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Optically active point defects in semiconductors have received great attention in the field of solid-state quantum technologies. Hexagonal boron nitride, with an ultra-wide band gapEg= 6 eV, containing a negatively charged boron vacancy (VB-) with unique spin, optical, and coherent properties presents a new two-dimensional platform for the implementation of quantum technologies. This work establishes the value ofVB-spin polarization under optical pumping with λ ext = 532 nm laser using high-frequency ( ν mw = 94 GHz) electron paramagnetic resonance (EPR) spectroscopy. In optimal conditions polarization was found to be P ≈ 38.4%. Our study reveals that Rabi oscillations induced on polarized spin states persist for up to 30-40 μ s, which is nearly two orders of magnitude longer than what was previously reported. Analysis of the coherent electron-nuclear interaction through the observed electron spin echo envelope modulation made it possible to detect signals from remote nitrogen and boron nuclei, and to establish a corresponding quadrupole coupling constant C q = 180 kHz related to nuclear quadrupole moment of 14 N. These results have fundamental importance for understanding the spin properties of boron vacancy., (© 2024 IOP Publishing Ltd.)

Hydrogen fuel cells based on proton exchange membrane fuel cell (PEMFC) technology are promising as a source of clean energy to power a decarbonized future. However, PEMFCs are limited by a number of major inefficiencies; one of the most significant is hydrogen crossover. In this work, we comprehensively study the effects of two-dimensional (2D) materials applied to the anode side of the membrane as H 2 barrier coatings on Nafion to reduce crossover effects on hydrogen fuel cells, while studying adverse effects on conductivity and catalyst performance in the beginning of life testing. The barrier layers studied include graphene, hexagonal boron nitride (hBN), amorphous boron nitride (aBN), and varying thicknesses of molybdenum disulfide (MoS 2 ), all chosen due to their expected stability in a fuel cell environment. Crossover mitigation in the materials studied ranges from 4.4% (1 nm MoS 2 ) to 46.1% (graphene) as compared to Nafion 211. Effects on proton conductivity are also studied, suggesting high areal proton transport in materials previously thought to be effectively nonconductive, such as 2 nm MoS 2 and amorphous boron nitride under the conditions studied. The results indicate that a number of 2D materials are able to improve crossover effects, with those coated with 8 nm MoS 2 and 1 L graphene able to achieve greater crossover reduction while minimizing conductivity penalty.

Optically addressable high-spin states (S ≥ 1) of defects in semiconductors are the basis for the development of solid-state quantum technologies. Recently, one such defect has been found in hexagonal boron nitride (hBN) and identified as a negatively charged boron vacancy (VB−). To explore and utilize the properties of this defect, one needs to design a robust way for its creation in an hBN crystal. We investigate the possibility of creating VB− centers in an hBN single crystal by means of irradiation with a high-energy (E = 2 MeV) electron flux. Optical excitation of the irradiated sample induces fluorescence in the near-infrared range together with the electron spin resonance (ESR) spectrum of the triplet centers with a zero-field splitting value of D = 3.6 GHz, manifesting an optically induced population inversion of the ground state spin sublevels. These observations are the signatures of the VB− centers and demonstrate that electron irradiation can be reliably used to create these centers in hBN. Exploration of the VB− spin resonance line shape allowed us to establish the source of the line broadening, which occurs due to the slight deviation in orientation of the two-dimensional B-N atomic plains being exactly parallel relative to each other. The results of the analysis of the broadening mechanism can be used for the crystalline quality control of the 2D materials, using the VB− spin embedded in the hBN as a probe.

Increasingly, two-dimensional (2D) materials are being investigated for their potential use as surface-enhanced Raman spectroscopy (SERS) active substrates. Hexagonal Boron Nitride (hBN), a layered 2D material analogous to graphene, is mostly used as a passivation layer/dielectric substrate for nanoelectronics application. We have investigated the SERS activity of few-layer hBN film synthesized on copper foil using atmospheric pressure chemical vapor deposition. We have drop casted the probe molecules onto the hBN substrate and measured the enhancement effect due to the substrate using a 532 nm excitation laser. We observed an enhancement of ≈103 for malachite green and ≈104 for methylene blue and rhodamine 6G dyes, respectively. The observed enhancement factors are consistent with the theoretically calculated interaction energies of MB > R6G > MG with a single layer of hBN. We also observed that the enhancement is independent of the film thickness and surface morphology. We demonstrate that the hBN films are highly stable, and even for older hBN films prepared 7 months earlier, we were able to achieve similar enhancements when compared to freshly prepared films. Our detailed results and analyses demonstrate the versatility and durability of hBN films for SERS applications.

