Monolayer Boron Research Articles

First-principles study of the electron and phonon transport properties in monolayer boron monosulfide

Abstract Motivated by the excellent electronic properties of theoretical proposed monolayer boron monosulfides (BS) binary materials, which belong to a light-element member of the group IIIA chalcogenides family, we have investigated the electron and phonon transport properties of three monolayer phases of BS (α, β and γ) using first-principles and Boltzmann transport theory methods. The calculated electronic structures show that α- and β-BS are semiconductors with indirect bandgaps of 4.01 eV and 3.87 eV, respectively, whereas the γ-BS is a semiconductor with a direct bandgap of 2.97 eV. Additionally, due to their light carrier effective masses, superior high carrier mobilities are observed, thus bringing high Seebeck coefficients. We also find that due to the absence of imaginary phonon frequencies, the three monolayer phases of BS show dynamical stability. The phonon group velocity and relaxation time are also calculated to analyze the phonon thermal conductivity. We find that strong phonon scattering makes γ-BS monolayer possess extremely low phonon thermal conductivity (1.2 and 2.7 Wm−1K−1 along the x and y directions at 300 K, respectively), whereas α- and β-BS monolayers show a relatively high phonon thermal conductivity. Therefore, the highest predicted ZT value of 1.7 ( n -type) at 700 K is obtained for monolayer γ-BS along the x direction. However, α- and β-BS monolayers have extremely low ZT values. Our results reveal that the γ-BS monolayer has wider promising applications in high performance thermoelectric material than α- and β-BS monolayers.

Band order reversal and valley engineering driving to dual high electron and hole mobility in strained monolayer BS

Strain engineering is an effective method to tune the physical properties of materials. In this work, we found that applying 5% biaxial compression to monolayer boron sulfur can simultaneously induce a band order reversal of valence bands and valley engineering of conduction bands. This change significantly enhances the room temperature intrinsic mobility, boosting it from 2 to 260 cm2 V−1 s−1 for holes and 63 to 543 cm2 V−1 s−1 for electrons. The high hole mobility surpasses that of bulk GaN and silicon. We further demonstrate that the valence band order reversal not only lifts the px/y state above the pz states, giving to a more dispersive highest valence band, and thus smaller electron scattering channels and hole effective mass, but also shifts the stronger σz bonding to weaker π-bonding characteristics, resulting in smaller electron–phonon coupling strength. Those combined effects results in a substantial increase in hole mobility.

First principles study of BN triphenylene-graphdiyne monolayer and bilayer structures with varying C-chain lengths: insights into optical behavior

First-principles calculations engaging density functional theory (DFT) are employed to systematically study the optical characteristics of monolayer and bilayer boron nitride (BN) triphenylene-graphdiyne (Tp-BNyne) structures featuring varying lengths of C-chains. The thermal stability of Tp-BNyne structures at temperatures up to 1000 K is verified. The weak van der Waals interactions due to the small binding energies and significant interlayer distances maintain the cohesion between the layers. The investigation revealed that all Tp-BNyne structures under examination exhibit semiconductor behavior with a band gap in the range of 0.97–2.74 eV. The bilayer configurations demonstrated a narrower energy band gap in comparison to the monolayer ones. Increasing the length of C-chains leads to a reduction in the energy band gap. Delving into the optical behavior of Tp-BNyne structures under photon incidence with parallel and perpendicular polarizations, a distinct anisotropy in the optical characteristics of Tp-BNyne is revealed. The static dielectric constant increases and the optical band gap decreases with increasing C-chain length. The absorption coefficients of monolayer and bilayer Tp-BNyne structures, on the order of 107/m, demonstrate that these sheets can effectively absorb light in the visible and ultraviolet regions. These findings present Tp-BNyne sheets as promising candidates for use in photovoltaic devices to convert sunlight into electrical current, as well as for designing optical devices for ultraviolet protection. Additionally, Tp-BNyne structures are transparent materials, especially in the high-energy range.

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.

