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In this work, mild steel as a substrate was coated by electrodeposition in a bath mixed with nickel sulfate (NiSO4·6H2O), nickel chloride (NiCl4·6H2O), and boric acid (H3BO3) using nanocomposite cetyltrimethylammonium bromide, hBN, and epoxy with hardener. The experiments were designed using the Taguchi method through the L9 orthogonal array to reduce the number of experiments. The input parameters for the design of experiments were taken: the time (min), voltage (V), and the hBN concentration (wt-%). The coated samples were tested for their tribological, corrosion, and adhesion performance using pin-on-disc, electro-impedance spectroscopy, and cross hatch tester, respectively. The tribological results reveal that the coated sample of 3 wt-% hBN concentration at 3 mV voltage and 30-minute deposition time shows the lowest friction coefficient (∼0.42) among all the samples, indicating its superior wear resistance and corrosion resistance. Further, the same sample also outperformed the others, demonstrating the high adhesion (adhesion scale of 5 B) of coating with the substrate. Moreover, the surface was characterized using X-ray diffraction, Fourier transforms infrared, goniometer, and scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Integrating quantum materials with fiber optics adds advanced functionalities to a variety of applications, and introduces fiber‐based quantum devices such as remote sensors capable of probing multiple physical parameters. However, achieving optimal integration between quantum materials and fibers is challenging, particularly due to difficulties in fabrication of quantum elements with suitable dimensions and an efficient photonic interface to a commercial optical fiber. Here a new modality for a fiber‐integrated van der Waals quantum sensor is demonstrated. A hole‐based circular Bragg grating cavity from hexagonal boron nitride (hBN) is designed and fabricated, engineer optically active spin defects within the cavity, and integrate the cavity with an optical fiber using a deterministic pattern transfer technique. The fiber‐integrated hBN cavity enables efficient excitation and collection of optical signals from spin defects in hBN, thereby enabling all‐fiber integrated quantum sensors. Moreover, remote sensing of a ferromagnetic material and of arbitrary magnetic fields is demonstrated. All in all, the hybrid fiber‐based quantum sensing platform may pave the way to a new generation of robust, remote, multi‐functional quantum sensors. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride (hBN) holds promise as a solid state, van der Waals host of single photon emitters for on‐chip quantum photonics. The B‐center defect emitting at 436 nm is particularly compelling as it can be generated by electron beam irradiation. However, the emitter generation mechanism is unknown, the robustness of the method is variable, and it has only been applied successfully to thick flakes of hBN (≫ 10 nm). Here, it is used in situ time‐resolved cathodoluminescence (CL) spectroscopy to investigate the kinetics of B‐center generation. It is shown that the generation of B‐centers is accompanied by quenching of a carbon‐related emission at ≈305 nm and that both processes are rate‐limited by electromigration of defects in the hBN lattice. It identifies problems that limit the efficacy and reproducibility of the emitter generation method and solve them using a combination of optimized electron beam parameters and hBN pre‐and postprocessing treatments. It is achieved B‐center quantum emitters in hBN flakes as thin as 8 nm, elucidate the mechanisms responsible for electron beam restructuring of quantum emitters in hBN, and gain insights toward the identification of the atomic structure of the B‐center quantum emitter. [ABSTRACT FROM AUTHOR]

Ensuring high‐quality surface passivation is the key to realizing high‐performance self‐powered optoelectronic devices, as it significantly impacts carrier transport. 2D hexagonal boron nitride (hBN) exhibits exceptional material characteristics, including a wide bandgap, high dielectric constant, minimized dangling bonds, and high chemical stability, making it one of the most promising candidates for high‐quality passivation. Nevertheless, the passivation characteristics of hBN on Ge and their influence on self‐powered photodetection remain unexplored, as well as their effects on carrier recombination lifetime, interface defect density, and Schottky barrier height. In this study, the first demonstration of enhanced Schottky junction photodiode characteristics and the impact of the surface passivation on carrier lifetime and defect density using an hBN monolayer on Ge are presented. The characteristics of hBN/Ge with Al2O3/Ge are compared to demonstrate the superior passivation quality of hBN over conventional materials. These results highlight the significant potential of hBN as an effective passivation for optoelectronic device applications. [ABSTRACT FROM AUTHOR]

Converting transverse photons into longitudinal two-dimensional plasmon-–polaritons (2D-PP) and vice versa presents a significant challenge within the fields of photonics and plasmonics. Therefore, understanding the mechanism which increases the photon – 2D-PP conversion efficiency could significantly contribute to those efforts. In this study, we theoretically examine how efficiently incident radiation, when scattered by a silver spherical nanoparticle (Ag-NP), can be transformed into 2D-PP within van der Waals (vdW) heterostructures composed of hexagonal boron nitride and graphene (hBN/Gr composites). We show that the Dirac plasmon (DP) excitation efficiency depends on the Ag-NP radius as R3, and decreases exponentially with Ag-NP height h, so that for a certain Ag-NP geometry up to 25 % of the incident electrical field is channeled into the DP. We demonstrate that the linear plasmons (LPs) excitation efficiency can be manipulated by changing the graphene–graphene distance Δ (or hBN thickness) or by changing the number of graphene layers N. By increasing Δ and/or N the LPs move towards smaller wave vectors Q and become accessible by the Ag-NP dipole field, so that for N ≥ 5 the excitation of more than one LP is possible. These results are supported by recent scattering-type scanning near-field optical microscopy (s-SNOM) measurements. Furthermore, we show that Ag-NPs with specific parameters preferentially hybridizes with DPs of a particular wavelength λD, facilitating selective excitation of DPs. The obtained tuning possibilities could have a significant impact on applied plasmonics, photonics or optoelectronics. [ABSTRACT FROM AUTHOR]

