Boron Nitride Sheets Research Articles

Energy Gaps in BN/GNRs Planar Heterostructure.

Using the tight-binding approach, we study the band gaps of boron nitride (BN)/ graphene nanoribbon (GNR) planar heterostructures, with GNRs embedded in a BN sheet. The width of BN has little effect on the band gap of a heterostructure. The band gap oscillates and decreases from 2.44 eV to 0.26 eV, as the width of armchair GNRs, , increases from 1 to 20, while the band gap gradually decreases from 3.13 eV to 0.09 eV, as the width of zigzag GNRs, , increases from 1 to 80. For the planar heterojunctions with either armchair-shaped or zigzag-shaped edges, the band gaps can be manipulated by local potentials, leading to a phase transition from semiconductor to metal. In addition, the influence of lattice mismatch on the band gap is also investigated.

Structural stability and electronic characteristics of cellulose nanowires on graphene-like systems

The adsorption of two kinds of cellulose chains on graphene and boron-nitride (insulating and semi-conducting) sheets were studied using first principles density-functional theory calculations. The effect of adsorption was analyzed in terms of the binding energy, band-structure, density of states, charge density differences and current behavior. The stable conformations demonstrate the possibilities of creating bio-conducting materials important for various applications utilizing cellulose, one of the most abundant biopolymers in nature. The charge-density differences reveal the charge accumulation on the atoms of the substrates/cellulose depending on the type of atom. Moreover, the increase in conductivity of the combined systems compared to the biopolymer as is evident from the current vs bias voltage study indicates the conducting nature of the systems.

Mechanical properties of nanocracks in hybrid graphene/hexagonal boron nitride sheets

Mechanical properties of nanocracks in hybrid graphene/hexagonal boron nitride sheets

Valley polarized conductance quantization in bilayer graphene narrow quantum point contact

In this study, we fabricated quantum point contacts narrower than 100 nm by using an electrostatic potential to open the finite bandgap by applying a perpendicular electric field to bilayer graphene encapsulated between hexagonal boron nitride sheets. The conductance across the quantum point contact was quantized at a high perpendicular-displacement field as high as 1 V/nm at low temperature, and the quantization unit was 2e2/h instead of mixed spin and valley degeneracy of 4e2/h. This lifted degeneracy state in the quantum point contact indicates the presence of valley polarized state coming from potential profile or effective displacement field in one-dimensional channel.

Enhanced thermal management performance of comb-like polymer/boron nitride composite phase change materials for the thermoregulated fabric application

In this paper, a series of composite PCMs based on the comb-like polymer, poly(tetradecyl acrylate) (PTA), is developed via a solution-blending method with boron nitride (BN) as the thermal conductors that vary from 5%, 10%, 15% to 20%. The structure, thermal performance, energy storage and release capability, cycle stability are deeply characterized. The thermal conductivity of PTA/BN composite PCMs increases to 0.62 W/mK at 20% BN, displaying 113.8% higher than that of pure PTA (0.29 W/mK). The PTA/BN composite PCMs present a good energy storage ability, and the maximum temperature difference, -22.3 °C, and 475 s thermal buffering time at 50 °C are achieved for the coated fabric by 0.96 g PTA/BN-20% composites. And, the fabrics coated by PTA/BN-20% demonstrate good structure stability with no thermal energy loss after 5 thermal cycles. In the meantime, a comparable temperature increases to 6.1 °C is displayed for the bottle covered by the PTA/BN PCMs coated fabric, followed by a stable thermal energy storage ability during the 5 min heating process, expressing the good thermal conductor of the BN sheet. This result opens a promising application for the thermoregulated fabric with a controlled thermal conductivity and thermal energy storage ability.