Comparison of lattice thermal conductivity using ab-initio DFT, machine learning interatomic potentials, and temperature dependent effective potential: a case study of hexagonal BN and BP bilayer

Discovering high thermal conductivity materials is essential for various practical applications, particularly in electronic cooling. The significance of two-dimensional (2D) materials lies in their unique properties that emerge due to their reduced dimensionality, making them highly promising for a wide range of applications. Hexagonal boron nitride (BN), both monolayer and bilayer forms, has garnered attention for its fascinating properties. In this work, we focus on bilayer boron phosphide (BP), which is isostructural to its BN analogue. The lattice thermal conductivity of both bilayer BN and BP have been calculated using ab-initio density functional theory, machine learning with the moment tensor potential method, and the temperature-dependent effective-potential method (TDEP). The TDEP approach gives more accurate results for both BN and BP materials. The lattice thermal conductivity of bilayer BP is lower than that of bilayer BN at room temperature, attributed to increased phonon anharmonicity. This study highlights the importance of understanding phonon scattering mechanisms in determining the thermal conductivity of 2D materials, contributing to the broader understanding and potential applications of these materials in future technologies.

Bilayer C60 Polymer/h-BN Heterostructures: A DFT Study of Electronic and Optic Properties.

Interest in fullerene-based polymer structures has renewed due to the development of synthesis technologies using thin C60 polymers. Fullerene networks are good semiconductors. In this paper, heterostructure complexes composed of C60 polymer networks on atomically thin dielectric substrates are modeled. Small tensile and compressive deformations make it possible to ensure appropriate placement of monolayer boron nitride with fullerene networks. The choice of a piezoelectric boron nitride substrate was dictated by interest in their applicability in mechanoelectric, photoelectronic, and electro-optical devices with the ability to control their properties. The results we obtained show that C60 polymer/h-BN heterostructures are stable compounds. The van der Waals interaction that arises between them affects their electronic and optical properties.

Advances In Borophene: Synthesis, Tunable Properties, and Energy Storage Applications.

Monolayer boron nanosheet, commonly known as borophene, has garnered significant attention in recent years due to its unique structural, electronic, mechanical, and thermal properties. This review paper provides a comprehensive overview of the advancements in the synthetic strategies, tunable properties, and prospective applications of borophene, specifically focusing on its potential in energy storage devices. The review begins by discussing the various synthesis techniques for borophene, including molecular beam epitaxy (MBE), chemical vapor deposition (CVD), and chemical methods, such as ultrasonic exfoliation and thermal decomposition of boron-containing precursors. The tunable properties of borophene, including its electronic, mechanical, and thermal characteristics, are extensively reviewed, with discussions on its bandgap engineering, plasmonic behavior, and thermal conductivity. Moreover, the potential applications of borophene in energy storage devices, particularly as anode materials in metal-ion batteries and supercapacitors, along with its prospects in other energy storage systems, such as sodium-oxygen batteries, are succinctly, discussed. Hence, this review provides valuable insights into the synthesis, properties, and applications of borophene, offering much-desired guidance for further research and development in this promising area of nanomaterials science.

Structural and mechanical properties of monolayer amorphous carbon and boron nitride

Structural and mechanical properties of monolayer amorphous carbon and boron nitride

Spatially-resolved UV-C emission in epitaxial monolayer boron nitride

We report hyperspectral imaging in the UV-C spectral domain in epitaxial monolayers of hexagonal boron nitride (hBN). Under quasi-resonant laser excitation, the UV-C emission of monolayer hBN consists in resonant Raman scattering and photoluminescence, which appear to be spatially uncorrelated. Systematic measurements as a function of the excitation energy bring evidence of a photoluminescence singlet at ∼6.045 eV. The spatial variations of the photoluminescence energy are found to be around ∼10 meV, revealing that the inhomogeneous broadening is lower than the average photoluminescence linewidth of ∼25 meV, a value close to the radiative limit in monolayer hBN. Our methodology provides an accurate framework for assessing the opto-electronic properties of hBN in the prospect of scalable hBN-based devices fabricated by epitaxy.

Structural, electronic and thermoelectric properties of boron phosphorous nitride B2PN via first principles study.