In this work, a self-lubricating composite was manufactured using a novel hybrid 3D printing/in situ spraying process that involved the printing of an acrylonitrile butadiene styrene (ABS) matrix using fused deposition modeling (FDM), along with the in situ spraying of alumina (Al2O3) and hexagonal boron nitride (hBN) reinforcements during 3D printing. The results revealed that the addition of the reinforcement induced an extensive formation of micropores throughout the ABS structure. Under tensile-loading conditions, the mechanical strength and cohesive interlayer bonding of the composites were diminished due to the presence of these micropores. However, under tribological conditions, the presence of the Al2O3 and hBN reinforcement improved the frictional resistance of ABS in extreme loading conditions. This improvement in frictional resistance was attributed to the ability of the Al2O3 reinforcement to support the external tribo-load and the shearing-like ability of hBN reinforcement during sliding. Collectively, this work provides novel insights into the possibility of designing tribologically robust ABS components through the addition of in situ-sprayed ceramic and solid-lubricant reinforcements. [ABSTRACT FROM AUTHOR]

Large-scale synthesis of hexagonal boron nitride (hBN) by a liquid exfoliation technique has been demonstrated in the present study. It is a low-cost and efficient method for exfoliating 2D materials like hBN. Here, a two-step approach was acquired to exfoliate the bulk hBN. In the first step, the bulk hBN was dispersed using a probe sonicator in a solution of gelatin, potassium chloride (KCl) and zinc chloride (ZnCl2), and in the second step, further exfoliation was achieved by centrifugation process. Exfoliation was achieved by both centrifugation and intercalation of Zn2+ and K+ ions within the layers of hBN. The supernatant obtained after centrifugation was heated to 600 °C for a duration of 1 h in an air atmosphere to eliminate the gelatin which was again heat treated for the same duration at 800 °C in an Ar atmosphere to improve its crystallinity. The hBN nanoplatelets obtained from the bulk hBN were characterized using various analytical techniques such as x-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), differential scanning calorimetry and thermogravimetric analysis (DSC/TGA) and atomic force microscopy (AFM) to determine their properties. The hBN nanoplatelets showed a thickness range of ~ 50-270 nm and a lateral dimension range of ~ 1-3 μm. FTIR analysis confirmed the presence of hydroxyl (OH) functional group attached to the hBN nanoplatelets due to the absorption of surface moisture. The hBN nanoplatelets showed excellent thermal stability up to a temperature of ~ 726.16 °C. The liquid exfoliation approach used in the present work was found to be a highly effective method and shows potential for producing hBN nanoplatelets with a few layers. [ABSTRACT FROM AUTHOR]

Titanium alloy is an essential material for preparing aerospace engines because of its excellent performance. However, the poor wear resistance of titanium alloy restricts its further development as a critical engine material. This study aimed to use laser cladding and particle enhancement technologies to enhance the surface wear resistance of titanium alloy. (NiCoCr) 94 Al 3 Ti 3 +hBN, (NiCoCr) 94 Al 3 Ti 3 +cBN, and (NiCoCr) 94 Al 3 Ti 3 +hBN + cBN were prepared on the surface of titanium alloy, and the wear resistance mechanism of single-phase self-lubricating particles, single-phase hard particles, and self-lubricating and hard biphasic particles was investigated. The results showed that the microhardness of the biphase-reinforced coating was 1083.8 HV0.5, which was higher than that of the self-lubricating particle-reinforced coating and hard-particle-reinforced coating by 368.4 HV0.5 and 149.8 HV0.5, respectively. The friction coefficient of the biphase-reinforced coating was 0.4208, which was lower than that of the self-lubricating particle-reinforced coating and hard-particle-reinforced coating by 0.0224 and 0.0686, respectively. The wear rate of the biphase-reinforced coating was 0.076 mm3/NM, and the wear resistance of the biphase-reinforced coating was 3.42 and 1.37 times that of the self-lubricating particle-reinforced coating and hard-particle-reinforced coating, respectively. hBN relied on its own decomposition to promote the coating to present a layered unstable structure to achieve a wear reduction effect, cBN relied on its own hardness to resist wear and played a wear-resistant role, whereas biphase-reinforced coating had a hard wear resistance and formed a lubricating film to enhance the wear resistance of the coating. The comprehensive performance of the dual-phase wear-resistant coating reinforced by hard particles and self-lubricating particles was better than that of single-phase wear-resistant coating, providing a reference for developing wear-resistant coating integrating hardness and self-lubrication. [ABSTRACT FROM AUTHOR]

Single-photon sources are important for integrated photonics and quantum technologies, and can be used in quantum key distribution, quantum computing, and sensing. Color centers in the solid state are a promising candidate for the development of the next generation of single-photon sources integrated in quantum photonics devices. They are point defects in a crystal lattice that absorb and emit light at given wavelengths and can emit single photons with high efficiency. The landscape of color centers has changed abruptly in recent years, with the identification of a wider set of color centers and the emergence of new solid-state platforms for room-temperature single-photon generation. This review discusses the emerging material platforms hosting single-photon-emitting color centers, with an emphasis on their potential for the development of integrated optical circuits for quantum photonics. [ABSTRACT FROM AUTHOR]

While hexagonal boron nitride (hBN) has been widely used as a buffer or encapsulation layer for emerging electronic devices, interest in utilizing it for large‐area chemical barrier coating has somewhat faded. A chemical vapor deposition process is reported here for the conformal growth of hBN on large surfaces of various alloys and steels, regardless of their complex shapes. In contrast to the previously reported very limited protection by hBN against corrosion and oxidation, protection of steels against 10% HCl and oxidation resistance at 850 °C in air is demonstrated. Furthermore, an order of magnitude reduction in the friction coefficient of the hBN coated steels is shown. The growth mechanism is revealed in experiments on thin metal films, where the tunable growth of single‐crystal hBN with a selected number of layers is demonstrated. The key distinction of the process is the use of N2 gas, which gets activated exclusively on the catalyst's surface and eliminates adverse gas‐phase reactions. This rate‐limiting step allowed independent control of activated nitrogen along with boron coming from a solid source (like elemental boron). Using abundant and benign precursors, this approach can be readily adopted for large‐scale hBN synthesis in applications where cost, production volume, and process safety are essential. [ABSTRACT FROM AUTHOR]

