Multilayer Boron Nitride Research Articles

Boron Nitride‐Supported Fluorescein Isothiocyanate for Improving Optical Performance and Stability

AbstractOrganic luminogens play an indispensable role in optoelectronic devices, yet there is a pressing need to address their aggregation‐caused quenching (ACQ) and stability. Here we designed and prepared multilayered boron nitride nanosheets/fluorescein isothiocyanate (MBNNSs/FITC) composite phosphors with tunable photoluminescence by controlling the FITC content and annealing temperature. The research results indicate that MBNNSs/FITC with low or high loading of FITC is not conducive to enhancing the emission intensity of FITC, which can be attributed to the fact that low loading leads to a decrease in the content of fluorescent groups, while high loading promotes intermolecular aggregation of FITC dyes. Interestingly, the emission intensity of FITC in MBNNSs/FITC‐6 composite phosphors can be further enhanced by annealing treatment (200 °C), which can be ascribed to the suppression of the ACQ and effective energy transfer from the MBNNSs to the FITC. Moreover, the resultant composite phosphor displays outstanding thermal stability, remarkable photo stability and exceptional water‐resistance. This work provides a new design space for the development of non‐rare‐earth fluorescent materials using organic fluorescent dyes.

QRCODE: Massively parallelized real-time time-dependent density functional theory for periodic systems

We present a new software module, QRCODE (Quantum Research for Calculating Optically Driven Excitations), for massively parallelized real-time time-dependent density functional theory (RT-TDDFT) calculations of periodic systems in the open-source Qbox software package. Our approach utilizes a custom implementation of a fast Fourier transformation scheme that significantly reduces inter-node message passing interface (MPI) communication of the major computational kernel and shows impressive scaling up to 16,344 CPU cores. In addition to improving computational performance, QRCODE contains a suite of various time propagators for accurate RT-TDDFT calculations. As benchmark applications of QRCODE, we calculate the current density and optical absorption spectra of hexagonal boron nitride (h-BN) and photo-driven reaction dynamics of the ozone-oxygen reaction. We also calculate the second and higher harmonic generation of monolayer and multi-layer boron nitride structures as examples of large material systems. Our optimized implementation of RT-TDDFT in QRCODE enables large-scale calculations of real-time electron dynamics of chemical and material systems with enhanced computational performance and impressive scaling across several thousand CPU cores.

Investigating the optoelectronic characteristics of multilayer C and BN corographene using density functional theory

This study investigates the structural, optical, and electronic properties of multilayer carbon (C) and boron nitride (BN) corographene structures using first-principles calculations. The results confirm that these sheets, kept together through van der Waals forces, are energetically favorable and thermally stable. Mono-, bi-, and tri-layer C corographene sheets display semiconducting behavior, while the multilayer BN corographene sheets are insulators. Controlling the band gap can be achieved by increasing the number of layers. The optical characteristics of the sheets are anisotropic when applying electric fields polarized perpendicular or parallel to the sheets. They exhibit a high constant of static dielectric, as well as optical absorption with optical conductivity that increases according to the increase in the number of layers. The reflection and transmission constants showed that multilayer C and BN corographene sheets exhibit transparency, especially in the high-energy range. These findings suggest promising capabilities of C and BN corographene sheets for use in optoelectronic devices.

Construction of multilayered boron nitride nanosheets for improving optical performance and stability of rhodamine B

Organic fluorescent dyes have received considerable attention in optoelectronic devices. However, aggregation-caused quenching effects (ACQ) and poor stability hinder their further applications. Herein, we synthesized multilayered boron nitride nanosheets/rhodamine B (MBNNSs/RhB) composite fluorophores with intense red-light emission by adsorption process and annealing treatment. The luminescence of MBNNSs/RhB composite fluorophores can be adjusted by rational optimization of the RhB concentration and the heat-treatment temperature. Especially, the MBNNSs/RhB exhibits the strongest red emission intensity and high quantum efficiency of 88.74% after annealing treatment at 200 °C. Moreover, the composite fluorophore exhibits excellent thermal stability and luminous stability. Due to high thermal conductivity of MBNNSs, coating MBNNSs/RhB on the LED chip can effectively reduce the operating temperature of the constructed red-lighting device. This work offers many options for the development of high-performance red-emitting fluorophores.

