale electronic devices. Boron nitride nanotubes are of particular interest since, unlike carbon nanotubes, all chiralities are semiconducting. Here, we report a synthesis based on the use of low pressures of the molecular precursor borazine in conjunction with a floating nickelocene catalyst that resulted in the formation of double-walled boron nitride nanotubes. As has been shown for carbon nanotube production, the floating catalyst chemical vapor deposition method has the potential for creating high quality boron nitride nanostructures with high production volumes.     

An effective precursor for growth of bubble-chain boron nitride nanotubes

Large amounts of bubble-chain boron nitride nanotubes were synthesised by annealing an effective precursor. The porous precursor was produced by self-propagation high-temperature synthesis method using Mg, B₂O₃, amorphous B and Fe₂O₃ as the starting materials, which played an important role in synthesis of BN nanotubes in large quantities. Samples were characterised by SEM, TEM, HRTEM, X-ray powder diffraction and Raman and Fourier transform infrared spectroscopy. The as-synthesised BN nanotubes revealed periodical bubble-chain structures, having diameters of range 20–200?nm?and an average length of more than 5?µm. The effects of temperature, time and the possible mechanism of the growth of the BN nanotubes were also discussed.     

Catalytic growth of bamboo-like boron nitride nanotubes using self-propagation high temperature synthesized porous precursor

The high-pure bamboo-like boron nitride (BN) nanotubes with high yield were synthesized via an effective chemical vapor deposition method by annealing porous precursor under NH₃ atmosphere at 1150 °C. The porous precursor was readily prepared by self-propagation high temperature synthesis (SHS) method. The as-synthesized BN nanotubes were characterized by SEM, TEM, HRTEM, XRD, Raman and FTIR spectroscopy. The results indicate these nanotubes have bamboo-like structures with an average diameter of about 90 nm and length of more than 10 μm. Nanotube content is estimated as approximately 90 wt.% according to the statistical analyses by SEM and TEM. Moreover, the reaction mechanism for the as-synthesized BN nanotubes is proposed.     

Electronic structures and three-dimensional effects of boron-doped carbon nanotubes

Abstract

We study boron-doped carbon nanotubes by first-principles methods based on the density functional theory. To discuss the possibility of superconductivity, we calculate the electronic band structure and the density of states (DOS) of boron-doped (10,0) nanotubes by changing the boron density. It is found that the Fermi level density of states D(?_F) increases upon lowering the boron density. This can be understood in terms of the rigid band picture where the one-dimensional van Hove singularity lies at the edge of the valence band in the DOS of the pristine nanotube. The effect of three-dimensionality is also considered by performing the calculations for bundled (10,0) nanotubes and boron-doped double-walled carbon nanotubes (10,0)@(19,0). From the calculation of the bundled nanotubes, it is found that interwall dispersion is sufficiently large to broaden the peaks of the van Hove singularity in the DOS. Thus, to achieve the high D(?_F) using the bundle of nanotubes with single chirality, we should take into account the distance from each nanotube. In the case of double-walled carbon nanotubes, we find that the holes introduced to the inner tube by boron doping spread also on the outer tube, while the band structure of each tube remains almost unchanged.     

C-BN patterned single-walled nanotubes synthesized by laser vaporization

We report on the synthesis of C-BN single-walled nanotubes made of BN nanodomains embedded into a graphene layer. The synthesis process consists of vaporizing, by a continuous CO2 laser, a target made of carbon and boron mixed with a Co/Ni catalyst under N2 atmosphere. High-resolution transmission electron microscopy (HRTEM) and nanoelectron energy loss spectroscopy (nanoEELS) provide direct evidence that boron and nitrogen co-segregate with respect to carbon and form nanodomains within the hexagonal lattice of the graphene layer in a sequential manner. A growth model is proposed to account for the observed C-BN self-organization and to explain how kinetics and local energetics at intermediate states can tailor ultimate single layer BN-C heterojunctions.     

脉冲偏压下沉积的立方氮化硼膜的断面结构研究

采用自行研制的磁增强活性反应离子镀系统 ,在脉冲偏压条件下成功地合成了高品质立方氮化硼 (c BN)薄膜。用傅立叶变换红外谱 (FTIR)分析沉积膜的相结构 ,用透射电镜 (TEM)及高分辨率透射电镜 (HRTEM)分析膜的断面结构。FTIR结果表明 :c BN的纯度强烈地受基片负偏压的影响 ,当基片负偏压为 15 5V ,c BN膜的纯度高达 90 %以上。TEM及HRTEM对膜的断面结构分析表明 ,在膜与基片的界面处存在很薄的非晶氮化硼和六方氮化硼 (h BN)层 ,h BN(0 0 0 2 )晶面垂直于基片表面 ,在界面层之上生长着单相c BN层     