Electrochemical discharge machining (ECDM) is an emerging micromachining method to drill advanced non-conductive materials such as Hexagonal boron nitride (hBN). Physical contact of micro tools with work material could cause machining inaccuracies, excessive tool wear, and even tool breakage. In this study, a control system based on monitoring the force generated by the ECDM gas film has been developed to achieve non-contact machining of ECDM by dynamically adjusting the tool feed rate. The accuracy of the control system was verified by accelerometer and Fast Fourier Transformation (FFT) data. In the modules, it was found that a non-contact machining process requires the FFT amplitude to be lower than 42 V for a 1200 rpm tool rotation. The experimental results show consistent micro-holes with an average diameter of 650 µm and less than 20 µm error in the overcut achieved using this control system. [ABSTRACT FROM AUTHOR]

The present investigation demonstrates the feasibility of obtaining a wide range in friction and wear for SiC-hBN composites in sliding conditions: humidity (≤ 20 % RH and ≥ 90 % RH) and temperature (RT and 500 °C) against SiC ball. With an increase in hBN content to 10 vol%, wear rate reduced by an order of magnitude irrespective of humidity at RT and up to 55 % reduction at 500 °C, and coefficient of friction (COF) reduced by 76 % at high-humidity. Friction and wear results corroborate with the transition in material removal mechanism from fracture of SiC grains and pull-out of hBN platelets at ≤ 20 % RH to hydroxylative wear at ≥ 90 % RH and oxidative wear at 500 °C. SiC-10 vol% hBN composites are recommended for wear-resistance applications experiencing extreme conditions of humidity and temperature as well as applications where internal lubrication is the only feasible method for reducing friction. [Display omitted] [ABSTRACT FROM AUTHOR]

Visualization of layered materials with atomic-scale thickness by optical interference with a low-reflection substrate has been widely used to identify exfoliated thin flakes. However, the identification of optically transparent films with an atomic-scale thickness, such as hexagonal boron nitride (hBN), requires a substrate with a reflectance lower than a few percent. Although several types of multilayer antireflection (AR) substrates for identification have been developed, the lack of an established optical design limits the layer structure of AR coatings. In this study, the reflection circle diagram-based design of the AR coatings with a layer of arbitrary materials on top is proposed. The AR substrates with diverse materials on top would visualize the various organic monolayers formed on substrates with chemical bonding. As an experimental demonstration, Si substrates with an optically designed double-layer AR coating of SiNx and SiO2 were assessed by reflection spectroscopy and employed to visualize an exfoliated monolayer hBN film. As a result, the presence of the monolayer films on Si/SiNx (50 nm)/SiO2 (25 nm) was directly identified in the image photographed by a commercial camera without an optional optical filter and image processing. Additionally, the use of a narrow band-pass filter enhanced the optical contrast of the monolayer hBN up to 17% at 470 nm and enabled easy determination of the number of layers in few-layer hBN flakes. [ABSTRACT FROM AUTHOR]

Boron vacancies (VB–) in hexagonal boron -nitride (hBN) have sparked great interest in recent years due to their optical and spin properties. Since hBN can be readily integrated into devices where it interfaces a huge variety of other 2D materials, boron vacancies may serve as a precise sensor which can be deployed at very close proximity to many important materials systems. Boron vacancy defects may be produced by a number of existing methods, the use of which may depend on the final application. Any method should reproducibly generate defects with controlled density and desired pattern. To date, however, detailed studies of such methods are missing. In this paper, we study various techniques for the preparation of hBN flakes from bulk crystals and relevant postprocessing treatments, namely, focused ion beam (FIB) implantation, for creation of VB–s as a function of flake thickness and defect concentrations. We find that flake thickness plays an important role when optimizing implantation parameters, while careful sample cleaning proved important to achieve consistent results. [ABSTRACT FROM AUTHOR]

This paper aims to study the reflection characteristics of optical beams in a hybrid graphene–hexagonal boron nitride (hBN)–graphene structure, which has been located on SiO2-Si layers. An analytical model is presented to derive the reflection characteristics by using the transfer matrix method. The upper Reststrahlen band has been chosen as the studied frequency range. It is shown that the characteristics of the reflected beam can be effectively controlled by varying the chemical potential of graphene sheets. The obtained results represent a high value of the reflected group delay ( τ r = 15.3 p s ) at the frequency of 24.9 THz. The presented investigation will be helpful to control the group delays of reflected beams and can be utilized for the design of innovative graphene–hBN devices in the mid-infrared wavelengths. [ABSTRACT FROM AUTHOR]

Abstract Valley Hall effect is observed in asymmetric single‐layer and bilayer graphene systems. In single‐layer graphene systems, asymmetry is introduced by aligning graphene with hexagonal boron nitride (hBN) with a near‐zero twist angle, breaking the sub‐lattice symmetry. Although a similar approach is used in bilayer graphene to break the layer symmetry and thereby observe the valley Hall effect, the bilayer graphene is sandwiched with hBN on both sides in those studies. This study looks at a much simpler, non‐encapsulated structure where hBN is present only at the top of graphene. The crystallographic axes of both hBN and bilayer graphene are aligned. A clear signature of the valley Hall effect through non‐local resistance measurement (RNL) is observed. The observed non‐local resistance can be manipulated by applying a displacement field across the heterostructure. Furthermore, the electronic band structure and Berry curvature calculations validate the experimental observations.