The multiphase co-reinforcing composite combines the advantages of different reinforcing phases to give composite superior properties. In this study, nano-carbon and hexagonal boron nitride (HBN) reinforced Cu-Ti 3 SiC 2 -C composites are fabricated by surface modification, ball milling, vacuum hot pressing (VHP) and hot isostatic pressing (HIP). The content of nano-carbon is 0.5 wt%, and the ratio of multi walled carbon nanotubes (MWCNTs) to graphene was 4:1, 1:1 and 1:4, respectively. Microstructure and mechanical properties of the prepared composites are systematically tested and analyzed. Results show that the interface bonding mode between the reinforcements and matrix is mainly mechanical locking. The composite with the ratio of MWCNTs to graphene is 4:1 shows the best properties in which the hardness, tensile, compressive and shear strength are 121.91 HV, 163.87 MPa, 431.86 MPa and 122.56 MPa, respectively. The reinforcements improve the properties of composites by the mechanisms of load transfer, fine grain strengthening, particle strengthening and anti-friction lubrication. [ABSTRACT FROM AUTHOR]

In the present study, the feasibility of fabricating an Ni(Cr)/hBN self-lubricating nanocomposite by mechanical alloying technique was studied. To achieve this goal, a Ni–20 wt % Cr powders mixture was first milled up to 40 h to produce the nanostructured Ni(Cr) solid solution. hBN particles were subsequently added to Ni(Cr) and further mixed for 3 h. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM) were performed to study phase transformations and microstructural evolutions during the milling process. The results showed that the dissolution of Cr in Ni started after 5 h and completed after 30 h of mechanical alloying. TEM studies also showed that the 40 h milled Ni(Cr) solid solution had the average grain size of 50 nm. Miedema's semi-empirical thermodynamic model was used to predict the most stable phases in the Ni–Cr binary system. The results showed that the Gibbs free energy change of solid solution formation (–8.44 kJ/mol) was much lower than that of the amorphous phase (–1.3 kJ/mol) in the chemical composition of Ni–20 wt % Cr, thereby confirming the experimental results. The formation of a fine lamellar structure during the milling process was found to be the main reason for the solid solution formation. The nanostructured Ni(Cr) solid solution showed suitable thermal stability at 800°C. It was also observed that hBN particles were homogenously distributed in the as-fabricated Ni(Cr) after 3 h of mixing. The results of the present study also revealed that the mechanical alloying process could be regarded as a high-potential technique for the fabrication of metal-based self-lubricating composites. [ABSTRACT FROM AUTHOR]

Abstract Hexagonal boron nitride (hBN), also called as white graphite is known to exhibit excellent combination of thermal, thermo-physical, mechanical and tribological properties as a filler (solid lubricant). Not much reported on its potential as nano-particles. In this study, micro and nanocomposites of hBN were prepared with the combination of polyaryl ether ketone (PAEK) as a matrix (50%), short glass fibers (GF) (30%) as a reinforcement and natural graphite (10%) as a primary solid lubricant (SL) apart from hBN particles (10%) as a secondary SL. The micro-composite (MC) and nano-composite (NC) contained hBN particles in micron size and combination of micron and nano size (7 and 3%) respectively. The NC exhibited enhanced mechanical and tribological performance compared to the MC. Tribological tests were performed on a pin-on-disc tribometer under dry sliding regime to evaluate PV limit (pressure x velocity) values. Influence of load and sliding speed on the friction coefficient (μ) and specific wear rate (K 0) on the composites was investigated. The composites showed PV limit of 100 MPa m/s along with μ in the range of 0.04–0.08 and K 0 in the range of 2.5–7 × 10− 16 m 3 /Nm. It was also found that the superior performance of NC was due to more efficient, thin and coherent film transferred on the disc. Moreover, structural and morphological changes were studied with Raman spectroscopy and scanning electron microscopy (SEM). Wear mechanism of the worn surfaces were discussed using XPS (X-ray photoelectron spectroscopy). Highlights • Hexa boron nitride (hBN) showed better lubricating characteristics in combination with graphite. • The glass fibers were oriented along the direction of polymer melt which was explained by X-ray tomography. • Nano-hBN and graphite has synergistic effect on improving tribological behavior and PV limit of composites up to 100 MPa m/s. [ABSTRACT FROM AUTHOR]