A theoretical study of monolayer boron phosphorous nitride (B2PN) is performed to explore its electronic and thermoelectric properties. The thermodynamic stability is determined by the formation energy of a monolayer. The dynamic stability is obtained from the phonon dispersion curve. We performed an AMID simulation to ensure the thermal stability and found that our material is thermally stable at 700 K. The system possesses direct band gaps of 0.25 eV and 0.4 eV with Perdew-Burke-Ernzerhof (PBE) and hybrid functional (HSE), respectively. The Seebeck coefficient is found to be the same in both directions, and the maximum value is 1.55 mV K-1. The relaxation time is found to be longer for the hole-doped system than the electron-doped system. It is observed that electrical conductivity is greater for hole-doped system in both directions, and a similar trend is observed for electronic thermal conductivity. We found that the lattice thermal conductivity of our systems is anisotropic. The lattice thermal conductivity along the Y-direction is greater than that in the X-direction. The calculation performed for the figure of merit (ZT) reveals that the system has a high ZT of 1.14 for a hole-doped system. The figure of merit makes the system a promising candidate for potential thermoelectric device applications.

Non-identical moiré twins in bilayer graphene

The superlattice obtained by aligning a monolayer graphene and boron nitride (BN) inherits from the hexagonal lattice a sixty degrees periodicity with the layer alignment. It implies that, in principle, the properties of the heterostructure must be identical for 0° and 60° of layer alignment. Here, we demonstrate, using dynamically rotatable van der Waals heterostructures, that the moiré superlattice formed in a bilayer graphene/BN has different electronic properties at 0° and 60° of alignment. Although the existence of these non-identical moiré twins is explained by different relaxation of the atomic structures for each alignment, the origin of the observed valley Hall effect remains to be explained. A simple Berry curvature argument is not sufficient to explain the 120° periodicity of this observation. Our results highlight the complexity of the interplay between mechanical and electronic properties in moiré structures and the importance of taking into account atomic structure relaxation to understand their electronic properties.

Unidirectional Nano-modulated Binding and Electron Scattering in Epitaxial Borophene.

A complex interplay between the crystal structure and the electron behavior within borophene renders this material an intriguing 2D system, with many of its electronic properties still undiscovered. Experimental insight into those properties is additionally hampered by the limited capabilities of the established synthesis methods, which, in turn, inhibits the realization of potential borophene applications. In this multimethod study, photoemission spectroscopies and scanning probe techniques complemented by theoretical calculations have been used to investigate the electronic characteristics of a high-coverage, single-layer borophene on the Ir(111) substrate. Our results show that the binding of borophene to Ir(111) exhibits pronounced one-dimensional modulation and transforms borophene into a nanograting. The scattering of photoelectrons from this structural grating gives rise to the replication of the electronic bands. In addition, the binding modulation is reflected in the chemical reactivity of borophene and gives rise to its inhomogeneous aging effect. Such aging is easily reset by dissolving boron atoms in iridium at high temperature, followed by their reassembly into a fresh atomically thin borophene mesh. Besides proving electron-grating capabilities of the boron monolayer, our data provide comprehensive insight into the electronic properties of epitaxial borophene which is vital for further examination of other boron systems of reduced dimensionality.

Electrochemical CO2 reduction on metal-silicon centered single-atom dual site catalyst: A computational study

In this work, we employed density functional theory (DFT) computations to design innovative electrocatalysts for the electrochemical CO2 reduction reaction (ECRR). Specifically, we focused on single-metal dual site catalysts (SM-DSCs) based on monolayer boron nitride (BN) modified with silicon (Si) or carbon (C) coordinating atoms. These materials, denoted as M@BN_D(V) (BN = boron nitride monolayer; D = Si or C atom; M = metal atoms; V = B vacancy or N vacancy), were investigated as the potential electrocatalysts for the ECRR. Our computational results revealed that Fe@BN_Si(B) and Fe@BN_C(N) were the most stable forms for Fe@BN_Si(V) and Fe@BN_C(V), respectively. After that, we proceeded to analyze CO2 adsorption as well as reduction pathways for the ECRR based on the calculated Gibbs energy and the competitive hydrogen evolution reaction (HER). Among the Fe-based catalysts, Fe@BN_Si(B) exhibited a lower limiting potential (UL) of –0.63 V, while Fe@BN_C(N) required a higher UL of –0.72 V for the production of CH4(g). Notably, both Fe@BN_Si(B) and Fe@BN_C(N) catalysts displayed high selectivity compared to the HER. Accordingly, Fe@BN_Si(B) and Fe@BN_C(N) catalysts are emerged as the promising electrocatalyst candidates for the ECRR. In addition, the UL required to overcome was reduced to –0.35 V for WFe@BN_Si(B) in a water co-adsorption environment, suggesting the catalytic performance can be enhanced by water promotion effect.