Abstract While hexagonal boron nitride (hBN) has been widely used as a buffer or encapsulation layer for emerging electronic devices, interest in utilizing it for large‐area chemical barrier coating has somewhat faded. A chemical vapor deposition process is reported here for the conformal growth of hBN on large surfaces of various alloys and steels, regardless of their complex shapes. In contrast to the previously reported very limited protection by hBN against corrosion and oxidation, protection of steels against 10% HCl and oxidation resistance at 850 °C in air is demonstrated. Furthermore, an order of magnitude reduction in the friction coefficient of the hBN coated steels is shown. The growth mechanism is revealed in experiments on thin metal films, where the tunable growth of single‐crystal hBN with a selected number of layers is demonstrated. The key distinction of the process is the use of N2 gas, which gets activated exclusively on the catalyst's surface and eliminates adverse gas‐phase reactions. This rate‐limiting step allowed independent control of activated nitrogen along with boron coming from a solid source (like elemental boron). Using abundant and benign precursors, this approach can be readily adopted for large‐scale hBN synthesis in applications where cost, production volume, and process safety are essential.

Hexagonal boron nitride (hBN) with excellent self-lubrication performance is expected to relieve the friction resistance and wear of NiCr–Cr 3 C 2 coatings. However, the poor wettability of hBN with most materials makes it difficult to fabricate NiCr–Cr 3 C 2 -hBN composite coating with good cohesion strength. In this study, hBN was firstly pretreated through magnetron-sputtering aided Ni plating to form hBN@Ni particles. Then, NiCr–Cr 3 C 2 -hBN@Ni powder was prepared by spray granulation. Next, corresponding coatings were prepared through supersonic atmosphere plasma spraying. It was found that in comparison with NiCr–Cr 3 C 2 -hBN coating, the NiCr–Cr 3 C 2 -hBN@Ni coating exhibited a decreased porosity (from 3.6% to 0.3%), elevated cohesion (from 52.78 N to 62.11 N), and the wear rate decreased by an order of magnitude. It was concluded that hBN@Ni can effectively improve the component interface inside powder, enhance the cohesion of molten in-flight particles, and make the internal structure of the coating denser. [ABSTRACT FROM AUTHOR]

In this work, a self-lubricating composite was manufactured using a novel hybrid 3D printing/in situ spraying process that involved the printing of an acrylonitrile butadiene styrene (ABS) matrix using fused deposition modeling (FDM), along with the in situ spraying of alumina (Al2O3) and hexagonal boron nitride (hBN) reinforcements during 3D printing. The results revealed that the addition of the reinforcement induced an extensive formation of micropores throughout the ABS structure. Under tensile-loading conditions, the mechanical strength and cohesive interlayer bonding of the composites were diminished due to the presence of these micropores. However, under tribological conditions, the presence of the Al2O3 and hBN reinforcement improved the frictional resistance of ABS in extreme loading conditions. This improvement in frictional resistance was attributed to the ability of the Al2O3 reinforcement to support the external tribo-load and the shearing-like ability of hBN reinforcement during sliding. Collectively, this work provides novel insights into the possibility of designing tribologically robust ABS components through the addition of in situ-sprayed ceramic and solid-lubricant reinforcements.

Emergent heat transfer and thermal management applications require polymer composites with enhanced thermal conductivity (κ). Composites filled with non-spherical fillers, such as hexagonal boron nitride (hBN) and Graphite (Gr), suffer from processing-induced filler orientations, resulting in anisotropic κ, commonly low in the through-plane direction. Here, the effects of extrusion and compression molding-induced orientations on κ of hBN- and Gr-filled polyethylene composites were investigated. The effect of extrusion on the hBN orientation was studied using dies of various shapes. The shaped extrudates exhibited hBN orientations parallel to the extrusion flow direction, which prompted additional hBN orientation during compression molding. κ of the composites produced with shaped extrudates varied from 0.95 to 1.67 W m−1 K−1. Pelletizing and crushing the extrudates improved κ, by exploiting and eliminating the effect of extrusion-induced hBN orientations. Gr-filled composites showed better κ than hBN composites due to the higher intrinsic conductivity and bigger particle sizes. A maximum κ of 5.1 and 11.8 W m−1 K−1 was achieved in composites with oriented hBN and Gr through a thin rectangular die and stacking the sheets to fabricate composites with highly oriented fillers. [ABSTRACT FROM AUTHOR]

The aim of this research was to analyze the effect of inorganic additives on the tribological properties of the high-density polyethylene (HDPE) matrix composite surface. Titanium (Ti) and hexagonal boron nitride (hBN) were added in different mass fractions. The samples were produced by pressing a pre-prepared mixture of granules. The composite samples with the following mass fractions of additives were fabricated: 5% hBN, 10% hBN, 28% Ti–2% hBN, 23% Ti–7% hBN, and 20% Ti–10% hBN. An even distribution of individual additives' concentrations was confirmed. Observations of morphology, surface topography, hardness, and tribological measurements were conducted using reciprocating motion tests with the "pin-on-flat" and rotational tests with the "pin-on-disc" configuration. Subsequently, microscopic observations and measurements of the wear track profile were carried out. Additionally, geometry parameters of the contacting elastic body were calculated for various counter-samples. It was found that the Shore D hardness of samples containing Ti and hBN increased with the Ti content, while the coefficient of friction (COF) value decreased. The addition of hBN alone did not significantly affect the hardness, regardless of the ratio, while the COF increased with the increasing hBN content. The COF value doubled with the addition of 10% hBN (COF = 0.22), whereas the addition of 90% Ti–10% hBN resulted in a decrease in the COF value, to COF = 0.83. The highest hardness value was obtained for the sample containing 28% Ti–2% hBN (66.5), while the lowest was for the sample containing 10% hBN (63.2). The wear track analysis, including its height and width caused by deformation, was detected using a focal differentiation microscope and scanning electron microscopy. Additionally, EDS maps were generated to determine the wear characteristics of the composite. [ABSTRACT FROM AUTHOR]