Dipole orientation variation of hydration shell around alkali metal cation on hexagonal boron nitride sheet

Orientation arrangement of hydration shells for hydrated cation plays an important role in solid–liquid interfaces. However, there is still poor understanding about the structure of the hydration shells formed at the solid–liquid interface. In this paper, we study the structures and interaction of typical hydrated alkali metal cation (Li+, Na+ and K+) on the flat polar material surface of the hexagonal boron nitride (h-BN) sheet by increasing the number of water molecules from n = 1 to n = 9 through the artificial bee colony (ABC) algorithm and density functional theory calculations. The hydration shell around alkali metal cation could be divided into two groups, one is Li+-(H2O)n and Na+-(H2O)n and the other is K+-(H2O)n. The orientation of hydration shell for K+-(H2O)n complexes exhibits stronger anisotropy behaviour than both Li+-(H2O)n and Na+-(H2O)n complexes on the h-BN sheet. It is found that the stronger orientation anisotropy of K+-(H2O)n originates from the weak cation-hydration energy and its weak influence upon the π-K+ interaction. Our findings provide valuable insights into the microscopic details of the structures and adsorption of hydrated cation on the h-BN sheet.

The Effect of Magnetic Field on Optical Conductivity of Hexagonal Boron-Nitride Sheet

The main purpose of this work is to investigate the effect of external magnetic field on the optical absorption of single-layer hexagonal boron nitride. The optical absorption of the system can be found by calculating the imaginary part of the dielectric function. The optical absorption is proportional to from the real part of the dynamical electrical conductivity function. Based on linear response theory, dynamical conductivity function can be calculated in terms of the current-current correlation function. In this study, the tight-binding model Hamiltonian has been applied to study the electronic band spectrum of the system. Also, the energy spectrum of electrons is calculated in the presence of a magnetic field along perpendicular to the plane. The Green’s function approach has been explored to obtain current-current correlation function and optical conductivity. The results show applying magnetic field has significant effects on dependence of optical absorption of boron nitride system on photon frequency and temperature.

Oxidative Strong Metal-Support Interactions between Metals and Inert Boron Nitride.

The strong metal-support interaction (SMSI) is one of the most important concepts in heterogeneous catalysis, which has been widely investigated between metals and active oxides triggered by reductive atmospheres. Here, we report the oxidative strong metal-support interaction (O-SMSI) effect between Pt nanoparticles (NPs) and inert hexagonal boron nitride (h-BN) sheets, in which Pt NPs are encapsulated by oxidized boron (BOx) overlayers derived from the h-BN support under oxidative conditions. De-encapsulation of Pt NPs has been achieved by washing in water, and the residual ultrathin BOx overlayers work synergistically with surface Pt sites for enhancing CO oxidation reaction. The O-SMSI effect is also present in other h-BN-supported metal catalysts such as Au, Rh, Ru, and Ir within different oxidative atmospheres including O2 and CO2, which is determined by metal-boron interaction and O affinity of metals.

Surface modified boron nitride towards enhanced thermal and mechanical performance of thermoplastic polyurethane composite

Owing to the unpredictable advancement in electronic devices, the demand for highly thermally conductive and electrically insulating material is increasing day by day. Besides, surface treatment of chemically inert hexagonal boron nitride (h-BN) sheets found challenging and a distressing contention towards its acceptable thermal transportation. Herein, h-BN sheets are functionalized with divergent amines (its three isomers) to obtain their astonishing properties like high disperse ability and development of interfacial conduction in polymer composite. This comparative study elucidates the significance of the covalent interaction of amines (-NH2) with h-BN lattice as well as strong hydrogen bonding with thermoplastic polyurethane (TPU) matrix. It is demonstrated that both ortho-phenylenediamine o-PDA-BN and para-phenylenediamine p-PDA-BN filled TPU composites exhibit higher through-plane thermal conductivity (┴TC) of 2.06 and 1.96 W m−1 K−1 respectively by substantially establishing a higher thermal transportation path at high filler loading of 45 wt %. Whereas, meta-phenylenediamine m-PDA-BN composites reveal somewhat low ┴TC of 1.27 W m−1 K−1 at the same filler loading. Interestingly, all fabricated composites consisting of functionalized BN (f-BN) and TPU show unprecedented thermal and mechanical properties at such a high filler loading which demonstrates their great potential for packaging application in microelectronics.