Copper nanoparticles decorated on boron nitride nanoflakes as an efficient catalyst for the synthesis of propargylamines under green conditions

Single or multilayer boron nitride nanoflakes (BNNSs), known as white graphite, due to their have various technological applications unique properties such as mechanical stability, high thermal stability and chemical inertness. In this study, copper (Cu) nanoparticles (NPs) were successfully uniformly attached on BNSS surface by precipitation process. The morphology, composition, and chemical structure of modified BNNS were carefully identified by transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), nitrogen adsorption–desorption, elemental mapping and energy-dispersive X-ray (EDX), UV–vis absorption spectra, and atomic force microscopy (AFM). It was observed that the Cu/BNSs displayed excellent catalytic activity and recyclability for the generation of diverse propargylamines at mild conditions of three component reaction of aldehydes, amines, and alkynes. It also demonstrates that BNNSs act as efficient support to generate heterogeneous catalysts.

Electromechanical response of stacked h-BN layers: A computational study

In the current investigation, molecular dynamics simulations were performed to determine the electromechanical response of multi-layer boron nitride sheets (MLBNSs) with the consideration of different numbers of stacked layers, strain rate (SR), temperature and chirality effects, and fracture behavior subjected to uniaxial tensile tests. We found the stress–strain curves and evaluated the elastic modulus, fracture strain, and maximum tensile strength in the armchair (AC) and zigzag (ZZ) directions of BNSs. We assessed the impact of two parameters (number of stacked layers and chirality effect) on the tensile properties of BNSs by comparing the findings at various temperatures and SRs. In addition, our study reveals that MLBNSs with an odd number of BN layers show piezoelectric behavior, whereas an even number of BN layers do not show piezoelectric behavior. The piezo- and flexo-electric coefficients of MLBNSs depend on the following aspects: (i) they have an inverse relationship with the number of BN layers, (ii) even or odd numbers of BN layers, and (iii) they disappear completely when the number of BN layers exceeds ten. The present investigation motivates us to develop high-performance and lightweight piezoelectric BN-based NEMS such as nanogenerators, sensors, and actuators, as the existing piezoelectric nanomaterials are brittle, heavy, and toxic.

Ordered multilayer boron nitride nanosheets for enhancing thermal stability and optical performance of acridine orange

Organic fluorescent dyes, as non-rare-earth phosphors, are crucial in the field of optoelectronic devices but significantly impeded by inherent strong aggregation-caused quenching effects and low thermal stability. To address these problems, herein, we devise a high-performance organic-inorganic composite phosphor consisting of ordered multilayer boron nitride (BN) nanosheets as a support that simultaneously improves the optical properties and thermal stability of acridine orange (AO). Besides, the emission intensities and colors of BN/AO composite phosphors can be adjusted by controlling AO concentrations and annealing temperature. In particular, the BN/AO composite phosphor displays strong yellow-green emission after 250 °C annealing. These findings offer a new avenue for the establishment of organic-inorganic hybrid luminescent materials.

A comprehensive comparative study of the performance of carbon‐ and copper‐based interconnects in ultra‐large‐scale integrated circuits

