Planar Boron Nitride Research Articles

Interactions of the Aβ(1-42) Peptide with Boron Nitride Nanoparticles of Varying Curvature in an Aqueous Medium: Different Pathways to Inhibit β-Sheet Formation.

The aggregation of amyloid β (Aβ) peptide triggered by its conformational changes leads to the commonly known neurodegenerative disease of Alzheimer's. It is believed that the formation of β sheets of the peptide plays a key role in its aggregation and subsequent fibrillization. In the current study, we have investigated the interactions of the Aβ(1-42) peptide with boron nitride nanoparticles and the effects of the latter on conformational transitions of the peptide through a series of molecular dynamics simulations. In particular, the effects of curvature of the nanoparticle surface are studied by considering boron nitride nanotubes (BNNTs) of varying diameter and also a planar boron nitride nanosheet (BNNS). Altogether, the current study involves the generation and analysis of 9.5 μs of dynamical trajectories of peptide-BNNT/BNNS pairs in an aqueous medium. It is found that BN nanoparticles of different curvatures that are studied in the present work inhibit the conformational transition of the peptide to its β-sheet form. However, such an inhibition effect follows different pathways for BN nanoparticles of different curvatures. For the BNNT with the highest surface curvature, i.e., (3,3) BNNT, the nanoparticle is found to inhibit β-sheet formation by stabilizing the helical structure of the peptide, whereas for planar BNNS, the β-sheet formation is prevented by making more favorable pathways available for transitions of the peptide to conformations of random coils and turns. The BNNTs with intermediate curvatures are found to exhibit diverse pathways of their interactions with the peptide, but in all cases, essentially no formation of the β sheet is found whereas substantial β-sheet formation is observed for Aβ(1-42) in water in the absence of any nanoparticle. The current study shows that BN nanoparticles have the potential to act as effective tools to prevent amyloid formation from Aβ peptides.

A Concurrent Enhancement of Both In‐Plane and Through‐Plane Thermal Conductivity of Injection Molded Polycarbonate/Boron Nitride/Alumina Composites by Constructing a Dense Filler Packing Structure

AbstractIn this work, a facile strategy is proposed to concurrently enhance both in‐plane and through‐plane thermal conductivity of injection molded polycarbonate (PC)‐based composites by constructing a dense filler packing structure with planar boron nitride (BN) and spherical alumina (Al2O3) particles. The state of orientation of BN platelets is altered with the presence of Al2O3, which is favorable for improving both in‐plane and through‐plane thermal conductivity of subsequent moldings. Rheological analysis showed that the formation of intact thermal conductive pathways is crucial to the overall enhancement of thermal conductivity. Both in‐plane and through‐plane thermal conductivity of PC/BN(20 wt%)/Al2O3(40 wt%) composites reached as high as 1.52 and 1.09 W mK−1, which are 485% and 474% higher than that of pure PC counterparts, respectively. Furthermore, the prepared samples demonstrated excellent electrical insulation and dielectric properties which show potential application in electronic and automotive industries.

Plasmon-Acoustic Transducers Based on Graphene–2D Boron Nitride Structures for the Terahertz-Frequency Range

Graphene and 2D hexagonal boron nitride isomorphic to it are promising materials for application in nanoacoustics. Therefore, more detailed study on the possibilities of the development of plasmon-acoustic transducers for nanoacoustics with corresponding numerical estimations of their technical characteristics seems urgent. In this work, the possibility in principle of forming plasmon-acoustic transducers for nanoacoustic devices operating in the terahertz-frequency range is substantiated theoretically and via numerical calculations. A plasmon-acoustic transducer consisting of two subsystems, notably, piezoelectric and plasmon-polariton subsystems, is investigated as the analyzed model. The piezoelectric subsystem is made in the form of a hexagonal boron-nitride nanoribbon—an acoustic duct, the end part of which serves as a piezoelectric transducer exciting elastic waves of the terahertz range. The acoustic duct is overlapped with the plasmon-polariton subsystem in the form of a graphene nanoribbon, in which TM-polarized surface plasmon-polaritons propagate. The introduced electrical impedance of the piezoelectric subsystem and characteristic impedance of the plasmon-polariton subsystem are calculated. It is shown that their values can provide the optimal coordination of a load (the acoustic duct) with the plasmon-polariton waveguide. It is found that graphene nanoplasmonics and nanoacoustics based on piezoelectric planar boron nitride combine well with each other. This opens up broad opportunities for the development of a new class of nanoelectronic devices.

Reply to “Comment on ‘Piezoelectricity in planar boron nitride via a geometric phase' ”

In relation to our original paper [M. Droth et al., Phys. Rev. B 94, 075404 (2016)], the Comment by Li et al. [Phys. Rev. B 98, 167403 (2018)] claims to have identified a "mistake in constructing the adiabatic process of the piezoelectricity". More specifically, they write that in our original work "the erroneous usage of the polarization difference formula in Eq. (4) leads to an invalid analytical expression of piezoelectric constant in Eq. (12) of Reference 1". We explain below why these and other minor claims in the Comment are unwarranted, and why we maintain that our result is correct and physically sound.

