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Inspired by rich physics and functionalities of graphenes, scientists have taken an intensive interest in two-dimensional (2D) crystals of h-BN (analogue of graphite, so-called “white” graphite). Recent calculations have predicted the exciting potentials of BN nanoribbons in spintronics due to tunable magnetic and electrical properties; however no experimental evidence has been provided since fabrication of such ribbons remains a challenge. Here, we show that few- and single-layered BN nanoribbons, mostly terminated with zigzag edges, can be produced under unwrapping multiwalled BN nanotubes through plasma etching. The interesting stepwise unwrapping and intermediate states were observed and analyzed. Opposed to insulating primal tubes, the nanoribbons become semiconducting due to doping-like conducting edge states and vacancy defects, as revealed by structural analyses and ab initio simulations. This study paves the way for BN nanoribbon production and usage as functional semiconductors with a wide range of applications in optoelectronics and spintronics. [ABSTRACT FROM AUTHOR]

An effective method was proposed to remove obstinate boron nitride phase impurities in boron nitride nanotubes (BNNTs). The method is based on strong interactions between BNNTs and a conjugated polymer wrapping them and significant weight and size difference between BNNTs and impurities. The as-grown samples and purified samples were compared through detailed characterization, using scanning electron microscopy, transmission electron microscopy, and Raman and Fourier transformed infrared spectroscopy. The results reveal that impurities are effectively removed and resultant BNNTs possess perfect crystallization. [ABSTRACT FROM AUTHOR]

The fine regulation of catalysts by the atomic-level removal of inactive atoms can promote the active site exposure for performance enhancement, whereas suffering from the difficulty in controllably removing atoms using current micro/nano-scale material fabrication technologies. Here, we developed a surface atom knockout method to promote the active site exposure in an alloy catalyst. Taking Cu3Pd alloy as an example, it refers to assemble a battery using Cu3Pd and Zn as cathode and anode, the charge process of which proceeds at about 1.1 V, equal to the theoretical potential difference between Cu2+/Cu and Zn2+/Zn, suggesting the electricity-driven dissolution of Cu atoms. The precise knockout of Cu atoms is confirmed by the linear relationship between the amount of the removed Cu atoms and the battery cumulative specific capacity, which is attributed to the inherent atom-electron-capacity correspondence. We observed the surface atom knockout process at different stages and studied the evolution of the chemical environment. The alloy catalyst achieves a higher current density for oxygen reduction reaction compared to the original alloy and Pt/C. This work provides an atomic fabrication method for material synthesis and regulation toward the wide applications in catalysis, energy, and others. [ABSTRACT FROM AUTHOR]

Boron nitride nanohorns (BNNHs) are synthesized in large scale. Their morphology and structure were investigated by scanning electron microscopy and transmission electron microscopy. The hollow conical structure and particular aggregation behavior are revealed. Cathodoluminescence measurement is performed and ultraviolet light emission is observed, which indicates the potential applications of BNNHs in optical devices. [ABSTRACT FROM AUTHOR]

Substantial effort has been devoted to endowing flexible and wearable supercapacitors with desirable functions and solving urgent concerns regarding their practical application, particularly materials selection, air permeability, self-healability, shape memory, integration, and modularization. This gives rise to challenges with regard to both suitable materials and device fabrication. This review highlights the current state-of-the-art of these supercapacitors pertinent to materials, fabrication strategies, and performance. Challenges and solutions are also discussed to further improve their practicality. The aim of this review is to make a timely summary of this emerging field and discuss future opportunities and challenges. [ABSTRACT FROM AUTHOR]

The article discusses the process by which boron nitride nanotubes (BNNTs) are dispersed into aqueous media and how individual BNNTs are isolated through the application of a method of peptide wrapping and sonication procedures. The strong pi-pi interactions between BNNTs and peptides are exploited using fluorescence or Fourier transformed infrared spectroscopies. Opportunities for functionalizing and expanding the future applications of BNNTs are offered by the pathway.

The article reports that proteins can be immobilized on boron nitride nanotubes (BNNTs). It suggests that there is a natural affinity of proteins to BNNTs--they can be immobilized on BNNT directly, without using an additional coupling reagent. It also reports that the effect of protein immobilization on BNNTs was studied using high-resolution transmission electron microscopy and energy dispersion spectroscopy. It argues that protein immobilization may be due to carboxylation of BNNT-bound amino groups or prominent tube/protein electrostatic interactions. However, it suggests the use of noncovalently functionalized BNNTs for effective immobilization of proteins.