Electro-thermo-torsional buckling of an embedded armchair DWBNNT using nonlocal shear deformable shell model

Electro-thermo-torsional buckling response of a double-walled boron nitride nanotube (DWBNNT) has been investigated based on nonlocal elasticity and piezoelasticity theories. The effects of surrounding elastic medium such as the spring constant of the Winkler-type and the shear constant of the Pasternak-type are taken into account. The van der Waals (vdW) forces are considered between inner and outer layers of nanotube. According to the relationship between the piezoelectric coefficient of armchair boron nitride nanotubes (BNNTs) and stresses, the first order shear deformation theory (FSDT) is used. Energy method and Hamilton’s principle are employed to obtain coupled differential equations containing displacements, rotations and electric potential terms. The detailed parameter study is conducted to investigate the effects of nonlocal parameter, elastic foundation modulus, temperature change, piezoelectric and dielectric constants on the critical torsional buckling load. Results indicate that the critical buckling load decreases when piezoelectric effect is considered.     

The influence of the stacking orientation of C and BN stripes in the structure, energetics, and electronic properties of BC2N nanotubes

Carbon and boron nitride nanotubes present significant differences in their electronics. However, they have isoelectronic bonds and very similar geometrical structures that allow BCN nanotubes to be synthesized. These BCN nanotubes present properties that can vary according to their relative number of B, C, and N atoms, and their atomic distribution on the nanotube surface. Here we employ first-principles density functional theory to study BCN nanotubes with BC(2)N stoichiometry. These nanotubes are composed of pure BN and C stripes which are stacked (i) in parallel, (ii) perpendicularly, and (iii) forming helicoidal patterns along the nanotube axes. We found that the different strain energies of the curved C and BN arcs in the nanotubes with parallelly aligned stripes can lead to geometries that deviate significantly from the usual circular shape. A sinusoidal shape was predicted for a BC(2)N nanotube with a helicoidal arrangement of the C and BN stripes due to differences in the C-B and C-N bonds parallel to the tube axis. It was shown that the phase segregation is energetically favoured. Such structural preference and the relative stability of the BC(2)N nanotubes can be explained in terms of the ratio between the total number of bonds and the number of C-B and C-N bonds in the nanotubes. Finally, we found that one type of BC(2)N nanotube with helicoidal C and BN stripes, although having a zigzag structure, exhibits a metallic character.     

Dynamics of carbon nanotube growth from fullerenes

The growth of double-walled carbon nanotubes from peapods was studied. The transformation was monitored by the decrease of fullerene Raman lines, the growth of inner tube Raman lines, and the development of X-ray diffraction patterns. A visual check of the growth process by HRTEM provided additional information. From the difference in time constants for the bleaching of fullerene Raman lines and for the growth of nanotube Raman lines, the existence of an intermediate phase was concluded that was eventually observed in X-ray diffraction and HRTEM. Time constants for the growth of large diameter inner tubes were up to a factor two larger than for small diameter inner tubes. The results fully support the fullerene coalescence growth model triggered by Stone-Wales transformations.     

Elastic Vibration Behaviors Oof Carbon Nanotubes Based on Micropolar Mechanics

The concept of the micropolar theory is employed to investigate vibration behaviors of carbon nanotubes. The constitutive relation has been deduced from the two-dimensional analysis of the microstructure of the carbon nanotube. Van der Waals interactions are simulated by a weak spring model. Hamilton's principle is employed to obtain dynamics equations of the multi-walled carbon nanotube. Numerical examples for both single-walled and double-walled carbon nanotubes are presented and the significant difference in vibration behaviors between them has been distinguished. Numerical results show that fundamental frequencies for the cantilever single-walled carbon nanotube decreases with increase of the aspect ratio of them, and the fundamental frequencies of the double-walled carbon nanotube are lower than those of the single-walled carbon nanotube with the same inner diameter and length. The first four natural frequencies for the double-walled carbon are coaxial.     

Atomic nanotube welders: boron interstitials triggering connections in double-walled carbon nanotubes

Here we demonstrate that the incorporation of boron (B) atoms between double-walled carbon nanotubes (DWNTs) during thermal annealing (1400-1600 degrees C) results in covalent nanotube "Y" junctions, DWNT coalescence, and the formation of flattened multiwalled carbon nanotubes (MWNTs). These processes occur via the merging of adjacent tubes, which is triggered by B interstitial atoms. We observe that B atom interstitials between DWNTs are responsible for the rapid establishment of covalent connections between neighboring tubes (polymerization), thereby resulting in the fast annealing of the carbon cylinders with B atoms embedded in the newly created carbon nanotube network. Once B is in the lattice, tube faceting (polygonization) starts to occur, and the electronic properties are expected to change dramatically. Therefore, B atoms indeed act as atomic nanotube fusers (or welders), and this process could now be used in assembling novel electronic nanotube devices, nanotube networks, carbon nanofoams and heterojunctions exhibiting p-type electronic properties.     