Effect of low nitrogen concentration on reactive RF sputtering of boron

Monolayer boron and B/Mo/B/Mo coatings were prepared by reactive magnetron sputtering in the N2/Ar atmosphere with different RF powers, and the effect of the N2:Ar flow ratio was studied. It was found that as the N2:Ar flow ratio increased, the deposition rate of boron coatings exhibited three different stages of variation due to different mechanisms. The variation of deposition rate with increasing N2:Ar flow ratio was consistent for different RF powers. Berg's model explained experimental findings. XPS revealed that the coatings contained more than 86 % boron nitride (BN) when the N2 flow ratio was above 0.053 at 300W RF power. An optimal ratio exists that maximizes the boron deposition rate and produces a nearly pure boron nitride coating without target poisoning.

Electro-optical properties of strained monolayer boron phosphide

In this paper, we use tight-binding approximation and linear response theory to study the electronic and optical properties of strained monolayer boron-phosphide (h-BP). Compared with the previous DFT study and adding on-site energy variation to the Hamiltonian, we propose a theoretical approach to investigate the strain effects on the electronic and optical properties of the h-BP. Applying tensile strain increases the gap while compressive strain reduces it as the maximum and minimum of the gap are 1.45 eV and 1.14 eV respectively and are related to the biaxial strain. Also, we investigate the optical conductivity and electron energy loss spectrum (EELS) of the pristine and strained h-BP. The absorption peak of the Resigma_{xx,yy} appears in energy about 4 eV but applying strain shifts the peak’s energy. Optical properties of pristine h-BP are isotopic and biaxial strain preserves this isotropy, but uniaxial strain exerts anisotropic behavior in the system.

Ballistic transport in 5.1 nm monolayer boron phosphide transistors for high-performance applications

Boron Phosphide is reported to be a semiconductor material with anisotropy, tunable bandgap, and high carrier mobility. We study the performance of 5.1 nm metal–oxide–semiconductor field-effect transistors (MOSFETs) based on boron phosphide using quantum transport simulation. The calculated results show that the on-state current can fulfill the requirements of the International Semiconductor Technology Roadmap (ITRS) for high-performance (HP) devices at the optimal doping concentration, but the gate control capability is not ideal. Furthermore, it is found that the gate control capability and on-state current can be significantly improved with the length being 1 nm by using the underlap (UL) structure. We also study the performance of boron phosphide MOSFET with different gate lengths (5–8 nm), and the results suggest that the shorter the gate length, the worse the gate control capability. Interestingly, the p-type boron phosphide MOSFET always outperforms the n-type MOSFET. This work will provide a new reference for the development of two-dimensional (2D) semiconductor devices.

Interaction between bilayer borophene and metal or inert substrates

Bilayer borophene have gradually come into our horizons in experimental and theoretical studies due to the superior antioxidation and advantageous to the exfoliation compared with monolayer borophene. Using systematical first-principles calculations, we explore the interactions between bilayer borophene and various metal surfaces of Ag (111), Au (111), Al (111), Cu (111) and inert substrates of monolayer hexagonal boron nitride (h-BN), monolayer MoS2 and GaN (0001) surface. The electronic band structures, partial density of states, total electron distribution and Bader charge analysis have been systematically calculated to explore for the interaction strength. The orbital hybridization and chemical bonding occur in the interface of four metals and GaN heterostructures attributed to the active surficial atoms, differ from Van Der Waals interaction of borophene-MoS2 and h-BN inert substrates. In addition, we find that metal Al (111) with smaller work function and inert substrates of monolayer h-BN and MoS2 have tiny tunneling barrier at the interface of bilayer borophene-substrates, and might be appropriate to the synthesis of bilayer borophene.