Presents a correction to the article “Phonon Characteristics and Cathodolumininescence of Boron Nitride Nanotubes,” published in the 2005 issue of the “Applied Physics Letters.”

Layered hydroxides of (Y1−xEux)2(OH)5NO3·nH2O (x= 0−1) have been hydrothermally synthesized under the optimized conditions of 120 °C and pH ∼7.0. Eu incorporation yields steadily smaller particles, elongation of the well-developed hexagon platelets, and linearly expanded abplanes of the layered structure. The interlayer distance (c/2), closely related to the hydration number n, is inversely proportional to the Eu content. The systematically changing photoluminescence behaviors allow to conclude that a lower hydration shifts the Eu3+coordination from C4vto C1symmetries and that the C1-site Eu3+is significantly associated with the 595 nm 5D0→7F1and the 615 nm 5D0→7F2transitions while the C4v-site Eu3+with the 589 nm 5D0→7F1and the 698 nm 5D0→7F4transitions. The hydroxides convert to cubic (Y1−xEux)2O3at temperatures ≥400 °C while retaining the original morphologies. The best luminescence was observed for the oxides at x= 0.05 for the 613-nm red emission, and significant quenching of luminescence occurred at x> 0.10. Red shift of the charge-transfer excitation band was observed to be due to the elongated Eu−O bond arising from lattice expansion. The asymmetry factor of luminescence, I(5D0→7F2)/I(5D0→7F1), exhibits a sharp increase from ∼11.4 at x= 0.5 to ∼23 at x= 1.0, which has been ascribed to the splitting of C1symmetry from distorted S6sites. [ABSTRACT FROM AUTHOR]

We have carried out an isotope study on the band gap and radiative transition spectra of boron nitride nanotubes (BNNTs) using both experimental and theoretical approaches. The direct band gap of BNNTs was determined at 5.38 eV, independent of the nanotube size and isotope substitution, by cathodoluminescences (CL) spectra. At lower energies, several radiative transitions were observed, and an isotope effect was revealed. In particular, we confirmed that the rich CL spectra between 3.0 and 4.2 eV reflect a phonon−electron coupling mechanism, which is characterized by a radiative transition at 4.09 eV. The frequency red shift and peak broadening due to isotopic effect have been observed. Our Fourier transform infrared spectra and density functional theory calculations suggest that those radiative transitions in BNNTs could be generated by a replacement of some nitrogen atoms with oxygen. [ABSTRACT FROM AUTHOR]

Through the use of commercial graphite powders as the carbon sources, a variety of interesting tubular carbon nano- and microstructures, such as networked carbon nanotubes, aligned carbon microtubes with hexagonal cross-sections, aligned tapered carbon tubes, and hollow carbon microhorns, have been successfully synthesized. As-grown tubular carbon structures were characterized using scanning electron microscopy, transmission electron microscopy, and X-ray energy-dispersive spectroscopy. An in situ template mechanism was proposed to explain the possible growth process. The vibrational properties of the synthesized tubular carbon structures were also studied by Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Closed-shell BO2− and BO− anions are proposed as high-efficiency luminescence centres in boron–nitrogen systems, which makes the anions localized and leads to a radiation transition. [ABSTRACT FROM AUTHOR]

Bending modulus of exfoliation-made single-crystalline hexagonal boron nitride nanosheets (BNNSs) with thicknesses of 25-300 nm and sizes of 1.2-3.0 um were measured using three-point bending tests in an atomic force microscope. BNNSs suspended on an SiO2 trench were clamped by a metal film via microfabrication based on electron beam lithography. Calculated by the plate theory of a doubly clamped plate under a concentrated load, the bending modulus of BNNSs was found to increase with the decrease of sheet thickness and approach the theoretical C33 value of a hexagonal BN single crystal in thinner sheets (thickness<50 nm). The thickness-dependent bending modulus was suggested to be due to the layer distribution of stacking faults which were also thought to be responsible for the layer-by-layer BNNS exfoliation. [ABSTRACT FROM AUTHOR]

Herein the recent experiments performed by the authors on fabricated multi-walled BN nanotubes and monoatomic BN graphene-like nanosheets are reviewed. The results are presented in several sections, namely: (i) method for high-yield synthesis of thin, defect-free BN nanotubes of only a few-layers, with external diameters below 10 nm; (ii) verification of BN nanotube piezoelectrical behavior and its electrically-induced thermal decomposition under combined resistive heating and electrical charging in a transmission electron microscope; (iii) the first direct measurements of the true tensile strength and Young's modulus of BN nanotubes, using newly developed nanotensile tests inside an electron microscope; the measured values were found to be ∼30 GPa and ∼900 GPa, respectively; and (iv) diverse kinetic processes taking place within the prepared monoatomic BN sheets (so-called 'white graphenes') affiliated with intensive knock-on B and N atom displacements under high energy electron beam irradiation in an aberration-corrected medium-voltage high-resolution transmission electron microscope. [ABSTRACT FROM AUTHOR]

