Boron Nitride Membranes Research Articles

Mechanical properties of [formula omitted]-bonded carbon and boron nitride 2D membranes: A first principles study

Transverse compression and chemical passivation of few graphene or hexagonal boron nitride layers have been shown to be viable means to form ultrathin membranes rich in sp3 bonds exhibiting intriguing mechanical behaviors. Here, density functional theory calculations are used to calculate second- and third-order elastic constants, as well as ideal breaking strengths of both layered and sp3-bonded arbon and boron nitride films. The sp3-bonded membranes consist of two or three planes of both existing and new in silico-designed bulk structures of carbon and boron nitride, and have either both, one, or none of the surfaces passivated with hydrogen. This study shows that carbon and boron nitride membranes rich in sp3 bonds exhibit mechanical properties and ideal breaking strengths that compete with those of sp2-bonded layered films, and that there is a plethora of plausible stable structures of such sp3-bonded membranes, showing diverse electronic properties, and longitudinal and transverse mechanical behaviors. This study also suggests that by controlling thickness of the film and by tuning chemistry of the supporting substrate, transverse compression of layered carbon or hexagonal boron nitride films could lead to the formation of stable sp3-bonded 2D materials exposing clean surfaces, and therefore transferable, and exhibiting intriguing anisotropic mechanical and electronic properties.

Proton conductivity of a hexagonal boron nitride membrane and its energy applications

The excellent proton conductivity of h-BN and its applications.

Ultrafast, Stable Ionic and Molecular Sieving through Functionalized Boron Nitride Membranes.

Porous membranes play an important role in the separation technologies such as gas purification, solute nanofiltration, and desalination. An ideal membrane should be thin to maximize permeation speed, have optimum pore sizes to maximize selectivity, and be stable in various harsh conditions. Here, we show that the nanometer-thick membrane prepared by means of filtration of functionalized boron nitride (FBN) water suspensions can block solutes with hydrated radii larger than 4.3 Å in water. The FBN membranes with abundant nanochannels reduce the path length of ions. As molecular sieves, the FBN membrane can permeate small ions at an ultrahigh rate-a 25-fold enhancement compared with that of its theoretical diffusion rate and much higher than the graphene oxide membrane. Importantly, the FBN membrane exhibits excellent permeability even when it is immersed in acidic, alkaline, and basic salts solutions because of its intrinsic chemical stability. The molecular dynamics simulations further confirmed that the nanocapillaries formed within the FBN membrane in the hydrated state were responsible for high permeation performance. The simple vacuum filtration fabricated FBN membrane with angstrom-sized channels and ultrafast permeation of ions promises great potential applications in the areas of barrier separation and water purification.

Nanoporous Boron Nitride Membranes for Helium Separation

Porous boron nitride (BN) membranes PBN-BH, PBN-BNH, and PBN-NH were designed as promising membranes for purifying He from natural gas by using density functional theory. The three BN membranes wer...

Analog quantum simulation of extremely sub-Ohmic spin-boson models

We propose a scheme for the quantum simulation of sub-Ohmic spin--boson models by color centers in free-standing hexagonal boron nitride (h-BN) membranes. The electronic spin of a color center that couples to the membrane vibrational spectrum constitute the physical model. The spin-motion coupling is provided by an external magnetic field gradient. In this study, we show that a class of spectral densities can be attained by engineering geometry and boundary conditions of the h-BN resonator. We then put our focus on two extreme cases, i.e. $1/f$- and white-noise spectral densities. Spin coherence and polarization dynamics are studied. Our calculations show coherence revivals at periods set by the bath characteristic frequency signaling the non-Markovian nature of the baths. The nonequilibrium dynamics of the spin polarization exhibits a coherent localization, a property peculiar to the quantum phase transition in extremely sub-Ohmic spin-boson models. Our scheme may find application in understanding sources of decoherence in solid-state quantum bits.

Functionalized boron nitride membranes with ultrafast solvent transport performance for molecular separation

Pressure-driven, superfast organic solvent filtration membranes have significant practical applications. An excellent filtration membrane should exhibit high selectivity and permeation in aqueous and organic solvents to meet increasing industrial demand. Here, we report an amino functionalized boron nitride (FBN) based filtration membrane with a nanochannel network for molecular separation and permeation. This membrane is highly stable in water and in several organic solvents and shows high transport performance for solvents depending on the membranes’ thickness. In addition, the FBN membrane is applicable for solute screening in water as well as in organic solvents. More importantly, the FBN membranes are very stable in acidic, alkaline and oxidative media for up to one month. The fast-flow rate and good separation performance of the FBN membranes can be attributed to their stable networks of nanochannels and thin laminar structure, which provide the membranes with beneficial properties for practical separation and purification processes.

