BN Monolayer Research Articles

Quantum valley Hall effect in wide-gap semiconductor SiC monolayer

We have investigated the valley Chern number and gapless edge states in wide-gap semiconductor SiC and BN monolayers by using the density functional theory calculations. We found that while SiC monolayer has a non-quantized valley Chern number due to a partial mixing of the Berry curvature peaks pertaining to the opposite valleys, there exist topologically protected gapless edge states within the bulk gap, leading to a quantum valley Hall effect. Doping of the opposite charge carriers causes a backscattering-free valley current flowing on the opposite edge, which can be used for experimental confirmation and application at room temperature. BN monolayer, on the other hand, was found to have gapped edge states due to the too large staggered AB-sublattice potentials.

Gas Sensing Performance of Pristine and Monovacant C6BN Monolayers Evaluated by Density Functional Theory and the Nonequilibrium Green’s Function Formalism

The application potential of pristine and monovacant C6BN for sensing gaseous pollutants (CO, CO2, NO, NO2, NH3, H2S, and SO2) is investigated using density functional theory with van der Waals dis...

Electro-Optical Properties of Monolayer and Bilayer Pentagonal BN: First Principles Study.

Two-dimensional hexagonal boron nitride (hBN) is an insulator with polar covalent B-N bonds. Monolayer and bilayer pentagonal BN emerge as an optoelectronic material, which can be used in photo-based devices such as photodetectors and photocatalysis. Herein, we implement spin polarized electron density calculations to extract electronic/optical properties of mono- and bilayer pentagonal BN structures, labeled as , , and . Unlike the insulating hBN, the pentagonal BN exhibits metallic or semiconducting behavior, depending on the detailed pentagonal structures. The origin of the metallicity is attributed to the delocalized boron (B) 2p electrons, which has been verified by electron localized function and electronic band structure as well as density of states. Interestingly, all 3D networks of different bilayer pentagonal BN are dynamically stable unlike 2D structures, whose monolayer is unstable. These 3D materials retain their metallic and semiconductor nature. Our findings of the optical properties indicate that pentagonal BN has a visible absorption peak that is suitable for photovoltaic application. Metallic behavior of pentagonal BN has a particular potential for thin-film based devices and nanomaterial engineering.

Si2BN monolayers as promising candidates for hydrogen storage.

Hydrogen storage properties of the pure Si2BN monolayer were studied using density functional theory calculations. The interaction of H2 molecules with the Si2BN monolayer is weak and of electrostatic nature. The average hydrogen adsorption energies are within the ideal range of practical applications (0.187-0.214 eV), and the consecutive adsorption energies indicate that the spontaneous adsorption of H2 molecules on the Si2BN monolayer can occur. The hydrogen gravimetric density of the periodic Si2BN monolayer reaches 8.5 wt%, which exceeds the standard of 6.0 wt% set by the US Department of Energy (DOE) by the year 2020. The estimated desorption temperatures show the desirable properties for the long term recycling of the Si2BN storage medium. Thus, our results show that the Si2BN monolayer is a promising candidate for molecular hydrogen storage.

Hidden porous boron nitride as a high-efficiency membrane for hydrogen purification.

Nanoporous atom-thick two-dimensional materials with uniform pore size distribution and excellent mechanical strength have been considered as the ideal membranes for hydrogen purification. Here, our first-principles structure search has unravelled four porous boron nitride monolayers (m-BN, t-BN, h'-BN and h''-BN) that are metastable relative to h-BN. Especially, h'-BN consisting of B6N6 rings exhibits outstanding selectivity and permeability for hydrogen purification, higher than those of common membranes. Importantly, h'-BN possesses the mechanical strength to sustain a stress of 48 GPa, which is two orders of magnitude higher than that (0.38 GPa) of a recently reported graphene-nanomesh/single-walled carbon nanotube network hybrid membrane. The excellent selectivity, permeability and mechanical strength make h'-BN an ideal candidate for hydrogen purification.

Theoretical screening of efficient single-atom catalysts for nitrogen fixation based on a defective BN monolayer.

The electrocatalytic reduction of naturally abundant N2 to NH3 is an attractive approach to replace the Haber-Bosch nitrogen-fixation process that causes enormous energy consumption and greenhouse gas emissions. However, designing high-performance catalysts toward the electrocatalytic N2 reduction reaction (eNRR) remains one of the greatest challenges in this area. Herein, high-throughput screening of catalysts for the NRR among a series of transition metal atoms supported on a defective hexagonal boron nitride (h-BN) nanosheet is performed through spin-polarized density functional theory (DFT) computations. Strikingly, among the 18 candidates, the V/Tc atom anchored on a defective h-BN monolayer (V@BN and Tc@BN) showed good NRR activity with relatively low onset potentials. Particularly, V@BN was found to exhibit outstanding catalytic activity for the NRR via an enzymatic pathway with an extremely low overpotential of 0.25 V. The value is significantly lower than that on the Ru (0001) stepped surface that has the best NRR catalytic performance among bulk metal catalysts. The novel NRR activity of V@BN is attributed to the enhanced electrical conductivity due to V-doping, the "donation-backdonation" process for N2 activation, and the highly centralized spin-polarization on the V atom. This work not only provides a quite promising catalyst for the NRR but also provides new insights for the rational design of single-atom NRR catalysts.