Two-dimensional BAs/GeC van der waals heterostructures: A widely tunable photocatalyst for water splitting and hydrogen production

Of late, two-dimensional van der Waals heterostructures (vdWHs) have gained tremendous attention for water-splitting to produce hydrogen (H2) fuel. This work demonstrates various configurations of vdWHs made up of monolayer boron arsenide (BAs) and germanium carbide (GeC) that exhibit outstanding photocatalytic properties in the water-splitting process to generate H2 fuel. The absorption coefficient of the proposed BAs/GeC vdWHs is more than 105 cm−1, which exceeds the extensive conversion efficiency of optoelectronic materials. The absorption coefficient can be further tuned and reaches a maximum value of 2.6×105 cm−1 when applying an external strain. Dynamically tunable bandgaps in the range of 0.78–2.02 eV are found in these vdWHs by applying a biaxial strain. A strong photocatalytic water splitting action throughout the ultraviolet to optical spectrum region is found when a biaxial strain of −6% to +6% is applied. The favorable characteristics of the proposed BAs/GeC vdWHs could help enhance H2 fuel generation via water splitting.

Developing a novel radial ultrasonic vibration-assisted grinding device and evaluating its performance in machining PTMCs

Particle-reinforcing titanium matrix composites (PTMCs) exhibit the sharp raising applications in modern industries owing to its extraordinary physical and mechanical properties. However, the poor grindability and unstable grinding processes due to the existence of TiC particles and TiB short fibres inside PTMCs, leading to the sudden grinding burn and low material removal rate. In this work, a novel radial ultrasonic vibration-assisted grinding (RUVAG) device with a special cross structure was developed to improve machining efficiency and avoid grinding burns. Meanwhile, the resonant modal and transient dynamic characteristics of radial ultrasonic vibration system were discussed. Comparative grinding performance experiments were then conducted under the conventional grinding (CG) and RUVAG using mono-layer cubic boron nitride abrasive wheels, in views of the grinding forces and force ratio, grinding temperature, and ground surface morphology. Results show that the ultrasonic vibration direction can be transformed effectively using the special cross structure of vibration converter, and better vibration homogeneity can be obtained. RUVAG has a smaller tangential grinding force by 5.0%–17.2% than that of CG, but a higher normal grinding force of 6.5%–14.9%, owing to the periodic impact of grinding wheels. In addition, RUVAG possesses a remarkable lower grinding temperature in range of 24.2%–51.8% and a higher material removal rate by 2.8 times compared with CG, resulting from the intermittent cutting behavior between the grinding wheel and workpiece. In this case, the sudden burn can be avoided during high-speed grinding processes. Moreover, the proportion of micro-fracture defects on machined surface is slightly increased once the ultrasonic vibration mode is employed because of the periodic impact on reinforced particles, whereas the pull-out defects of reinforced particles are reduced significantly.

Prediction of a planar BxP monolayer with inherent metallicity and its potential as an anode material for Na and K-ion batteries: a first-principles study.

Borophene, the lightest two-dimensional material, exhibits exceptional storage capacity as an anode material for sodium-ion batteries (NIBs) and potassium-ion batteries (PIBs). However, the pronounced surface activity gives rise to strong interfacial bonding between borophene and the metal substrate it grows on. Incorporation of heterogeneous atoms capable of forming strong bonds with boron to increase borophene stability while preserving its intrinsic metallic conductivity and high theoretical capacity remains a great challenge. In this study, a particle swarm optimization (PSO) method was employed to determine several new two-dimensional monolayer boron phosphides (BxP, x = 3-6) with rich boron components. The obtained BxP has great potential to be used as an anode material for sodium-ion batteries/potassium-ion batteries (SIBs/PIBs), according to DFT calculations. BxP demonstrates remarkable stability compared with borophene which ensures their feasibility of experimental synthesis. Moreover, B5P and B6P exhibit high electronic conductivity and ionic conductivity, with migration energy barriers of 0.20 and 0.21 eV for Na ions and 0.07 eV for K ions. Moreover, the average open circuit voltage falls within a favorable range of 0.25-0.73 V, which results in a high storage capacity of 1119-2103 mA h g-1 for SIBs and 631-839 mA h g-1 for PIBs. This study paves the way for exploring boron-rich 2D electrode materials for energy applications and provides valuable insights into the functionalization and stabilization of borophene.