AbstractContinuous increase of transistor count in ultra‐large‐scale integrated (ULSI) circuits demands denser interconnection networks to guarantee normal operation. As the distances between adjacent interconnect lines shrinks, severe crosstalk effects appear. New interconnect materials and technologies are proposed to alleviate deteriorating crosstalk effects and maintain overall circuit performance at a desirable level. Carbon‐based materials including carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) are among promising candidate materials to replace copper in future ULSI interconnects. In this work, carbon‐based interconnects including multiwall carbon nanotubes (MWCNTs) and multilayer graphene nanoribbons (MLGNRs), both horizontal (HMLGNRs) and vertical (VMLGNRs), are compared with traditional copper interconnects in terms of crosstalk delay and noise. Due to lower surface roughness, boron nitride (BN) is considered as substrate material for carbon‐based interconnects. To obtain more accurate and reliable results, layer number dependence of dielectric constant of BN multilayers and surface roughness dependence of the resistivity of HMLGNR interconnects are considered. The role of interconnect length, line spacing, and interlayer distance (substrate thickness) in crosstalk delay and noise of coupled carbon‐ and Cu‐based interconnect lines is investigated. It is shown that VMLGNR interconnects with perfect GNR edges exhibit the least crosstalk delay while MWCNT interconnects show far less crosstalk noise than other materials.

Structure and thermal conductivity of multi-layer Boron Nitride nano-onions medium size groupe

The structure of multilayer concentric nano-particles of boron nitride (borofen), the so-called “nano-onions” promising for creating ultra-hard sintering material, is considered. A model of the structure of hollow multilayer boron nitride nanoparticles of a medium-sized group (30 <D <100 nm, the number N of layers from 2 to 100) and an approximate estimation method for the range of changes in their effective thermal conductivity depending on the size of the nanoparticles and the number of layers are proposed

All-2D-Materials-Based Interconnects

Boron nitride (BN) multi-layers are proposed as dielectric material for both horizontal and vertical graphene nanoribbon interconnects. The layer number dependence of the out-of-plane dielectric constant of BN multi-layers is utilized to simultaneously reduce the interlayer dielectric thickness and the crosstalk delay at 7 nm CMOS technology node. Since crosstalk effects are manifested more strongly in denser interconnects, the proposed all-two-dimensional-materials-based interconnection schemes are compared with Cu/low-k technology in terms of crosstalk delay. Results show that by reducing the interlayer dielectric thickness from 20 nm to 2 nm, the crosstalk delay ratio of the horizontal and vertical graphene nanoribbon interconnects to the Cu/pSiCOH counterparts decreases by 27.06% and 12.86%, respectively. It is also shown that as the interconnect length increases, both horizontal and vertical graphene nanoribbon interconnects with the BN dielectric prove more advantageous than the Cu/low-k counterparts.

Crystal Transformation of Cubic BN Nanoislands to Rhombohedral BN Sheets on AlN for Deep-UV Light-Emitting Diodes

The large bandgap and high p-type conductivity of sp2-bonded boron nitride (BN) make the compound very attractive for deep ultraviolet light-emitting diodes (DUV LEDs). However, integrating the promising sp2 material in the DUV LED structure is challenging. This is because the reported growth conditions for scalable high-quality BN, including the high substrate temperature (>1300 °C) and the low-temperature (<1000 °C) buffer, can degrade the underneath Al-rich AlGaN quantum wells. Here, we demonstrate a wafer-scale sp2-bonded rhombohedral BN (rBN) attained on 2″ AlN/sapphire substrates by metal–organic chemical vapor deposition (MOCVD), with a single growth temperature of 1180 °C. The multilayered BN stems from three-dimensional (3D) cubic BN (cBN) nanoislands self-assembled on AlN, which then spontaneously transform into continual rBN sheets. Evidenced by high-resolution transmission electron microscopy (HRTEM), the sharp BN/AlN interface is an important step toward next-generation DUV LEDs.