Emergence of Si2BN Monolayer as Efficient HER Catalyst under Co-functionalization Influence

In the present work, we have envisaged the enhancement of hydrogen evolution reaction (HER) activity on stable Si2BN monolayer based on first-principles electronic structure calculations. Herein, w ...

Molecular dynamics study of pristine and defective hexagonal BN, SiC and SiGe monolayers

The structural and thermodynamical properties of 2D honeycomb hybrids are investigated over a wide temperatures range by carrying out atomistic simulations using Tersoff-type interatomic empirical potential. The variance of the radial distribution as well as the height correlation functions in terms of temperature and buckling parameter are discussed for the SiC, SiGe and BN compounds. A non-monotonic growth of mean square displacement is observed when increasing the defect concentration. The energetic of Stone–Wales defects and vacancies as well as the magnitude of thermally excited ripples for both pristine and defective monolayers increase significantly at higher temperatures, which is caused by the increase in bond lengths and atom’s velocities, resulting in higher kinetic energy. It follows that thermal rippling is intricately related to thermal expansion.

Electronic and optical properties of Ge doped graphene and BN monolayers

The effect of germanium doping on the properties of hexagonal boron nitride and graphene monolayers was investigated using ab initio calculations. For boron nitride, the obtained results indicate the formation of electronic states in the region of the gap, near the Fermi level. The incorporation of such impurity atoms also induces an apparent decrease in the energy gap and a significant reduction in the optical conductivity. The calculations indicate small absorbance for wavelengths from infrared to visible light. For the graphene layer, it has been obtained a null gap semi-metal material. This result can be associated with the corresponding displacement of the Fermi level. In addition, the germanium doped graphene shows similar optical properties when compared with the pristine layer.

Formation of hBN monolayers through nitridation of epitaxial silicene on diboride thin films

The formation process of hexagonal boron nitride (hBN) monolayer sheets on single-crystalline ZrB2(0001) thin films grown on Si(111) wafers has been investigated by electron diffraction, scanning tunneling microscopy, and photoelectron spectroscopy. A two-step reaction was identified, resulting first in the formation of a silicon nitride layer by room temperature exposure of the silicene-terminated ZrB2 thin film surface to nitrogen radicals and then in the formation of an hBN monolayer replacing the silicon nitride layer through annealing at 900 °C. A large-scale moiré pattern and a clear dispersion of the π-electronic band provide evidence for the formation of an epitaxial hBN monolayer sheet directly on the diboride surface. The unique ability of the ZrB2(0001) surface, upon which both silicene and hBN monolayers can be formed, opens a way toward the integration of these two very different two-dimensional materials.

First-principles studies of graphene antidot lattices on monolayer h-BN substrate

The structures and electronic structures of hetero bilayers composed of graphene antidot lattice (GAL) on monolayer h-BN substrate are studied in first-principles method. Bond lengths, interlayer distances, flatness, biaxial strain effects, and effects of translating the GAL layer are studied and analyzed in detail. Results show that introducing a monolayer BN substrate makes the zero-bandgap 5×5 GAL open a bandgap up to 28 meV, while it makes the semiconducting 6×6 GAL keep its low-energy electronic structure almost intact except a small bandgap change by tens of meV at most. Our studies demonstrate that h-BN is a promising substrate for GAL.

Theoretical investigation on the structures, electronic and magnetic properties of new 2D/1D composite nanosystems by adsorbing superhalogen MnCl3 on the BN monolayer/nanoribbons

Hexagonal boron nitride (h-BN), an inorganic analogue of graphene, possesses the remarkable physical and chemical properties and can be viewed as the powerful building block to construct novel composite nanomaterials. In this study, based on the first-principles calculations, we design a new class of hybrid nanosystems by depositing superhalogen MnCl3 on the surface of low-dimensional BN monolayer or nanoribbons (BNML/BNNRs). The large adsorption energies indicate that the MnCl3 can be stably adsorbed on the surface of the BN materials. Regardless of dimension, chirality, ribbon width as well as the adsorption site and coverage of MnCl3, adsorbing MnCl3 can endow these hybrid BN nanomaterials with a large magnetic moment and significantly reduce the robust wide band gap of BN materials to the range of 0.098–0.948 eV. Overall, these new MnCl3–BN composite nanostructures can display the large magnetism and an appropriate band gap, which is very promising to make them an application in the field of multifunctional nanodevices and magnetic materials in the near future.