Synthesis of multiwall boron nitride nanotubes dependent on crystallographic structure of boron

Synthesis and growth of multiwall boron nitride nanotubes (BNNTs) under the B and ZrO₂ seed system in the milling–annealing process were investigated. BNNTs were synthesized by annealing a mechanically activated boron powder under nitrogen environment. We explored the aspects of the mechanical activation energy transferred to milled crystalline boron powder producing structural disorder and borothermal reaction of the ZrO₂ seed particles on the synthesis of BNNTs during annealing. Under these circumstances, the chemical reaction of amorphous boron coated on the seed nanoparticles with nitrogen synthesizing amorphous BN could be enhanced. It was found that amorphous BN was crystallized to the layer structure and then grown to multiwall BNNTs during annealing. Especially, bamboo-type multiwall BNNTs were mostly produced and grown to the tail-side of the nanotube not to the round head-side. Open gaps with ∼0.3 nm of the bamboo side walls of BNNTs were also observed. Based on these understandings, it might be possible to produce bamboo-type multiwall BNNTs by optimization of the structure and shape of boron coat on the seed nanoparticles.     

Multi-Walled Nanotubes: Commensurate-Incommensurate Phase Transition and NEMS Applications

Interaction of non-rigid walls of double-walled carbon nanotubes is studied within the Frenkel-Kontorova model. It reveals a clearly defined commensurate-incommensurate phase transition. Parameter which determines this phase is calculated for a set of double-walled nanotubes with non-chiral commensurate walls using ab initio interwall interaction energies and elastic properties. Possibility of formation of incommensurability defects in the commensurate phase is considered. The length of the defects and energy of their formation are calculated. Principal scheme of strain nanosensor based on the commensurate-incommensurate phase transition in double-walled nanotube is proposed.     

Synthesis of peapods using substrate-grown SWNTs and DWNTs: an enabling step toward peapod devices

We report the successful synthesis of nanoscale peapods from single-walled and double-walled nanotubes grown by chemical vapor deposition (CVD) on substrates with windows etched into free-standing silicon nitride membranes. CVD-grown nanotubes were oxidized in air, then filled with C(60) molecules from the vapor phase. Observed variation in nanotube oxidation and C(60) packing with nanotube diameter agreed with theoretical expectations. Windowed samples provide several important advantages for property measurements of peapods and other nanomaterials. Individual nanostructures can be followed through processing steps, and a single nanostructure can be inspected by high-resolution TEM and subsequently contacted with nanoscale electrodes using electron beam lithography.     

Syntheses and properties of B-C-N and BN nanostructures

The current status of research on boron-carbon-nitrogen (B-C-N) and boron nitride (BN) nanotubes is presented. The latest achievements in syntheses, analyses and property measurements of these nanoscale tubular architectures are reviewed. The characteristic features of B-C-N and BN nanotubes, compared with conventional C nanotubes, are paid special attention. In particular, the latest breakthroughs in the chemical vapour deposition synthesis of BN nanotubes and an insight into their unique structures are highlighted. A wide range of potential applications is also envisaged, based on the recent progress, which includes pioneering results in BN nanocable fabrication, gas adsorption, electron transport and field emission measurements.     

Boron nitride-based electrocatalysts for HER,OER, and ORR: A mini-review

A reliable and efficient solution to the current energy crisis and its associated environmental issues is provided by fuel cells, metal–air batteries and overall water splitting. The heart reactions for these technologies are oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Different supporters such as graphene, carbon nanotube, and graphitic carbon nitride have been used to avoid agglomeration of active materials and provide maximum active surface for these reactions. Among all the supporters, boron nitride (BN) gains extensive research attention due to its analogue with graphene and excellent stability with good oxidation and chemical inertness. In this mini-review, the well-known strategies (exfoliation, annealing, and CVD) used in the synthesis of BN with different morphologies for HER, OER and ORR applications have been briefly debated and summarized. The comparative analysis determines that the performance and stability of state-of-the-art electrocatalysts can be further boosted if they are deposited on BN. It is revealed that BN-based catalysts for HER, OER and ORR are rarely studied yet especially with non-noble transition metals, and this research direction should be studied deeply in future for practical applications.