Reactive sintering has been widely utilized to densify ceramics. Although the technology has numerous advantages, the composition of as-sintered ceramics is hard to be adjusted unless additional products are added. In this work, a novel solid-state route based on the reactions among TiN, Al and B were proposed to consolidate TiB 2 -AlN- h BN ceramics (TAB) with tunable compositions (h BN ≤ 42 vol%, AlN ≤ 45 vol%). Dense TAB with high relative density, refined grain size and homogeneous microstructure were obtained via spark plasma sintering at 1800 °C and 60 MPa. It was found that exothermic reactions between the reactants could be ignited during heating, and the order of temperature at which the combustion process occurred was just opposite to the sequence of adiabatic temperature for individual reactions. Effects of h BN and AlN amounts on the densification, microstructure, mechanical properties, machinability and electrical resistivity of as-sintered ceramics were comprehensively investigated. Compared to AlN, h BN content played a more obvious role on those properties. As h BN contents increased from 0 to 42 vol%, the flexural strength, fracture toughness, Vickers hardness and modulus of TAB continuously decreased. TAB with h BN amounts ≥ 13 vol% exhibited better machinability with surface roughness lower than 2.9 µm after machining. Nevertheless, their electrical resistivity values at room temperature fluctuated in a narrow range between 43 μΩ·cm and 83 μΩ·cm, irrelevant with the h BN amounts. • TiB 2 -AlN- h BN ceramics with tunable compositions were reactively densified without adding external h BN or AlN at reduced temperature. • Relationships between the adiabatic temperature and the temperature when reactions occurred in the TiN-Al-B system were investigated. • TiB 2 -AlN- h BN ceramics with synergistically improved mechanical, electrical and machinability were achieved. [ABSTRACT FROM AUTHOR]

Membranes that selectively filter for both anions and cations are central to technological applications from clean energy generation to desalination devices. 2D materials have immense potential as these ion-selective membranes due to their thinness, mechanical strength, and tunable surface chemistry; however, currently, only cation-selective membranes have been reported. Here we demonstrate the controllable cation and anion selectivity of both monolayer graphene and hexagonal boron nitride. In particular, we measure the ionic current through membranes grown by chemical vapor deposition containing well-known defects inherent to scalably produced and wet-transferred 2D materials. We observe a striking change from cation selectivity with monovalent ions to anion selectivity by controlling the concentration of multivalent ions and inducing charge inversion on the 2D membrane. Furthermore, we find good agreement between our experimental data and theoretical predictions from the Goldman-Hodgkin-Katz equation and use this model to extract selectivity ratios. These tunable selective membranes conduct up to 500 anions for each cation and thus show potential for osmotic power generation.

Phonon-polaritons (PhPs) in layered crystals, including hexagonal boron nitride (hBN), have been investigated by combined scattering-type scanning near-field optical microscopy (s-SNOM) and Fourier transform infrared (FTIR) spectroscopy. Nevertheless, many of such s-SNOM-based FTIR spectra features remain unexplored, especially those originated from the impact of boundaries. Here we observe real-space PhP propagations in thin-layer hBN sheets either supported or suspended by s-SNOM imaging. Then with a high-power broadband IR laser source, we identify two major peaks and multiple auxiliary peaks in the near-field amplitude spectra, obtained using scattering-type near-field FTIR spectroscopy, from both supported and suspended hBN. The major PhP propagation interference peak moves toward the major in-plane phonon peak when the IR illumination moves away from the hBN edge. Specific differences between the auxiliary peaks in the near-field amplitude spectra from supported and suspended hBN sheets are investigated regarding different boundary conditions, associated with edges and substrate interfaces. The outcomes may be explored in heterostructures for advanced nanophotonic applications.

A first modeling approximation of the general performance of radiofrequency (RF) switches based on hexagonal boron nitride (hBN), a two-dimensional (2D) dielectric material is presented. The I-V characteristics intrinsic and extrinsic impedance parameters, the return loss, insertion loss and isolation of RF 2D switches fabricated with hBN are described here by a equivalent circuit models. Straightforward analytical expressions are obtained. In contrast to conventional switches, the unique RF performance of the hBN switch, at ON-state, i.e., a direct improvement with frequency of the insertion loss, is accurately described by considering a capacitor in the intrinsic part of the model. The latter is suggested to be related to storaged charge during the resistive switching mechanism. The highest mean relative error obtained between modeling and measurements of the return loss is of 7.6% with the approach presented here which overcomes the 42.5% of difference obtained with a previous model with an incomplete intrinsic device description.

An efficient single-photon emitter (SPE) should emit photons at a high rate into a well-defined spatio-temporal mode along with an accessible numerical aperture (NA) to increase the light extraction efficiency that is required for effective coupling into optical waveguides. Based on a previously developed experimental approach to fabricate hybrid Fabry–Perot microcavities (Ortiz-Huerta et al. Opt. Express 2018, 26, 33245), we managed to find analytical and finite-difference time-domain (FDTD) values for the, experimentally achievable, geometrical parameters of a hybrid plano-concave microcavity that enhances the spontaneous emission (i.e., Purcell enhancement) of color centers in two-dimensional (2D) hexagonal boron nitride (hBN) while simultaneously limiting the NA of the emitter. Paraxial approximation and a transfer matrix model are used to find the spotsize of the fundamental Gaussian mode and the resonant modes of our microcavity, respectively. A Purcell enhancement of 6 is found for a SPE (i.e., in-plane dipole) hosted by a 2D hBN layer inside the hybrid plano-concave microcavity.