Individual multiwalled boron nitride nanotubes of different diameters (40−100 nm) were bent inside a 300 kV high-resolution transmission electron microscope (TEM) using a new fully integrated TEM−atomic force microscope (AFM) piezodriven holder under continuous recording of force−piezodisplacement curves. The tubes were gently compressed in situ (i.e., inside the electron microscope) between a piezomovable aluminum wire and a silicon cantilever. Typically, bending stress values ranging from ∼100 to ∼260 MPa, and corresponding to elastic moduli of 0.5−0.6 TPa, were estimated. Tube gross failures were absent up to very large bending angles (in excess of 115°). Extending the bending angles beyond 30−40° resulted in the elastic deformation of BN nanotubes, which proceeded through the propagation of consecutive momentary kinks. These had the effect of accumulating a bending curvature rather then uniformly curl the tube under the compression load. These kinks were found to be entirely reversible on reloading with no (or marginal) traces of residual plastic deformation. [ABSTRACT FROM AUTHOR]

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−Vcurves. In addition, the first experimental signs suggestive of piezoelectric behavior in deformed BN nanotubes have been observed. [ABSTRACT FROM AUTHOR]

Ammonium tetrafluoroborate, a cheap and commonly used chemical, was successfully utilized in this study to synthesize BN-coated MgF2nanowires and collapsed BN nanotubes, although previous investigations have indicated that the compound cannot be used as a chemical vapour deposition (CVD) reaction precursor of amorphous or crystalline BN. Our study reveals that when MgCl2is used as a promoter a crystalline BN phase can be obtained on a large scale. The MgCl2also controls the product morphology, resulting in collapsed BN-coated MgF2nanowires at the first stage of CVD. The detailed morphology of the composite nanowires also depends on the reaction temperature. Increase in temperature stimulates the nanowire formation. The MgF2inclusions can be fully removed via a simple high-temperature evaporation procedure, forming collapsed BN nanotubes of high purity and yield. [ABSTRACT FROM AUTHOR]

Due to fast decomposition of Mg3N2 in the presence of water in the atmosphere (Mg3N2 + 6H2O → 3Mg(OH)2 + 2NH3), the synthesis of single-crystalline Mg3N2 nanowires has been a challenge. Here, we demonstrate that carbon nanotubes may serve as nanoreactors for a simple thermal reaction process resulting in the first fabrication of high-quality, large-yield, single-crystalline Mg3N2 nanowires. The Mg3N2 nanowires are homogeneously sheathed over their entire lengths with very thin graphitic carbon tubular layers, which effectively prevent their decomposition (even when the samples are put into water or exposed to atmosphere for several months). We have systematically analyzed for the first time the Mg3N2 nanomaterial by means of transmission electron microscopy (TEM), high-resolution TEM, and electron diffraction. Successful fabrication of carbon sheath protected Mg3N2 nanowires may promote further experimental studies on their crystal structures and properties. [ABSTRACT FROM AUTHOR]

One-dimensional ZnO nanostructures with different morphologies have been successfully synthesized through a simple round-to-round metal vapor deposition route at 550 °C with a zinc powder covered indium film as the source material. The structures and morphologies of the products were characterized in detail by using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Studies found that the morphology of the products can be easily tuned from one experimental round to another. Possible growth mechanisms for the formation of one-dimensional ZnO nanostructures with different morphologies are discussed. Photoluminescence studies show that there are sharp UV emission and broad defect-related green emissions for the products obtained in all experimental rounds. Relative intensity of the UV emission to defect-related emissions gradually increased from one experimental round to another. [ABSTRACT FROM AUTHOR]

Graphene as a coating material that shows high impermeability as an excellent barrier in oxidation and corrosion protection has been reported to be less stable at elevated temperature. Sometimes the formed galvanic cell between the graphene and protective surface will even increase the corrosion speed. In comparison, boron nitride (BN), which shows the same impermeability with graphene, is believed to be a better coating material with its superior thermal and chemical inertness. In this study, an in situ synthesis of BN coatings, grown by boron ink, on both carbon and Cu for anti-oxidation and anti-corrosion purposes has been demonstrated. Thermogravimetric analysis and electrochemical analysis reveal that the BN coatings can effectively prevent the carbon from being oxidized at high temperature in air and adequately slow down the corrosion rate of Cu in sodium chloride solution, respectively. These results indicate that boron ink assisted in situ BN coating has high potential in the applications of oxidation and corrosion protection. [ABSTRACT FROM AUTHOR]

