The nature of a selective peak in the BK-absorption edge spectrum and the electronic energy band structure of the crystal 3C BN0.99

A new interpretation of the nature of the resonance in the quantum-yield K spectra of boron in the crystal 3C BN is proposed. This interpretation is based on calculation of the electronic energy band structure of the nonstoichiometric boron nitride 3C BN_0.99, which is carried out by the local coherent potential method in the multiple-scattering approximation. The tops of the valence band and of the XANES range of nonstoichiometric and perfect crystals of boron nitride are compared with the x-ray photoelectron spectrum of 3C BN and the BK-absorption edge spectrum. The electronic states near the BK-absorption edge are modeled and discussed for the relaxed and metastable states caused by the formation of vacancies in the nitrogen sublattice.     

Electronic band structure and x-ray spectra of boron nitride polytypes

The electronic band structures of boron nitride crystal modifications of the graphite (h-BN), wurtzite (w-BN), and sphalerite (c-BN) types are calculated using the local coherent potential method in the cluster muffin-tin approximation within the framework of the multiple scattering theory. The specific features of the electronic band structure of 2H, 4H, and 3C boron nitride polytypes are compared with those of experimental x-ray photoelectron, x-ray emission, and K x-ray absorption spectra of boron and nitrogen. The features of the experimental x-ray spectra of boron nitride in different crystal modifications are interpreted. It is demonstrated that the short-wavelength peak revealed in the total densities of states (TDOS) in the boron nitride polytypes under consideration can be assigned to the so-called outer collective band formed by 2p electrons of boron and nitrogen atoms. The inference is made that the decrease observed in the band gap when changing over from wurtzite and sphalerite to hexagonal boron nitride is associated with the change in the coordination number of the components, which, in turn, leads to a change in the energy location of the conduction band bottom in the crystal.     

Specific features of the electronic band structure and x-ray spectra of boron nitride in sphalerite and wurtzite modifications

The electronic band structure of boron nitride compounds with crystal lattices of the sphalerite (c-BN) and wurtzite (w-BN) types is calculated by the local coherent potential method in the cluster muffin-tin approximation within the framework of the multiple scattering theory. The local partial densities of 2p states for boron and nitrogen in c-BN and w-BN modifications are compared with the experimental boron and nitrogen K x-ray emission spectra and band-structure calculations. A comparison of the total densities of states in c-BN and w-BN with the x-ray photoelectron spectra and the band calculations has revealed both similarities and differences in the electronic structures of these modifications. The fine structure in the vicinity of the valence band top of boron nitride in different crystal modifications is theoretically calculated for the first time. The specific features of the electronic structure and the x-ray spectra of boron nitride in different modifications are discussed.     

Fluid synthesis and structure of a new polymorphic modification of boron nitride

A new previously unknown phase of boron nitride with a hardness of 0.41–0.63 GPa has been pre-pared by the supercritical fluid synthesis. The presence of a new phase is confirmed by the X-ray spectra and IR absorption spectra, where new reflections and bands are distinguished. The fundamental reflection of the X-ray diffraction pattern is d = 0.286–0.291 nm, and the characteristic band in the infrared absorption spectrum is observed at 704 cm^?1. The X-ray diffraction pattern and the experimental and theoretical infrared absorption spectra show that a new synthesized boron nitride phase can be a cluster crystal (space group 211) with a simple cubic lattice. Cage clusters of a fullerene-like morphology B₂₄N₂₄ with point symmetry O are arranged in lattice sites.     

Effects of endohedral element in B24N24 clusters on hydrogenation studied by molecular orbital calculations

Possibility of hydrogen gas storage in boron nitride (BN) clusters was investigated by molecular orbital calculations. Chemisorption calculation was carried out for B₂₄N₂₄ with changing endohedral elements in BN cluster to compare the bonding energy at nitrogen and boron, which showed that Li is a suitable element for hydrogenation to B₂₄N₂₄.     

Electronic,structural, and thermal properties of a nanocable consisting of carbon and BN nanotubes

The band structure and thermal behavior of a coaxial C/BN nanocable (5,5)C@(17,0)BN consisting of a carbon nanotube and a boron nitride nanotube have been studied using a tight-binding approximation based on density functional theory. The system is stable up to T～3500–3700 K. As the temperature increases, deformations of the BN tube begin earlier than those of the carbon tube. The near-Fermi states of the nanocable are formed by the overlapping π-π* bands of the carbon tube, and the outer BN nanotube (the nanocable sheath) is an insulator with a bandgap of ～4 eV. The electronic properties of the nanocable (the metallic-type conductivity of the C tube and the insulating character of the BN tube) are retained over the entire temperature interval.     