The objective of the present work is to study the mechanical and tribological properties of SiC-hBN such as hardness, density, fracture toughness, friction and wear behavior with and without additives. Therefore, SiC-hBN composite with different composition of hBN (0, 5, 10, and 35 vol. %) and 2 vol.% sintering additive Y2O3 was fabricated by spark plasma sintering at 1800 °C with 55 MPa load for 5 min. under argon atmosphere. SEM–EDS and XRD were used for the microstructural evaluation and characterization of the composite. The hardness of the composite shows a decreasing trend from 19.20 MPa to 16.73 MPa while fracture toughness increases from 2.33 MPa-m1/2 to 3.93 MPa-m1/2, when the hBN volume fraction increases from 5 to 35 vol. % in the composite. The wear and friction behaviour of composites were studied through ball-on-disc wear test rig without lubrication. The wear volume, wear track width, as well as coefficient of friction, decreased by increasing the h-BN volume fraction. The size and shape of debris particles decreased uniformly as the hBN content increases, whereas non-uniformly wear debris was observed in the additive-free composite. The composites with additives showed excellent mechanical and tribological performance as compared to additive-free composites. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride (hBN) has emerged as a key two-dimensional material. Its importance is linked to that of graphene because it provides an ideal substrate for graphene with minimal lattice mismatch and maintains its high carrier mobility. Moreover, hBN has unique properties in the deep ultraviolet (DUV) and infrared (IR) wavelength bands owing to its indirect bandgap structure and hyperbolic phonon polaritons (HPPs). This review examines the physical properties and applications of hBN-based photonic devices that operate in these bands. A brief background on BN is provided, and the theoretical background of the intrinsic nature of the indirect bandgap structure and HPPs is discussed. Subsequently, the development of DUV-based light-emitting diodes and photodetectors based on hBN's bandgap in the DUV wavelength band is reviewed. Thereafter, IR absorbers/emitters, hyperlenses, and surface-enhanced IR absorption microscopy applications using HPPs in the IR wavelength band are examined. Finally, future challenges related to hBN fabrication using chemical vapor deposition and techniques for transferring hBN to a substrate are discussed. Emerging techniques to control HPPs are also examined. This review is intended to assist researchers in both industry and academia in the design and development of unique hBN-based photonic devices operating in the DUV and IR wavelength regions. [ABSTRACT FROM AUTHOR]

The anchoring strength of a nematic liquid crystal, 4-cyano-4'-pentylbiphenyl, is estimated on two-dimensional materials such as graphene, MoS2, and hBN. The changes in brightness attributed to the director rotation at the outer boundary or at the boundary of the orientation domains in the two-dimensional materials are optically observed. Anchoring energy coefficients in the polar and azimuthal directions are estimated by comparing the brightness profile between the experimental observations and numerical calculations. The azimuthal anchoring coefficient is larger than that of polar anchoring for all cases. The polar anchoring of graphite increases with the layer number within 10 layers. The anchoring of graphite is larger than that of MoS2 and hBN flakes. Although restricted results were obtained due to the limitations of the measurement, these results may give hints for understanding the interaction between liquid crystals and two-dimensional materials and can be used for applications. [ABSTRACT FROM AUTHOR]

Single-photon sources are important for integrated photonics and quantum technologies, and can be used in quantum key distribution, quantum computing, and sensing. Color centers in the solid state are a promising candidate for the development of the next generation of single-photon sources integrated in quantum photonics devices. They are point defects in a crystal lattice that absorb and emit light at given wavelengths and can emit single photons with high efficiency. The landscape of color centers has changed abruptly in recent years, with the identification of a wider set of color centers and the emergence of new solid-state platforms for room-temperature single-photon generation. This review discusses the emerging material platforms hosting single-photon-emitting color centers, with an emphasis on their potential for the development of integrated optical circuits for quantum photonics.

Boron vacancy centre ( $V_\textrm{B}^-$ ) ensembles in hexagonal boron nitride (hBN) have attracted recent interest for their potential as two-dimensional solid-state quantum sensors. Irradiation is necessary for $V_\textrm{B}^-$ creation, however, to date only limited attention has been given to optimising the defect production process, especially in the case of bulk irradiation with high-energy particles, which offers scalability through the potential for creating ensembles in large volumes of material. Here we systematically investigate the effect of electron irradiation by varying the dose delivered to a range of hBN samples, which differ in their purity, and search for an optimum in measurement sensitivity. We find that moderate electron irradiation doses ( ${\approx}\,5\times 10^{18}$ cm ^−2 ) appear to offer the best sensitivity, and also observe a dependence on the initial crystal purity. These results pave the way for the scalable and cost-effective production of hBN quantum sensors, and provide insight into the mechanisms limiting $V_\textrm{B}^-$ spin properties.

Industries continue to seek novel eco-friendly additives for developing greases for enhanced tribo-performance and multi-functionality. A lot is reported on the potential of nanoparticles in this aspect, but very limited on the "size effect" of particles, especially on an exploration of hexagonal boron nitride (hBN) particles. In this work, three sizes (micron, sub-micron, and nano) of hBN particles (each ten times bigger than the earlier ones) were used (4 wt.%) in grease to determine the size effect of hBN particles on performance properties, including tribological. Developed greases were examined for tribological properties using a four-ball friction tester, SRV tester, and four-ball EP tester. The results indicated that the greases containing nanoparticles (NPs) of hBN exhibited the best anti-friction (AF), anti-wear (AW), and extreme pressure (EP) properties. These proved more effective as AFA and AWA (~ 60% improvement) rather than EPA (~ 25% improvement) compared to the Li-grease. The morphology and chemical compositions of the films formed on the worn steel balls' surfaces were examined using the scanning electron microscope, EDAX, Raman spectrometer, and 3 D profilometry. Results indicated that easy penetration of smaller-sized hBN particles into the clearance space of a tribo-couple facilitated the formation of beneficial coherent tribo-film that protected the tribo-surfaces, as evident from SEM-EDAX, and Raman data. [ABSTRACT FROM AUTHOR]