First Principle Investigation of Interlayer Interaction, Stacking Order and Layer Number Dependent Structural and Electronic Properties of Multi-Layered Boron Nitride (BN)

Layered Boron-Nitride (BN) consist of covalent in-plane bonding with van der Waals (vdW) interlayer interactions between layers. In this study, stacking order, interlayer-interaction and layer number dependent structural and electronic properties of multi-layered BN were studied using Density Functional Theory (DFT). The lattice constant, equilibrium interlayer distance and energy band structures for different interlayer distances and the number of layers were computed. The calculated result indicates that interlayer interaction and stacking order in a multi-layer limit could impact on its structural and electronic properties. In addition to this, the calculated energy band structure for the increasing number of layers indicates that as the number of layers increases the bandgap decreases. However, the nature of the bandgap remains direct. Moreover, the Partial Density of State (PDOS) analysis reveals that many contributions of states in the vicinity of Fermi level derived from Boron p-orbital followed by nitrogen p-orbital. The findings are bases for experimentalist to control structural and electronic properties of layered materials by manipulating its stacking patterns and layer numbers.

Multilayer boron nitride nanofilm as an effective barrier for atomic oxygen irradiation

Boron nitride (BN) nanofilm, as a structural analogue of graphene, is one of the most promising candidates for an effective anti-oxidation barrier to protect the underlying metal. Herein, the oxidation resistance of monolayer and multilayer BN nanofilms against space atomic oxygen (AO) irradiation is studied systematically. Experimental results reveal that multilayer BN coated Cu foils exhibit superior oxidation resistance against AO irradiation than that of monolayer BN coated ones and bare Cu, resulting from the high impermeability of multilayer films. Density functional theory calculations and molecular dynamics simulations indicate that AO can be absorbed spontaneously on the surface of BN plane and can't move arbitrarily. However, AO can still damage monolayer BN film after long time irradiation, leading to the oxidation of underneath Cu. In comparison to monolayer BN, the multilayer designing of BN may adsorb AO on the top layer, and increases the diffusion difficulties of AO passing layers, which enhances the barrier performance against AO. These results prove that multilayer BN have an important promising implication as one oxidation-inhibiting barrier to anti-AO in space.

High-speed van der Waals heterostructure tunneling photodiodes integrated on silicon nitride waveguides

Graphene photodetectors can have broadband operation and a large bandwidth, but they usually suffer from a large dark current when biased. To solve this problem, we demonstrate van der Waals heterostructure tunneling photodiodes integrated on silicon nitride waveguides. The heterostructure is made up of layers of molybdenum disulfide, graphene, boron nitride, and graphene from bottom to top. The bottom graphene is n-doped by molybdenum disulfide while the top graphene layer remains p-doped. Between the two graphene layers, multilayer boron nitride was employed as a tunneling barrier. At ∼1550 nm, high on/off current ratios larger than 104 were measured in the dark. A responsivity of ∼0.24 A/W and a bandwidth of 28 GHz (56 GHz by deconvolving response of experimental system) were also obtained.

Length-dependent lattice thermal conductivity of single-layer and multilayer hexagonal boron nitride: A first-principles study using the Callaway-Klemens and real-space supercell methods

The phonon dispersion, density of states, Gr\"{u}neisen parameters, and the lattice thermal conductivity of single- and multi-layered boron nitride were calculated using first-principles methods. For the bulk {\it h}-BN we also report the two-phonon density of states. We also present simple analytical solutions to the acoustic vibrational mode-dependent lattice thermal conductivity. Moreover, computations based on the elaborate Callaway-Klemens and the real space super cell methods are presented to calculate the sample length and temperature dependent lattice thermal conductivity of single- and multi-layered hexagonal boron nitride which shows good agreement with experimental data.

Molecular Dynamics Simulation of Water Transport Mechanisms through Nanoporous Boron Nitride and Graphene Multilayers.

In this study, molecular dynamics simulations are used to investigate water transport mechanisms through hourglass-shaped pore structure in nanoporous boron nitride (BN) and graphene multilayers. An increase in water flux is evidenced as the gap between the layers increases, reaching a maximum of 41 and 43 ns-1 at d = 6 Å in BN and graphene multilayers, respectively. Moreover, the BN multilayer exhibits less flux compared to graphene due to large friction force and energy barrier. In BN, the friction force dramatically increases when the layers are strongly stacked (d = 3.5 Å), whereas it would be independent of the layer separation when the layers are sufficiently spaced (d ≥ 5 Å). In contrast, it was shown that the friction force is independent of the layer spacing in graphene. On the other hand, water molecules across the BN exhibits larger energy barriers compared to graphene when the layers are highly spaced at d = 8 Å. Consistent with the result reported for the flux, the axial diffusion coefficient of water molecules in graphene increases with layer spacing, reaching a maximum of 6.8 × 10-5 cm2/s when the layers are spaced at d = 6 Å.