Fluid synthesis and structure of a new boron nitride polymorph—hyperdiamond fulborenite B<Subscript>12</Subscript>N<Subscript>12</Subscript> (<Emphasis Type="Italic">E</Emphasis> phase)

A new boron nitride polymorph is prepared for the first time by supercritical fluid synthesis in a high-pressure gazostat at a pressure P < 200 MPa and a temperature T < 1000°C in various atmospheres. The formation of the new phase is confirmed by x-ray diffraction and infrared absorption spectroscopy. A number of lines in the x-ray diffraction patterns and infrared absorption spectra of the new phase coincide with those described in the literature for the so-called E phase. On this basis, the conclusion is drawn that the E phase of boron nitride is most likely formed during supercritical fluid synthesis. Since the structure of the E phase is as yet unknown, a model structure of the new phase is proposed in the form of a diamond-like lattice with the sites occupied by molecules of the fulborene B₁₂N₁₂. The proposed structure is confirmed by the good agreement between the calculated and experimental values of the lattice parameters (A = 1.152 and 1.114 nm, respectively), densities (ρ = 2.59 and 2.50–2.60 g/cm³, respectively), and x-ray diffraction patterns. This new boron nitride zeolite with a faujasite lattice is given the name hyperdiamond fulborenite B₁₂N₁₂. The calculated bulk modulus of the hyperdiamond fulborenite B = 658 GPa is higher than that of diamond.     

Theoretical study on structure of boron nitride fullerenes

We propose the parameters of the Stillinger-Weber potential for hexagonal boron nitride (BN) structures. For the reliability of these parameters, the structural property of BN fullerenes is investigated. The stability of BN fullerenes increases with increasing the number of atoms, due to the reduction of the curvature effect of BN fullerenes. The structures of the relative stable fullerenes are B₁₆N₁₆, B₁₈N₁₈, B₂₂N₂₂, B₂₅N₂₅, and B₂₈N₂₈.     

Electronic structure of BN nanotubes with intrinsic defects NB and BN and isoelectronic substitutional impurities PN, AsN, SbN, InB, GaB, and AlB

The effect of intrinsic defects and isoelectronic substitutional impurities on the electronic structure of boron-nitride (BN) nanotubes is investigated using a linearized augmented cylindrical wave method and the local density functional and muffin-tin approximations for the electron potential. In this method, the electronic spectrum of a system is governed by a free movement of electrons in the interatomic space between cylindrical barriers and by a scattering of electrons from the atomic centers. Nanotubes with extended defects of substitution N_B of a boron atom by a nitrogen atom and, vice versa, nitrogen by boron B_N with one defect per one, two, and three unit cells are considered. It is shown that the presence of such defects significantly affects the band structure of the BN nanotubes. A defect band π(B, N) is formed in the optical gap, which reduces the width of the gap. The presence of impurities also affects the valence band: the widths of s, sp, and p_π bands change and the gap between s and sp bands is partially filled. A partial substitution of the N by P atoms leads to a decrease in the energy gap, to a separation of the Ds(P) band from the high-energy region of the s(B, N) band, as well as to the formation of the impurity Dπ(P) and Dπ*(P) bands, which form the valence-band top and conduction-band bottom in the doped system. The influence of partial substitution of N atoms by the As atom on the electronic structure of BN nanotubes is qualitatively similar to the case of phosphorus, but the optical gap becomes smaller. The optical gap of the BN tubule is virtually closed due to the effect of one Sb atom impurity per translational unit cell, in contrast to the weak indium-induced perturbation of the band structure of the BN nanotube. Introduction of the one In, Ga or Al atom per three unit cells of the (5, 5) BN nanotube results in 0.6 eV increase of the optical gap. The above effects can be detected by optical and photoelectron spectroscopy methods, as well as by measuring electrical properties of the pure and doped BN nanotubes. They can be used to design electronic devices based on BN nanotubes.     