In recent years, the hybridization of hyperbolic van der Waals heterostructures with plasmonic two-dimensional nano-materials is one of the interesting research areas at THz frequencies due to the coupled features of the hybrid structure. This article investigates the propagation of tunable surface phonon-plasmon polaritons in grounded hybrid graphene-hexagonal Boron Nitride heterostructures. An analytical model is presented for the proposed structure, by applying the boundary conditions for the electromagnetic components in the various regions, to derive an exact dispersion relation. The structure is simulated and the results are reported in the upper Reststrahlen band. A good agreement is seen between simulation and analytical results, which shows the high accuracy of our mathematical relations. The tunability of the heterostructures is shown by studying the effect of chemical potential on the performance of the structure. A high value of the figure of merit, i.e. FOM = 190, is reported at the frequency of 48.3 THz. The presented study can open the way for the design of novel THz devices for future nano-plasmonic applications. [ABSTRACT FROM AUTHOR]

The field-effect control of the electrical and optical properties of two-dimensional (2D) van der Waals semiconductors (vdW) is one important aspect of this novel class of materials. Thanks to their reduced thickness and decreased screening, electric fields can easily penetrate in a 2D semiconductor and thus modulate their charge density and their properties. In literature, the field effect is routinely used to fabricate atomically thin field-effect transistors based on 2D semiconductors. Apart from the tuning of the electrical transport, it has been demonstrated that the field effect can also be used to modulate the excitonic optical emission of 2D transition metal dichalcogenides such as MoS2 or WSe2. In this paper, we present some recent experiments on the field-effect control of the optical and excitonic properties of the monolayer WS2. Using the deterministic transfer of van der Waals materials, we fabricate planar single-layer WS2 devices contacted by a gold electrode and partially sandwiched between two insulating hexagonal boron nitride (hBN) flakes. Thanks to the planar nature of the device, we can optically access both the hBN encapsulated and the unencapsulated WS2 regions and compare the field-effect control of the exciton population in the two cases. We find that the encapsulation strongly increases the range of tunability of the optical emission of WS2, allowing us to tune the photoluminescence emission from excitons-dominated to trions-dominated. We also discuss how the full encapsulation of WS2 with hBN helps reduce spurious hysteretic effects in the field-effect control of the optical properties, similar to what has been reported for 2D vdW field-effect transistors. [ABSTRACT FROM AUTHOR]

The hybridization of hyperbolic polaritonics with THz plasmonics has attracted immense attention due to its fascinating applications in this region. However, to effectively enhance the performance of these coupled modes, one way is the usage of smart materials in the heterostructures. Here, we introduce a symmetric graphene-based structure containing hexagonal boron nitride (hBN) layers, where two nonlinear layers have been utilized as claddings to improve the confinement of hybrid surface phonon-plasmon-polaritons (HSP3). A new analytical model is derived by using Maxwell's equations and applying the boundary conditions. A set of nonlinear equations are solved numerically, and the obtained results are reported. Harnessing a nonlinear medium together with hybrid graphene-hBN layers allows one to tune the propagation properties of the structure by changing the chemical potential, the relaxation time, and the nonlinear factor. The study has been done for two frequency regions: the upper Reststrahlen and the lower Reststrahlen bands. The numerical results show a long propagation length (Lprop = 300 μm) and a large figure of merit (FOM = 98) for HSP3 propagating in the upper Reststrahlen band at the frequency of 45 THz. The proposed structure and its analytical model can open new insight into the design of tunable devices in mid-infrared plasmonics. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride (hBN) is recognized for its promising application prospects in anti-friction and corrosion resistance due to its self-lubrication and excellent impermeability to gases and liquids. In this study, the TiO 2 -hBN nanocomposite coatings are prepared via the liquid plasma-assisted particle deposition sintering (LPDS) technology, enabling compact and uniform growth of hBN on the Ti6Al4V surface. Results indicate that the dense and stable plasma at the coating/electrolyte interface facilitates the deposition and sintering of hBN particles, effectively filling surface defects and achieving a coating density of 86.7 %. The friction coefficient of the TiO 2 -hBN nanocomposite coating significantly decreases from 0.54 (titanium alloy) to 0.28, remaining stable even after 2000 sliding cycles. Compared to the substrate, the wear rate (4.3 × 10−4 mm3N−1 m−1) of nanocomposite coating drops by 70.8 %, which is primarily attributed to the self-lubricating property of hBN, reducing the frictional shear stress. Moreover, the TiO 2 -hBN nanocomposite coating also has excellent corrosion resistance due to the hBN sheet filling internal defects and inhibiting the corrosion reaction. All these merits render the LPDS technology competitive in expanding the severe service conditions of titanium alloys in aerospace and marine engineering equipment. The TiO 2 -hBN nanocomposite coatings are fabricated via the liquid plasma-assisted particle deposition sintering (LPDS) technology, facilitating the compact and uniform growth of hBN on the Ti6Al4V surface. The composite coating exhibits excellent tribological properties and corrosion resistance. [Display omitted] • TiO 2 -hBN nanocomposite coating is designed to enhance wear and corrosion resistance. • hBN particle is introduced into nanocomposite coating via facile LPDS technology. • The addition of hBN can notably reduce the COF and wear rates of coating. • hBN is conducive to forming a compact coating for enhancing corrosion resistance. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride (hBN), a promising 2D nanomaterial, has potential applications in desalination and osmotic energy harvesting. In all these applications, surface roughness significantly impacts fluid flow in nanomaterial, but its precise effect remains unclear. This creates a knowledge gap in understanding how surface roughness influences water flow at the water-hBN interface, which hinders the development of accurate molecular dynamics (MD) simulations. Here, we address this gap by employing density functional theory (DFT) to calculate atomic charges on rough hBN surfaces. These charges are incorporated into MD simulations, revealing a strong influence on the water-hBN interface. This combined approach accurately predicts experimental water slip length. We further quantify the water flow behavior on hBN using established force fields. Incorporating surface roughness into the model yields results in close agreement with the experimental slip length of ∼ 1 nm for water using FF-2 force fields, validating the simulation approach. Our findings highlight the importance of incorporating realistic surface roughness and force field models in MD simulations of water-nanomaterial interfaces. This work underscores the critical role of accurate 2D material models for understanding fluid flow in nanofluidic applications. [Display omitted] • Surface roughness accurately predicts water slip length (∼ 1 nm) on hBN. • Surface roughness increases friction and reduces slip length on hBN. • Potential to tailor slip length by manipulating roughness. • Close agreement with the experimental slip length of ∼ 1 nm using FF-2 force fields. • Study enhances understanding of nanoscale friction at water-hBN interfaces. [ABSTRACT FROM AUTHOR]