Boron Nitride-Titania Mesoporous Film Heterostructures.

The fabrication of optically active heterostructures in the shape of mesostructured thin films is a highly challenging task. It requires an integrated process to allow in one-step incorporating the two-dimensional materials within the mesoporous ordered host without disrupting the pore organization. Hexagonal boron nitride (BN) nanosheets have been successfully introduced into titania mesoporous films using a template-assisted sol–gel synthesis and evaporation-induced self-assembly. Two types of BN sheets have been used, with and without defects, to investigate the role of defects in heterostructure properties. It has been found that the defects increase the ultraviolet radiation A (UVA) absorbance and enhance the photocatalytic response of the film. The BN sheets are optically transparent and do not exhibit any photocatalytic property but contribute to anatase crystallization via heterogeneous nucleation.

High‐thermal‐conduction and low‐cost composite originated from the tight packing structure of boron nitride sheets and binary alumina balls

AbstractIn this work, a novel low‐cost and thermal conductive composite consisting of boron nitride (BN)/aluminum oxide (Al2O3) heat transfer network was constructed by the high packing volume fraction of two sizes Al2O3 spheres at the optimal weight ratio. The dense packing of 5 μm Al2O3 and 20 μm Al2O3 supports the BN sheets scattering around Al2O3 to interconnect into main three‐dimensional BN network, and acts as thermal conductive bridges forming secondary BN‐Al2O3 heat transfer networks. The maximum thermal conductivity of the composite reached 3.61 Wm−1 K−1, which was 20.1 times more than that of pure epoxy resin. Moreover, the excellent capacity of heat dissipation and the dielectric properties denoted that the composite can be used commendably in electronic components. This article is expected to provide a novel idea for the preparation of economical and high‐performance thermal conductive composites applied in new generation of microelectronic devices.

Electroless deposition surface engineering of boron nitride sheets for enhanced thermal conductivity and decreased interfacial thermal resistance of epoxy composites

Filler surface engineering has become an effective method to improve the thermal conduction performance of polymeric composites. However, most of the surface engineering deposits low thermal conductivity materials on the surface of fillers. The increased interfacial thermal resistance between the functional filler will deteriorate the heat transfer capability of thermal conduction network. In order to construct an excellent thermal conduction network, the electroless deposition surface engineering was successfully designed to decorate the surface of BN sheet with high thermal conductivity metallic copper nanoparticles. Through the full characterization of the BN@CuNP and its epoxy-based composites, the effects of electroless deposition surface engineering on thermal conduction enhancement were investigated. The copper nanoparticles deposited on the surface of BN sheets will make the BN@CuNP fillers possess high thermal conductivity and effectively bridge the BN sheets, thereby exhibiting a synergistic effect in reducing the interfacial thermal resistance and enhancing the heat transfer capability of the BN@CuNP thermal conduction network. With the increase of filler content, the effects of electroless deposition surface engineering on thermal conduction enhancement are continuously promoted. The electroless deposition surface engineering shows great advantages in high thermal conductive composites design and fabrication.

Strong catalyst support interactions in defect-rich γ-Mo2N nanoparticles loaded 2D-h-BN hybrid for highly selective nitrogen reduction reaction

Electrochemical ammonia synthesis by N2 fixation has proven to be a promising alternative to the energy-consuming, befouling Haber-Bosch process. Considering the low faradaic efficiency and sluggish kinetics of Nitrogen Reduction Reaction (NRR), it is significant to design a robust and selective catalyst. Herein, we demonstrate a single step in-situ nitridation method to grow cubic molybdenum nitride (γ-Mo2N) nanoparticles on a 2D hexagonal boron nitride (h-BN) sheets as a potential, cost-effective electrocatalyst for NRR, in which the selectivity for N2 was regulated by interfacially engineering the Mo2N-BN bridge. The maneuverability of h-BN sheets enabled the provocation of N-vacancies governed by the particle size, where the fine-tuning of their significance emanated the highest faradaic efficiency of 61.5 %. Moreover, such non-noble metal-based hybrids delivered a stable performance for 20 h. Therefore, our approach of designing the electronic structure of a catalyst by controlling the defects could be an effective practice for selective NRR.