Radiation resistance of boron nitride and related ceramics to low-energy electron irradiation

The radiation resistance of heat-proof ceramics based on boron nitride (BN + Si₃N₄ and BN + SiO₂), which are proposed to be used as structural materials in space ion engines, to low-energy electron irradiation has been investigated.     

Effect of doping on electronic properties of double-walled carbon and boron nitride hetero-nanotubes

The effect of boron nitride (BN) doping on electronic properties of armchair double-walled carbon and hetero-nanotubes is studied using ab initio molecular dynamics method. The armchair double-walled hetero-nanotubes are predicted to be semiconductor and their electronic structures depend strongly on the electronic properties of the single-walled carbon nanotube. It is found that electronic structures of BN-doped double-walled hetero-nanotubes are intermediate between those of double-walled boron nitride nanotubes and double-walled carbon and boron nitride hetero-nanotubes. Increasing the amount of doping leads to a stronger intertube interaction and also increases the energy gap.     

Hydrogen storage in boron nitride and carbon clusters studied by molecular orbital calculations

Possibility of hydrogen gas storage in carbon (C) and boron nitride (BN) clusters was investigated by molecular orbital calculations. Chemisorption calculation was carried out for C₆₀, B₂₄N₂₄ and B₃₆N₃₆ with changing position of hydrogen atom to compare the bonding energy at carbon, nitrogen and boron, tetragonal and hexagonal rings. Chemisorption calculation of hydrogen for BN clusters showed that hydrogen bondings with nitrogen atoms and tetragonal rings were the most stable. Stability of H₂ molecules inside BN and C clusters was also investigated by molecular orbital calculations. C and BN clusters showed possibility of hydrogen storage of 6.5 and 4.9 wt%, respectively.     

The effect of concentration of <Emphasis Type="Bold">H</Emphasis> <Subscript> <Emphasis Type="Bold">2</Emphasis> </Subscript> physisorption on the current–voltage characteristic of armchair BN nanotubes in CNT–BNNT–CNT set

In this research, we have studied physisorption of hydrogen molecules on armchair boron nitride (BN) nanotube (3,3) using density functional methods and its effect on the current–voltage (I–V) characteristic of the nanotube as a function of concentration using Green’s function techniques. The adsorption geometries and energies, charge transfer and electron transport are calculated. It is found that H₂ physisorption can suppress the I–V characteristic of the BN nanotube, but it has no effect on the band gap of the nanotube. As the H₂ concentration increases, under the same applied bias voltage, the current through the BN nanotube first increases and then begins to decline. The current–voltage characteristic indicates that H₂ molecules can be detected by a BN-based sensor.     

Analytical optimization of the lattice parameter using the binding energy calculated in the quasi-classical approximation

The dependence of the static binding energy of a crystal on the crystal structure as calculated in the initial quasi-classical approximation is shown to allow the equilibrium lattice parameter to be found analytically. The application of this method to boron nitride modifications leads to lattice parameters that coincide with experimental values to within several percent. This method gives lattice parameters of 2.66, 3.49, and 2.44 Å for the BN hexagonal layer and the cubic c-BN and “ideal” wurtzite-like w-BN crystals, respectively. The corresponding binding energies are estimated to be 23.2, 14.1, and 13.6 eV/mol, respectively.     

Photoluminescence of hexagonal boron nitride: Effect of surface oxidation under UV-laser irradiation

We report on the UV laser-induced fluorescence of hexagonal boron nitride (h-BN) following nanosecond laser irradiation under vacuum and in different environments of nitrogen gas and ambient air. The observed fluorescence bands are tentatively ascribed to impurity and mono (V_N) or multiple (m-V_N with m=2 or 3) nitrogen vacancies. A structured fluorescence band between 300 and 350 nm is assigned to impurity-band transition and its complex lineshape is attributed to phonon replicas. An additional band at 340 nm, assigned to V_N vacancies on surface, is observed under vacuum and quenched by adsorbed molecular oxygen. UV-irradiation of h-BN under vacuum results in a broad asymmetric fluorescence at ∼400 nm assigned to m-V_N vacancies; further irradiation breaks more B-N bonds enriching the surface with elemental boron. However, no boron deposit appears under irradiation of samples in ambient atmosphere. This effect is explained by oxygen healing of radiation-induced surface defects. Formation of the oxide layer prevents B-N dissociation and preserves the bulk sample stoichiometry.     