Protection of one-dimensional Si chains embedded in Pt(111) and protected by a hexagonal boron-nitride monolayer

Using scanning tunneling microscopy, we study the regime of submonolayer Si deposition on Pt(111) at 300 K. We find a novel network of one-dimensional chains embedded into the Pt surface. Even in ultrahigh vacuum, these chains disappear within a few hours in favor of clusters on top of the Pt surface. Exposing the chains to different gases reveals that CO effectively induces the lifting. However, the Si chains can be protected by a monolayer of hexagonal BN (h-BN) deposited prior to the Si deposition. Then, the chains survive even an exposure for ten min to air. Interestingly, the Si chains below the h-BN are rotated by 30∘ with respect to the ones on the bare Pt(111). This might be related to the anisotropic elastic modulus of the h-BN on top.

Monolayer and thin h–BN as substrates for electron spectro-microscopy analysis of plasmonic nanoparticles

The influence of four substrates [thin Si3N4, few-layer graphene (FLG), thin h–BN, and monolayer h–BN] on plasmon resonances of metallic nanoparticles was studied using electron energy loss spectroscopy. The h–BN monolayer is an excellent substrate for the study of plasmonic particles due to its large bandgap, negligible charging under electron irradiation, and negligible influence on the plasmon resonance full width at half maximum and peak positions. These effects were evidenced in experiments with gold nanotriangles focusing on dipolar modes. Nanotriangles on h–BN exhibit the lowest influence from the substrate compared to Si3N4 and FLG. In a dataset containing 23 triangles of similar sizes, the dipolar mode was found to have smaller redshifts, sharper peak widths, and higher resonance quality factors on h–BN, showing that it has nearly no effect on the plasmon absorption properties, provided that it is free from carbon contamination. However, light emission (cathodoluminescence) decreases as a function of electron irradiation for triangles on h–BN, even though the electron energy loss signal stays unchanged. This indicates the creation of non-radiative decay channels.

Site- and spin-dependent coupling at the highly ordered h -BN/Co(0001) interface

L.V.Ya. acknowledges the RSF (Grant No. 16-42-01093). A.V.T., V.O.S., K.A.B., O.Yu.V., and D.Yu.U. acknowledge St. Petersburg State University for research Grant No. 11.65.42.2017. M.V.K. and I.I.O. acknowledge the RFBR (Grant No. 16-29-06410). C.L. acknowledges the DFG (Grant Nos. LA655-17/1 and LA655-19/1).

Understanding wetting at nano scale: Atomistic simulation investigations

The wetting property of water is crucial in a variety of chemical, biological and technological systems. Finding the relevance between water and the structure of material surface is the key to understand the wettability of water and other implications such as those design nanostructured devices. In those work, we attempt to use the classical and the first-principles molecular dynamics simulations to explore the interactions between water and material surfaces. We have achieved a series of results, mainly including the following aspects: (1) Wettability of graphene and h-BN. (2) Relations between wettability and lattice constant. (3) Wetting of synthesized Bi2Se3. The water contact angle of the ideal Bi2Se3 surface is ~98.4°, and the edge of the terrace on its surface is extremely hydrophilic. (4) Wenzel to Cassie state transition. (5) Characterizing hydrophobicities of amino acid side chains. (6) Hydrophobicity and ion-selectivity. According to these examples, it is found that the molecular dynamics simulation is an extremely important tool to reveal the mechanism of wetting. In wettability of graphene and h-BN, we used Born-Oppenheim quantum molecular dynamics (QMD) simulations and investigated interfacial properties of water droplets on a graphene sheet or a monolayer BN sheet. The QMD simulations reveal that the contact angle of the graphene is 87°, while the contact angle of the monolayer BN sheet is 86°. So they all show weakly hydrophobic. Compared with nanodroplets of water in a supercooled state on the graphene, the results show that under the supercooled condition, water droplets exhibit an appreciably larger contact angle than under the ambient condition. In addition, there are also related introductions about evolution of the interfacial shape in dissolutive wetting and electrowetting. In the relations between wettability and lattice constant, the MD simulation presents a small uniform strain (±3%) applied to the lattice constant of a multilayer hydrophilic surface can generate a marked change in the wetting tendency. Meanwhile, when the lattice constant of a hydrophilic surface matches the projected oxygen-oxygen distance of bulk water to the surface, a contact-angle minimum is resulted. They surmised that the structure of the first water layer next to the surface can strongly affect the contact angle of water droplets. For vdW layered materials surface and nanostructured surfaces by design, the MD simulations show that a modified Wenzel model can proposed for describing the wetting behavior of van der Waals layered materials with topographic surfaces and the water contact angle of the ideal Bi2Se3 surface is ~98.4°. The Cassie state may translate into Wenzel state via precisely designed trapezoidal nanostructures. Two key parameters—The base angle of the trapezoids and the intrinsic contact angle—can be controlled the transition. For example, there will be three regimes for a given base angle. For characterizing hydrophobicity of amino acid side chains in a protein environment, the hydrophobicity of 20 types of amino acids has been studied by measuring the CA ( θ ) of a water nanodroplet. The results show that all nonpolar amino acid side chains are hydrophobic and the difference in θ among the nonpolar amino acid side chains is very small. Finally, we introduced the mechanism of selective ion transport in hydrophobic subnanometer channels, intercalation and diffusion of lithium inos in a carbon nanotube bundle and a series of related issues.