Nanofluidic electric generators constructed from boron nitride nanosheet membranes

Harvesting clean energy through artificial devices has attracted tremendous interest in the past few decades. More specifically, electricity generated by electrokinetic effects has received much attention recently due to the development of microfluidic and nanofluidic device. In this paper, we have developed a novel power-generating device based on membranes made of boron nitride (BN) nanosheets. The hydrated BN membrane contains intra-layer spacing between individual BN nanosheets, which can form nanofluidic channels to accommodate water molecules and ions. This novel device with a membrane area of 5 mm2 generates a large current of 12.1 nA in 0.1 M NaCl solution with a pressure gradient of 5 kPa, and reaching a maximum output power of 3.2 pW. Furthermore, multiple devices can be connected and operated simultaneously to increase the current output, which is promising for future clean energy harvesting devices.

Structural transformations of carbon and boron nitride nanoscrolls at high impact collisions.

The behavior of nanostructures under high strain-rate conditions has been the object of theoretical and experimental investigations in recent years. For instance, it has been shown that carbon and boron nitride nanotubes can be unzipped into nanoribbons at high-velocity impacts. However, the response of many nanostructures to high strain-rate conditions is still unknown. In this work, we have investigated the mechanical behavior of carbon (CNS) and boron nitride nanoscrolls (BNS) colliding against solid targets at high velocities, using fully atomistic reactive (ReaxFF) molecular dynamics (MD) simulations. CNS (BNS) are graphene (boron nitride) membranes rolled up into papyrus-like structures. Their open-ended topology leads to unique properties not found in their close-ended analogs, such as nanotubes. Our results show that collision products are mainly determined by impact velocities and by two orientation angles, which define the position of the scroll (i) axis and (ii) open edge relative to the target. Our MD results showed that for appropriate velocities and orientations, large-scale deformations and nanoscroll fractures could occur. We also observed unscrolling (scrolls going back to quasi-planar membranes), scroll unzipping into nanoribbons, and significant reconstruction due to breaking and/or formation of new chemical bonds. For particular edge orientations and velocities, conversion from open to close-ended topology is also possible, due to the fusion of nanoscroll walls.

Functionalized boron nitride membranes with multipurpose and super-stable semi-permeability in solvents

Multipurpose and super-stable molecular sieving membranes exhibit great potential for mixture separation at low energy cost within extreme chemical and thermal environments.

Spin-Mechanical Scheme with Color Centers in Hexagonal Boron Nitride Membranes.

Recently observed quantum emitters in hexagonal boron nitride (hBN) membranes have a potential for achieving high accessibility and controllability thanks to the lower spatial dimension. Moreover, these objects naturally have a high sensitivity to vibrations of the hosting membrane due to its low mass density and high elasticity modulus. Here, we propose and analyze a spin-mechanical system based on color centers in a suspended hBN mechanical resonator. Through group theoretical analyses and abinitio calculation of the electronic and spin properties of such a system, we identify a spin doublet ground state and demonstrate that a spin-motion interaction can be engineered, which enables ground-state cooling of the mechanical resonator. We also present a toolbox for initialization, rotation, and readout of the defect spin qubit. As a result, the proposed setup presents the possibility for studying a wide range of physics. To illustrate its assets, we show that a fast and noise-resilient preparation of a multicomponent cat state and a squeezed state of the mechanical resonator is possible; the latter is achieved by realizing the extremely detuned, ultrastrong coupling regime of the Rabi model, where a phonon superradiant phase transition is expected to occur.

High and Stable Ionic Conductivity in 2D Nanofluidic Ion Channels between Boron Nitride Layers.

Achieving a high rate of ionic transport through porous membranes and ionic channels is important in numerous applications ranging from energy storage to water desalination, but it still remains a challenge. Herein we show that ions can quickly pass through interlayer spaces in hydrated boron nitride (BN) membranes. Measurements of surface-charge governed ionic currents between BN nanosheets in a variety of salt solutions (KCl, NaCl and CaCl2) at low salt concentrations (<10-4 M) showed several orders of magnitude higher ionic conductivity compared to that of the bulk solution. Moreover, due to the outstanding chemical and thermal stability of BN, the ionic conduits remain fully functional at temperatures up to 90 °C. The BN conduits can operate in acidic and basic environments and do not degrade after immersing in solutions with extreme pH (pH ∼ 0 or 14) for 1 week. Those excellent properties make the BN ionic conduits attractive for applications in nanofluidic devices and membrane separation.

Flexible metal-semiconductor-metal device prototype on wafer-scale thick boron nitride layers grown by MOVPE

Practical boron nitride (BN) detector applications will require uniform materials over large surface area and thick BN layers. To report important progress toward these technological requirements, 1~2.5 µm-thick BN layers were grown on 2-inch sapphire substrates by metal-organic vapor phase epitaxy (MOVPE). The structural and optical properties were carefully characterized and discussed. The thick layers exhibited strong band-edge absorption near 215 nm. A highly oriented two-dimensional h-BN structure was formed at the film/sapphire interface, which permitted an effective exfoliation of the thick BN film onto other adhesive supports. And this structure resulted in a metal-semiconductor-metal (MSM) device prototype fabricated on BN membrane delaminating from the substrate. MSM photodiode prototype showed low dark current of 2 nA under 100 V, and 100 ± 20% photoconductivity yield for deep UV light illumination. These wafer-scale MOVPE-grown thick BN layers present great potential for the development of deep UV photodetection applications, and even for flexible (opto-) electronics in the future.