Physical properties of Ima2-BN under pressure: First principles calculations

A fully orthorhombic boron nitride (BN) polymorph with an orthorhombic symmetry (Ima2-BN, space group: Ima2) was investigated by first-principles calculations. The Ima2-BN under 30 GPa is both mechanically and dynamically stable via elastic constants and phonon spectra. The anisotropic and electronic properties of Ima2-BN under different pressure are investigated in this work. The anisotropic properties calculations show that the Young's modulus of Ima2-BN in (001) plane exhibits the greatest anisotropy under ambient pressure, while in (111) plane it is the greatest when P > 20 GPa, while the (010) plane has always exhibited the minimal anisotropy whether under ambient pressure or high pressure. Ima2-BN is an indirect wider band gap semiconductor material under ambient pressure, and the band gap of Ima2-BN decreases with the increasing pressure. The minimum thermal conductivities κ_min of Ima2-BN is 1.85 W/(cmK), it is slightly higher than of B₄N₄-I and c-BN.     

Electronic properties of silicene in BN/silicene van der Waals heterostructures

Silicene is a promising 2D Dirac material as a building block for van der Waals heterostructures(vd WHs). Here we investigate the electronic properties of hexagonal boron nitride/silicene(BN/Si) vd WHs using first-principles calculations.We calculate the energy band structures of BN/Si/BN heterostructures with different rotation angles and find that the electronic properties of silicene are retained and protected robustly by the BN layers. In BN/Si/BN/Si/BN heterostructure, we find that the band structure near the Fermi energy is sensitive to the stacking configurations of the silicene layers due to interlayer coupling. The coupling is reduced by increasing the number of BN layers between the silicene layers and becomes negligible in BN/Si/(BN)_3/Si/BN. In(BN)_n/Si superlattices, the band structure undergoes a conversion from Dirac lines to Dirac points by increasing the number of BN layers between the silicene layers. Calculations of silicene sandwiched by other 2D materials reveal that silicene sandwiched by low-carbon-doped boron nitride or HfO_2 is semiconducting.     

Domain growth and aging scaling in coarsening disordered systems

We explore the electronic and transport properties out of a biased multilayer hexagonal boron nitride (h-BN) by first-principles calculations. The band gaps of multilayer h-BN decrease almost linearly with increasing perpendicular electric field, irrespective of the layer number N and stacking manner. The critical electric filed (E ₀) required to close the band gap decreases with the increasing N and can be approximated by E ₀ = 3.2 / (N ? 1) (eV). We provide a quantum transport simulation of a dual-gated 4-layer h-BN with graphene electrodes. The transmission gap in this device can be effectively reduced by double gates, and a high on-off ratio of 3000 is obtained with relatively low voltage. This renders biased MLh-BN a promising channel in field effect transistor fabrication.     

Analysis of the polarization dependence of the N K edge X-ray absorption fine structure in InN

The polarization dependence of the x-ray absorption near-edge structure (XANES) of InN beyond the N K edge is calculated. The XANES calculations are performed for different values of the angle θ between the XY plane of crystalline indium nitride and the incident x-radiation (θ = 15°, 30°, 45°, 60°, 75°, and 90°). It is shown that, in the case of N K XANES for InN, a strong polarization dependence of the specific features of the spectrum is observed. The calculated spectra are compared with previously measured experimental spectra. The partial densities of the electronic states of InN are calculated near the top of the valence band and near the bottom of the conduction band.     

First-principles study of nanotubes within the tetragonal,hexagonal and dodecagonal cycle structures

A systematic study has been done on the structural and electronic properties of carbon, boron nitride and aluminum nitride nanotubes with structure consisting of periodically distributed tetragonal (T ≡A₂X₂), hexagonal (H ≡A₃X₃) and dodecagonal (D ≡A₆X₆) (AX=C₂, BN, AlN) cycles. The method has been performed using first-principles calculations based on density functional theory (DFT). The optimized lattice parameters, density of state (DOS) curves and band structure of THD-NTs are obtained for (3, 0) and (0, 2) types. Our calculation results indicate that carbon nanotubes of these types (THD-CNTs) behave as a metallic, but the boron nitride nanotubes (THD-BNNTs) (with a band gap of around 4 eV) as well as aluminum nitride nanotubes (THD-AlNNTs) (with a band gap of around 2.6 eV) behave as an semiconductor. The inequality in number of atoms in different directions is affected on structures and diameters of nanotubes and their walls curvature.