Model spin-orbit coupling Hamiltonians for graphene systems

We present a detailed theoretical study of effective spin-orbit coupling (SOC) Hamiltonians for graphene based systems, covering global effects such as proximity to substrates and local SOC effects resulting, for example, from dilute adsorbate functionalization. Our approach combines group theory and tight-binding descriptions. We consider structures with global point group symmetries $D_{6h}$, $D_{3d}$, $D_{3h}$, $C_{6v}$, and $C_{3v}$ that represent, for example, pristine graphene, graphene mini-ripple, planar boron-nitride, graphene on a substrate and free standing graphone, respectively. The presence of certain spin-orbit coupling parameters is correlated with the absence of the specific point group symmetries. Especially in the case of $C_{6v}$---graphene on a substrate, or transverse electric field---we point out the presence of a third SOC parameter, besides the conventional intrinsic and Rashba contributions, thus far neglected in literature. For all global structures we provide effective SOC Hamiltonians both in the local atomic and Bloch forms. Dilute adsorbate coverage results in the local point group symmetries $C_{6v}$, $C_{3v}$, and $C_{2v}$ which represent the stable adsorption at hollow, top and bridge positions, respectively. For each configuration we provide effective SOC Hamiltonians in the atomic orbital basis that respect local symmetries. In addition to giving specific analytic expressions for model SOC Hamiltonians, we also present general (no-go) arguments about the absence of certain SOC terms.

Predicting elastic properties of single-walled boron nitride nanotubes and nanocones using an atomistic-continuum approach

An atomistic-continuum approach is used to investigate structural parameters and elastic properties of boron nitride nanotubes and nanocones. A representative cell that each atom is connected to three neighboring atoms by B–N covalent bonds is selected and a higher-order gradient theory is adopted to derive the constitutive relationship. It is found that the chirality has an effect on structural parameters and elastic properties of tubes and cones but the effect decreases as the radius increases. The apex angle has an apparently decreasing effect on side edge’s Young’s moduli of cones but an increasing effect on circumferential Young’s moduli, and the effect becomes smaller and smaller as the chiral angle increases. As the radius increases, the effect of both chirality and apex angle decreases, and elastic properties and structural parameters of tubes and cones tend toward those of planar boron nitride sheet.

High thermal conductivity epoxy composites with bimodal distribution of aluminum nitride and boron nitride fillers

High thermal-conductivity fillers of aluminum nitride (AlN) and boron nitride (BN) were incorporated in the epoxy matrix in order to identify the effects of the particle size and the relative composition on the thermal conductivity of composites. In the bimodal distribution of polygonal AlN and planar BN particles, the optimal thermal conductive path was strongly affected by the packing efficiency and interfacial resistance of the particles in a sensitive way and, consequently, the maximum thermal conductivity was achieved up to 8.0W/mK in the 1:1 volume ratio of AlN:BN particles. In the optimal volume ratio of the two fillers at 1:1, the relative filler size, which was represented by the shape factor (or the diameter ratio of the two filler particles, RD), also influenced the thermal conductivity giving the maximum conductivity at the shape factor RD≈1. The optimal morphology and composition of the AlN/BN composite systems were clearly visualized and thoroughly discussed in the filler distribution curves plotting the filler-appearance frequency as a function of particle size. The developed methodology validated that two different particles should be packed well to fill up the interstitial space and, simultaneously, the contact resistance and the contact area of the fillers should be optimized to maximize the thermal conductivity.

Pyrolytic carbon layers—an electron spin resonance analysis

Chemical vapour infiltration is simulated by deposition of pyrolytic carbon on planar boron nitride substrates and carbon fibers in a hot-wall tubular reactor at about 1100 °C for varied pressure and flow-velocity of methane. The degree of orientation of the deposited graphite-like domains can be monitored via orientation and temperature dependence of the electron spin resonance parameters (g-tensor, linewidth). The electronic structure of the localized defects and conduction electrons is accessible by a quantitative modelling of these parameters. The interaction of the built-in hydrogen atoms with the unpaired electron spins is analysed by electron–proton spin double resonance technique (Overhauser shift)

Electric polarization of heteropolar nanotubes as a geometric phase.

The threefold symmetry of planar boron nitride (BN), the III-V analog to graphene, prohibits an electric polarization in its ground state, but this symmetry is broken when the sheet is wrapped to form a BN nanotube. We show that this leads to an electric polarization along the nanotube axis which is controlled by the quantum mechanical boundary conditions on its electronic states around the tube circumference. Thus the macroscopic dipole moment has an intrinsically nonlocal quantum mechanical origin from the wrapped dimension. We formulate this novel phenomenon using the Berry's phase approach and discuss its experimental consequences.

Discussion of “Anomalous Boron Diffusion in Silicon from Planar Boron Nitride Sources” [J. Stach and A. Turley (pp. 722–724, Vol. 121, No. 5)

not Available.

Overlap functions in planar crystals

The overlap function F2 = ¦∫ u∗k(r)uk'(r)dr¦2 is evaluated for several values of k and a wide mesh of points k', where uk is the modulating part of the Bloch wave function for a π-electron in the valence or conduction band, in planar boron nitride and graphite. It is found that for boron nitride, if uk and uk, are in the same band and ¦k — k'¦ is less than a quarter of the radius of the Brillouin zone, then F2 usually lies between 0.9 and 1. In graphite, however, F2 behaves more erratically because the top of the valence band is degenerate with the bottom of the conduction band; a theoretical analysis of this behaviour is also presented.