Chemical exfoliation synthesis of boron nitride and molybdenum disulfide 2D sheets via modified Hummers’ method

Chemical exfoliation synthesis of boron nitride and molybdenum disulfide 2D sheets via modified Hummers’ method

Thin-walled boron nitride micron square tube decorated by nanosheets: Preparation, characterization and adsorption property

A novel one-dimensional boron nitride (BN) microtube hierarchical structure was prepared by the chemical vapour deposition method. XRD, SEM, FTIR, Raman, TEM and HR-TEM were used to characterise BN. The samples demonstrated an average inner diameter of 0.6 μm and a tube length of 5-60 μm. Its surface was loaded with a large number of BN nanosheets. The specific surface area of the BN hierarchical structure reached 130.8 m2 g−1, and the structure exhibited good adsorption property for congo red (CR), methylene blue (MB), and copper ions (Cu2+) with maximum uptake capacities of 328.95, 272.48 and 171.23 mg g−1, respectively. The adsorption of these adsorbates onto the BN microtube was well-fitted with the Langmuir model. Moreover, the samples could be recycled by burning or heating in air. Comparative experimental results indicated that the growth mechanism of BN microtubes followed the vapour-liquid-solid model, whereas the growth mechanism of the surface-loaded ultra-thin BN sheets followed the vapour-solid model.

Fracture behavior dependent on crack-tip shapes in nanoscale crack-defect monolayer boron nitride sheets

ABSTRACT Nanoscale defects, including cracks, circular holes, and the triangular-shaped defects, often occur in the growth of boron nitride nanosheets (BNNS). In this study, the fracture behavior of chiral BNNS with different crack-tip shapes and the interactions of nanoscale crack-defects are studied using molecular dynamics (MD) simulations and finite element (FE) analysis. Both MD and FE results indicate that the fracture strength of BNNS with two crack tips (t = 2) is significantly higher than that with one crack tip (t = 1), in which the difference in zigzag (ZZ) direction is more obvious than that in armchair (AC) direction, mainly due to the fact that the change of bond angles near the crack tips is more substantial in the ZZ direction than those in the AC direction. Our results show that the fracture strength of BNNS strongly depends on crack-tip shapes, chiral angles, the defect-to-crack tip spacing and deflection angles. Checking against the current MD simulations and FE analysis shows the present results are reasonable. This study should be of great importance for enhancing the fracture performance of BNNS by modulating their crack-tip shapes and the interactions of nanoscale crack-defects.

Enhancement of piezoelectric and flexoelectric response of boron nitride sheet superlattices via interface and defect engineering

In this work, the piezoelectric, flexoelectric and elastic coefficients of boron nitride sheet/s (BNS) with graphene stripes were determined via molecular dynamics simulations (MDS) with a Tersoff potential force field. The external electric-field (E-field) was applied in the two most relevant orientations of BNS: armchair and zigzag. Our results reveal that the coherent interface engineering of zigzag stripe and hexagonal ring of graphene with BNS can be utilized to enhance the total electronic response of resulting hybrid BNS. For instance, the increase in total polarizations when the E-field applied in the armchair and zigzag directions of hybrid BNS are found to be 17% and 21%, respectively, compared to pristine BNS due to the interface engineering of BNS/zigzag graphene stripe. Moreover, we determined the elastic properties of hybrid BNS and found that its Young's and shear moduli enhanced by 17.5% and 12%, respectively. The other cases, interface engineering of BNS/hexagonal ring of graphene and defect engineering of Stone-Wales (SW) defected BNS also improved the total polarization of BNS compared to the pristine BNS but lower than the first case. Comparisons of the (i) axial piezoelectric and flexoelectric coefficients of pristine BNS, and (ii) elastic coefficients of pristine and hybrid BNS with the existing results are found to be in good agreement. This study opens up an avenue for enhancing the net polarization as well as the elastic properties of existing BN sheets via integration of graphene stripes in them and defect engineering in general.