Influence of bias on the electronic structure and electrical conductivity and heat capacity of graphene and boron nitride multilayers

The electronic structure, electrical conductivity, heat capacity and thermal conductivity of BN and BN/graphene/BN with three and five layers are investigated using the tight binding approximation and Green's function method. The BN/graphene/BN trilayers show narrow band gap unlike to BN trilayers where which have wide band gap. The energy gap of BN trilayers decreases linearly with electric field unlike to the BN/graphene/BN trilayers. The magnitude of changes in the band gap for BN trilayers are much higher than the BN/graphene/BN trilayers. The electrical conductivity, heat capacity and thermal conductivity are zero for BN trilayers and it increases with temperature until reaches maximum value then decreases. The electrical conductivity of BN/graphene bilayers is larger than BN bilayers. For all cases, the heat capacity has a Schottky anomalies.

Physics behind Water Transport through Nanoporous Boron Nitride and Graphene.

In this work, molecular dynamics simulations were used to determine the surface tension profile of water on graphene and boron nitride (BN) multilayers and to predict water permeation through nanoporous graphene and BN membranes. For both graphene and BN multilayers, a decrease in surface tension (γ) was evidenced as the number of layers increased. This lessening in γ was shown to result from a negative surface tension contribution due to long-range wetting of water, which also contributes to lower water permeation through a two-layer membrane with respect to permeation through a monolayer. We also showed that a decrease in water surface tension on a BN monolayer with regards to graphene was at the origin of an increase in water permeation through BN. Our findings suggest that nanoporous BN membranes could be attractive candidates for desalination applications.

Noise and sensitivity characteristics of solid-state nanopores with a boron nitride 2-D membrane on a pyrex substrate.

We have fabricated highly sensitive and low noise solid-state nanopores with multiple layers of boron nitride (BN) membranes transferred onto a pyrex substrate. Both the dielectric and flicker noise of the device, which have been described as one of the bottlenecks to making highly sensitive 2-D membrane nanopore devices, have been reduced as follows. Firstly, a pyrex substrate with a low dielectric constant (εr = 4.7-5.1) and low dielectric loss (D < 0.001) is used instead of a Si substrate to reduce the dielectric noise of the device. Secondly, flicker noise is minimized by employing a 100 nm thick SiNx supporting layer with a small opening (less than 100 nm) for BN membrane transfer to enhance the mechanical stability. The flicker noise is further reduced by transferring multiple layers of BN instead of a single layer of BN. The resulting multi-layered BN device shows significant reduction of dielectric and 1/f noise as compared to the devices with a single layer of the BN and Si substrate. Furthermore, we demonstrate dsDNA translocations with a high signal to noise ratio around 50 at 100 and 10 kHz bandwidths.

Communication—Multi-Layer Boron Nitride Nanosheets as Corrosion-Protective Coating Fillers

Boron nitride nanosheets (BNNSs) have many outstanding properties for corrosion protection. Herein, multi-layer BNNSs are synthesized by a liquid-exfoliation method and serve as highly-effective nanofillers for polyvinyl butyral (PVB) coatings. Electrochemical characterizations reveal that the corrosion rate of copper protected by BNNSs/PVB composite coating is 5 orders of magnitude lower than that protected by pristine PVB coating. Raman spectra show no corrosion products formed on copper beneath PVB coating which is reinforced with more than 0.5 wt% BNNSs. We believe this study opens a new avenue for developing highly-impermeable polymeric composites for corrosion protection.