A DFT Study of Single‐Atom Catalysis of CO Oxidation Using Carbon‐Embedded Hexagonal Boron Nitride Monolayer

AbstractThe catalytic oxidation of CO by O2 molecule under mild conditions is one of the attractive processes in chemistry and industry. In the present study, by means of periodic density functional theory calculations, the potential of experimentally available carbon‐doped hexagonal boron nitride (h‐BN) nanosheets as a metal‐free catalyst for the CO oxidation is investigated. It is found that C‐doping induces high spin density into BN monolayer which is mainly localized over the C and its neighboring N or B atoms. Both Langmuir–Hinshelwood (LH) and Eley–Rideal (ER) mechanisms are considered for the CO oxidation reaction. The calculated reaction barriers reveal that the CO oxidation proceeds first via the LH mechanism CO + O2 → OCOO → CO2 + O* and then via the ER mechanism CO + O* → OCO* → CO2. Our results suggest that the CO oxidation catalyzed by the C‐doped h‐BN sheets is likely to occur at the normal condition.

Carbon-doped boron nitride nanosheet as a promising catalyst for N2O reduction by CO or SO2 molecule: A comparative DFT study

We report for the first time, the catalytic activity of the experimentally available carbon-doped boron nitride nanosheet (C-BNNS) towards the reduction of N2O in the presence of CO or SO2 molecule. According to our density functional theory calculations, C-doping can introduce high spin density into BN monolayer which is mainly localized over the C and its neighboring N atoms. The Hirshfeld charge density analysis reveals that the electron-rich C-BNNS acts as an electron donating support to activate N2O molecule which is an important step in the reduction of N2O. The N2O reduction reaction starts with the dissociative adsorption of N2O over the C-BNNS surface, yielding the N2 molecule and an activated oxygen moiety (Oads) adsorbed over the C atom. The reaction then proceeds via the elimination of Oads by a CO or SO2 molecule. The obtained low activation energies clearly indicate that the metal-free C-BNNS surface can be regarded as a highly active catalyst for the reduction of N2O. The results of this study may open new avenues in searching low cost and highly active BN-based catalysts for low temperature reduction of N2O.

Modulation of band gap by an applied electric field in BN-based heterostructures

First-principles density functional theory (DFT) calculations are performed on the structural and electronic properties of the SiC/BN van der Waals (vdW) heterostructures under an external electric field (E-field). Our results reveal that the SiC/BN vdW heterostructure has a direct band gap of 2.41 eV in the raw. The results also imply that electrons are likely to transfer from BN to SiC monolayer due to the deeper potential of BN monolayer. It is also observed that, by applying an E-field, ranging from −0.50 to +0.65 V/Å, the band gap decreases from 2.41 eV to zero, which presents a parabola-like relationship around 0.0 V/Å. Through partial density of states (PDOS) plots, it is revealed that, p orbital of Si, C, B, and N atoms are responsible for the significant variations of band gap. These obtained results predict that, the electric field tunable band gap of the SiC/BN vdW heterostructures carries potential applications for nanoelectronics and spintronic device applications.

Polarity-Induced Surface Recognition and Self-Assembly of Noncanonical DNA Nucleobases on h-BN Monolayer

A systematic understanding of the self-assembly of DNA nucleobases is essential for biomolecular recognition on surfaces of novel 2D materials. Using atomistic molecular dynamics (MD) simulations, we investigate the self-assembly of guanine and cytosine nucleobases on the hexagonal boron nitride (h-BN) monolayer. We find that the self-assembly is driven by the inherent polarity of the bases determining the nature of molecular ordering and growth patterns: guanine into 2D aggregates and cytosine into 1D linear arrays and interconnected molecular chains. The base–base H-bond interactions guide the self-assembly, and the base-surface interactions facilitate surface recognition and monolayer adsorption. Simulations at elevated temperatures find reconstruction at the surface with cytosine forming distinct 1D chains and guanine forming an extended network. We propose that the distinctive patterns in assembly, unique to the DNA nucleobases, would serve as fingerprints for biomolecular recognition at the solid/li...