Hydrogen purification performance of a nanoporous hexagonal boron nitride membrane: molecular dynamics and first-principle simulations.

Membranes have attracted much attention for the efficient separation of gas mixtures, due to their specific structural and unique properties. In this work, density functional theory (DFT) and molecular dynamic (MD) simulations have been employed to evaluate the performance of nanoporous hexagonal boron nitride (h-BN) monolayers for hydrogen purification. Various porous membranes were designed, and full structural relaxation was carried out by using DFT calculations and then MD simulations to investigate the H2 purification performance of the nanoporous h-BN membranes. It was found that the selectivity for H2 gas over N2 gas was highly sensitive to the type and width of the pores. The h-BN membrane containing pores with short and long sides both of about 3 Å (pore 1B-3N) demonstrated optimal selectivity for H2 molecules, while the permeability of the pore 5B-5N + 4H membrane (short side of about 4.4 Å) was much higher than that of other counterparts. Furthermore, DFT calculations were performed to validate the MD simulation observations as well as to explain the selectivity performance of the most desirable pore membrane. We demonstrated that the 1B-3N pore is a far superior membrane to other counterparts and exhibits an excellent potential for applications in hydrogen purification, clean energy combustion, and the design of novel membranes for gas separation.

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.

Violation of the universal behavior of membranes inside cylindrical tubes at nanoscale

Recently, it was proposed based on classical elasticity theory and experiments at macroscale, that the conformations of sheets inside cylindrical tubes present a universal behavior. A natural question is whether this behavior still holds at nanoscale. Based on molecular-dynamics simulations and analytical modeling for graphene and boron nitride membranes confined inside carbon nanotubes, we show that the class of universality observed at macroscale is violated at nanoscale. The precise origin of these discrepancies is addressed and proven to be related to both surface and atomistic effects.

Boron-nitride nanotube triggered self-assembly of hexagonal boron-nitride nanostructure

Molecular mechanics results show that a hexagonal boron nitride (h-BN) membrane can spontaneously assemble on the single-walled boron nitride nanotube (BNNT) in a scroll or helical manner, showing an interesting dependence on h-BN width. The size of BNNTs should meet the required conditions to guarantee self-assembly. Further analyses of energy components and structural geometry show that this unique phenomenon is because of the combined action of van der Waals interactions and the π-π stacking effect. The h-BNs with arbitrary sizes and shapes can wrap onto BNNTs to form various configurations. The self-assembly conditions and the stability of the formed nanoconfigurations are investigated for numerous potential applications.

Controlling Bandgap of Rippled Hexagonal Boron Nitride Membranes via Plasma Treatment

Few-layer rippled hexagonal boron nitride (h-BN) membranes were processed with hydrogen plasma, which exhibit distinct and pronounced changes in its electronic properties after the plasma treatment. The bandgaps of the h-BN membrane reduced from ~5.6 eV at 0 s to ~4.25 eV at 250 s, which is a signature of transition from the insulating to the semiconductive regime. It typically required 250 s of plasma treatment to reach the saturation. It illustrates that two-dimensional material with engineered electronic properties can be created by attaching other atoms or molecules.

Tribological Properties of Graphene and Boron-Nitride Layers: A Fully Atomistic Molecular Dynamics Study

ABSTRACTGraphene has been one of the most important subjects in materials science in the last years. Recently, the frictional characteristics of atomically thin sheets were experimentally investigated using atomic force microscopy (AFM). A new mechanism to explain the enhanced friction for these materials, based on elastic compliance has been proposed. Here, we have investigated the tribological properties of graphene and boron-nitride (single and multi-layers) membranes using fully atomistic molecular dynamics simulations. These simulations were carried out using classical force fields, as implemented in the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code. The used structural models contain typically hundreds of thousands of atoms. In order to mimic the experimental conditions, an artificial AFM tip was moved over the membranes and the tribological characteristics determined in terms of forces and energies. Our results are in good agreement with the available experimental data. They show that the observed enhanced tribological properties can be explained in terms of out-of-plane geometrical distortions and elastic waves propagation. They validate the general features of the model proposed by Lee et al. (Science 328, 76 (2010).

Controlled Radiation Damage and Edge Structures in Boron Nitride Membranes

We show that hexagonal boron nitride membranes synthesized by chemical exfoliation are more resistant to electron beam irradiation at 80 kV than is graphene, consistent with quantum chemical calculations describing the radiation damage processes. Monolayer hexagonal boron nitride does not form vacancy defects or amorphize during extended electron beam irradiation. Zigzag edge structures are predominant in thin membranes for both a freestanding boron nitride monolayer and for a supported multilayer step edge. We have also determined that the elemental termination species in the zigzag edges is predominantly N.