Since the discovery of the quantum Hall effect in 1980, it has attracted intense interest in condensed matter physics and has led to a new type of metrological standard by utilizing the resistance quantum. Graphene, a true two-dimensional electron gas material, has demonstrated the half-integer quantum Hall effect and composite-fermion fractional quantum Hall effect due to its unique massless Dirac fermions and ultra-high carrier mobility. Here, we use a monolayer graphene encapsulated with hexagonal boron nitride and few-layer graphite to fabricate micrometer-scale graphene Hall devices. The application of a graphite gate electrode significantly screens the phonon scattering from a conventional SiO2/Si substrate, and thus enhances the carrier mobility of graphene. At a low temperature, the carrier mobility of graphene devices can reach 3 × 105 cm2/V·s, and at room temperature, the carrier mobility can still exceed 1 × 105 cm2/V·s, which is very helpful for the development of high-temperature quantum Hall effects under moderate magnetic fields. At a low temperature of 1.6 K, a series of half-integer quantum Hall plateaus are well-observed in graphene with a magnetic field of 1 T. More importantly, the ν = ±2 quantum Hall plateau clearly persists up to 150 K with only a few-tesla magnetic field. These findings show that graphite-gated high-mobility graphene devices hold great potential for high-sensitivity Hall sensors and resistance metrology standards for the new Système International d'unités. [ABSTRACT FROM AUTHOR]

Lead (Pb) is commonly used as a X-ray shielding material but has many limitations because of its heaviness and toxicity; thus, it is imperative to be replaced with lightweight and Pb-free shielding materials. To address this problem, molybdenum disulfide (MoS2)/epoxy (MoS2-EP) composites were considered as a possible solution. However, the low compatibility between MoS2 and an epoxy (EP) matrix and an unideal particle dispersion he lack of their distribution have hindered their designed X-ray shielding performance. To overcome this problem, this paper presented how the combination of graphene (GN) and hexagonal boron nitride (hBN) additives can significantly enhance the X-ray shielding performance of MoS2-EP composites. The results showed that when GN or hBN were introduced into the EP-MoS2 composite, X-ray transmission was reduced to 9.8% at 30 kVp and 40.3% at 80 kVp for EP-MoS2-GN and 7.1% at 30 kVp and 34.3% at 80 kVp for EP-MoS2-hBN. These results were explained due to the high aspect ratio of GN, which improved the MoS2 distribution within the EP matrix in the case of hBN, and the electrostatic forces at the interface of hBN and EP leading to better dispersion and interaction with the EP matrix compared to GN. Moreover, by employing an equal amount of the GN–hBN mixture, the synergistic effect of the EP-MoS2-GN-hBN composite film was observed with a significant X-ray shielding enhancement of 52.1% at 30 kVp and 33.2% at 80 kVp compared to that of the EP-MoS2 composite with the same thickness (2 mm) and density. These results were attributed to the molecular bonding of GN or hBN, which improved the compatibility between MoS2 and the EP matrix, providing other benefits of reduced surface roughness (0.46 μm) and improved composite hardness (65.7 HD). This work highlights a new strategy using combined GN and/or hBN for other high atomic number (Z) compounds–polymer composites and the development of advanced non-Pb X-ray shielding applications. [ABSTRACT FROM AUTHOR]

We theoretically studied Dyakonov-like surface polaritons in a hyperbolic crystal covered by a graphene monolayer. From the obtained dispersion equation, four Dyakonov-like surface polariton modes were found, and each mode is a di-hybrid Dyakonov-like surface polariton, namely the surface polaritons of polarization hybridization and plasmon–phonon hybridization. We investigated dispersion properties of these polaritons without damping effect for comparison with the existing results and found a new mode that is a highly localized mode with a large wave number and large attenuation constant. We discussed substantial effects of the graphene layer on the surface polaritons and the dispersion relation in several extreme cases. In a practical case, the dispersion equation with damping effect was further numerically calculated and the propagation distance of the surface polaritons was emphasized. It was found that there are huge differences in propagation distance and dispersion property among the surface polaritons. Our calculation results are based on the graphene-monolayer/hexagonal boron nitride heterostructure. The investigation provides a useful theoretical basis for the nano/micron photonics and technology in the mid-infrared range. [ABSTRACT FROM AUTHOR]

Defects in wide bandgap materials have emerged as promising candidates for solid-state quantum optical technologies. Electrical excitation of single emitters may lead to scalable on-chip devices and therefore is highly sought after. However, most wide bandgap materials are not amenable to efficient doping, posing challenges for electrical excitation and on-chip integration. Here, we demonstrate narrowband electroluminescence from visible and near-infrared color centers in hexagonal boron nitride (hBN). We harness van der Waals tunnel junctions of graphene-hBN-graphene. Charge carriers are electrically injected into hBN, exciting localized defects that emit nonclassical light, as characterized by the second order correlation measurement. Remarkably, the devices operate at room temperature and produce robust, narrowband emission spanning from visible to the near-infrared. Our work marks an important milestone in vdW materials and their promising attributes for integrated quantum technologies and on-chip photonic circuits.