High-k Boron Nitride Sheets/Polyimide Hybrid Dielectric Layers for the Fabrication of Flexible Organic Transistors on Commercial Graphite Paper

Organic transistors are crucial components in future flexible electronics due to their excellent properties and ease of circuit integration. Previously, we demonstrated that flexible organic (polyimide) thermal transistors could be prepared using commercial graphite paper as the substrate. These materials exhibited excellent temperature sensitivity, linearity and recoverability due to the intrinsically high thermal conductivity of graphite. In this study, boron nitride (BN) sheets/polyimide hybrid dielectric layers were synthesized for the fabrication of flexible organic transistors using a commercial graphite paper. Under test, the results showed that the introduction of BN sheets was beneficial in improving the mobility and transistor characteristics of the device, as well as enhancing the overall stability. The as-fabricated transistors virtually exhibited no hysteresis at all BN contents.

Realizing a Not-Strong-Not-Weak Polarization Electric Field in Single-Atom Catalysts Sandwiched by Boron Nitride and Graphene Sheets for Efficient Nitrogen Fixation.

Developing efficient single-atom catalysts (SACs) for nitrogen fixation is of great importance while remaining a great challenge. The lack of an effective strategy to control the polarization electric field of SACs limits their activity and selectivity. Here, using first-principles calculations, we report that a single transition metal (TM) atom sandwiched between hexagonal boron nitride (h-BN) and graphene sheets (namely, BN/TM/G) acts as an efficient SAC for the electrochemical nitrogen reduction reaction (NRR). These sandwich structures realize stable and tunable interfacial polarization fields that enable the TM atom to donate electrons to a neighboring B atom as the active site. As a result, the partially occupied pz orbital of a B atom can form B-to-N π-back bonding with the antibonding state of N2, thus weakening the N≡N bond. The not-strong-not-weak electric field on the h-BN surface further promotes N2 adsorption and activation. The NRR catalytic activity of the BN/TM/G system is highly correlated with the degree of positively polarized charges on the TM atom. In particular, BN/Ti/G and BN/V/G are identified as promising NRR catalysts with high stability, offering excellent energy efficiency and suppression of the competing hydrogen evolution reaction.

Exact solutions of bending deflection for single-walled BNNTs based on the classical Euler–Bernoulli beam theory

Abstract At the nanolevel, a classical continuum approach seems to be inapplicable to evaluate the mechanical behaviors of materials. With the introduction of scale parameter, the scale effect can be reasonably described by the modified continuum theory. For boron nitride nanotubes (BNNTs), the scale effect can be reflected by the curvature and the dangling bonds at both ends, mainly the former for a slender tube. This study aims to achieve a good capability of classical Euler–Bernoulli theory to directly predict the bending behaviors of single-walled BNNTs without introducing scale parameters. Elastic properties of BNNTs involving the scale effect have been first conducted by using an atomistic-continuum multiscale approach, which is directly constructed based on the atomic force field. The well-determined hexagonal boron nitride sheet is inherited in the present study of single-walled BNNTs which can be viewed as rolling up a boron nitride sheet into a seamless hollow cylinder. Euler–Bernoulli theory solution of bending deflection on the basis of the present thickness is found to be much closer to the atomistic-continuum simulation results than the commonly used interlayer space. Case studies with different tubular lengths, radii and constraints are investigated, and from which the yielded scattered scale parameters in modified continuum theories are discussed.