Polymer composites with enhanced mechanical, thermal or optical performance usually suffer from poor ductility induced by confined mobility of polymer chains. Herein, highly ductile UV-shielding polymer composites are successfully fabricated. Boron nitride (BN) materials, with a wide band gap of around ∼6.0 eV, are used as fillers to achieve the remarkably improved UV-shielding performance of a polymer matrix. In addition, it is found that spherical morphology BN as a filler can keep the excellent ductility of the composites. For a comparison, it is demonstrated that traditional fillers, including conventional BN powders can achieve the similar UV-shielding performance but dramatically decrease the composite ductility. The mechanism behind this phenomenon is believed to be lubricant effects of BN nanospheres for sliding of polymer chains, which is in consistent with the thermal analyses. This study provides a new design to fabricate UV-shielding composite films with well-preserved ductility. [ABSTRACT FROM AUTHOR]

Thermally conductive and electrically insulating polymer/boron nitride (BN) nanocomposites are highly attractive for various applications in many thermal management fields. However, so far most of the preparation methods for polymer/BN nanocomposites have usually caused difficulties in the material post processing. Here, an in situ grafting approach is designed to fabricate thermally conductive, electrically insulating and post-melt processable polystyrene (PS)/BN nanosphere (BNNS) nanocomposites by initiating styrene (St) on the surface functionalized BNNSs via reversible addition fragmentation chain transfer polymerization. The nanocomposites exhibit significantly enhanced thermal conductivity. For example, at a St/BN feeding ratio of 5:1, an enhancement ratio of 1375% is achieved in comparison with pure PS. Moreover, the dielectric properties of the nanocomposites show a desirable weak dependence on frequency, and the dielectric loss tangent of the nanocomposites remains at a very low level. More importantly, the nanocomposites can be subjected to multiple melt processing to form different shapes. Our method can become a universal approach to prepare thermally conductive, electrically insulating and melt-processable polymer nanocomposites with diverse monomers and nanofillers. [ABSTRACT FROM AUTHOR]

As a structural analogue of the carbon nanotube (CNT), the boron nitride nanotube (BNNT) has become one of the most intriguing non-carbon nanostructures. However, up to now the pre-existing restrictions/limitations of BNNT syntheses have made the progress in their research rather modest. This work presents a new route toward the synthesis of highly pure ultrafine BNNTs based on a modified boron oxide (BO) CVD method. A new effective precursor--a mixture of Li2O and B--has been proposed for the growth of thin, few-layer BNNTs in bulk amounts. The Li2O utilized as the precursor plays the crucial role for the present nanotube growth. The prepared BNNTs have average external diameters of sub-10 nm and lengths of up to tens of um. Electron energy loss spectrometry and Raman spectroscopy demonstrate the ultimate phase purity of the ultrafine BNNTs. Property studies indicate that the ultrafine nanotubes are perfect electrical insulators exhibiting superb resistance to oxidation and strong UV emission. Moreover, their reduced diameters lead to a dramatically decreased population of defects within the tube walls and result in the observation of near-band-edge (NBE) emission at room temperature. [ABSTRACT FROM AUTHOR]

Boron nitride (BN) microtubes were synthesized in a vertical induction furnace using Li2CO3 and B reactants. Their structures and morphologies were investigated using x-ray diffraction, scanning and transmission electron microscopy, and energy-dispersive x-ray spectroscopy. The microtubes have diameters of 1-3 um, lengths of up to hundreds of micrometers, and well-structured ultrathin walls only [?]50 nm thick. A mechanism combining the vapor-liquid-solid (VLS) and template self-sacrificing processes is proposed to explain the formation of these novel one-dimensional microstructures, in which the Li2O-B2O3 eutectic reaction plays an important role. Cathodoluminescence studies show that even at room temperature the thin-walled BN microtubes can possess an intense band-edge emission at [?]216.5 nm, which is distinct compared with other BN nanostructures. The study suggests that the thin-walled BN microtubes should be promising for constructing compact deep UV devices and find potential applications in microreactors and microfluidic and drug delivery systems. [ABSTRACT FROM AUTHOR]