Abstract WC-Co cermets (ceramic-metal composites) were ground by a resin bonded diamond grinding wheel using hexagonal boron nitride (hBN) nano-aerosol to improve the grindability. This is a new generation grinding fluid and was produced by dispersing nano-sized hBN platelets in deionized water. Small quantity cooling-lubrication (SQCL) technology was employed to deliver hBN nanofluid in the form of nano-aerosol so that volumetric consumption rate could be kept at a very low value of 200 ml/h. The nanofluid, when separately characterized, demonstrated good lubrication and heat dissipation capability in reference with soluble oil, which is a commonly used cutting fluid for grinding. The superior tribological characteristics of hBN nanofluid were more pronounced at a high sliding speed of 1 m/s, as observed during a ball-on-disc test. However, the beneficial effect of using hBN nanofluid could be extracted more efficiently only in aggressive grinding condition. A clear drop in specific energy, favourable values of residual stress indicate the same. Prevalence of low grinding zone temperature was reflected through low specific energy values and finer but complex chip micromorphology. Overall the aqueous hBN nanofluid was proven to be a high performing grinding fluid suitable for SQCL application and WC-Co cermet grinding. Highlights • Grindability of WC-Co cermet is improved using hBN nano-aerosol. • hBN nano-aerosol is more effective at aggressive sliding conditions in ball-on-disc test. • Heat dissipation capability of hBN aerosol is much superior to that of soluble oil. • Specific energy and residual stress studies indicate the supremacy of hBN over soluble oil aerosol. • Nano-aerosol of hBN produced fragmented grinding chips having distortion of Co-matrix around micro grains of WC. [ABSTRACT FROM AUTHOR]

Layered materials are very attractive for studies of light–matter interactions at the nanoscale. In particular, isolated quantum systems such as color centers and quantum dots embedded in these materials are gaining interest due to their potential use in a variety of quantum technologies and nanophotonics. Here, we review the field of nonclassical light emission from van der Waals crystals and atomically thin two-dimensional materials. We focus on transition metal dichalcogenides and hexagonal boron nitride and discuss the fabrication and properties of quantum emitters in these systems and proof-of-concept experiments that provide a foundation for their integration in on-chip nanophotonic circuits. These experiments include tuning of the emission wavelength, electrical excitation, and coupling of the emitters to waveguides, dielectric cavities, and plasmonic resonators. Finally, we discuss current challenges in the field and provide an outlook to further stimulate scientific discussion. [ABSTRACT FROM AUTHOR]

An efficient method of lubrication and cooling for green machining is nanofluid minimum quantity lubrication (NMQL). Compared to other vegetable-based oils, coconut oil has the highest viscosity index, lubricity, and oxidative characteristics, making it a popular trending lubricant for decreasing friction. However, its performance at higher temperatures degrades owing to higher saponification value. In order to improve its performance, the solid nano-friction modifier (hBN) is dispersed in it, and the colloid is called a nanofluid. UV–Vis–NIR spectrophotometer, HR-TEM, and FTIR spectroscopy characterize nanofluid. The stability of nanofluid at 0.3 vol% of hBN has been observed to be the highest compared to other volume fractions. Compared to coconut oil, prepared nanofluid is superior in terms of increased thermal conductivity, thermal stability, and viscosity for all the tested temperature ranges. Nanofluid shows increased viscosity index (VI) by 20%, reduced contact angle by 45%, and lower coefficient of friction (COF) by 32% compared to coconut oil. Further performance of this modified biodegradable nanofluid under Minimum quantity lubrication (MQL) on end milling of Incoloy 925 has been studied. In order to compare the machining performance under different cutting environments, cutting temperature, cutting force, specific cutting energy, power consumption, carbon emission, chip morphology, surface topology/topography, and tool wear were evaluated. Finally, sustainability assessments for different cutting environments have been performed. Biodegradable oil-based NMQL-assisted machining has performed better than dry and MQL-assisted machining. [Display omitted] [ABSTRACT FROM AUTHOR]

Hexagonal boron nitrite (hBN) is an attractive material for many applications such as in electronics as a complement to graphene, in anti-oxidation coatings, light emitters, etc. However, the synthesis of high-quality hBN at cost-effective conditions is still a great challenge. Thus, this work reports on the synthesis of large-area and crystalline hBN nanosheets via the modified polymer derived ceramics (PDCs) process. The addition of both the BaF2 and Li3N, as melting-point reduction and crystallization agents, respectively, led to the production of hBN powders with excellent physicochemical properties at relatively low temperatures and atmospheric pressure conditions. For instance, XRD, Raman, and XPS data revealed improved crystallinity and quality at a decreased formation temperature of 1200 °C upon the addition of 5 wt% of BaF2. Moreover, morphological determination illustrated the formation of multi-layered nanocrystalline and well-defined shaped hBN powders with crystal sizes of 2.74−8.41 ± 0.71 µm in diameter. Despite the compromised thermal stability, as shown by the ease of oxidation at high temperatures, this work paves way for the production of large-scale and high-quality hBN crystals at a relatively low temperature and atmospheric pressure conditions.

Micro/nanoscale design of composite materials enables alteration of their properties for advanced functional materials. One of the biggest challenges in material design is the controlled decoration of composite materials with the desired functional additives. This study reports on and demonstrates the homogeneous decoration of hexagonal boron nitride (hBN) on poly(methylmethacrylate) (PMMA) and vice versa. The formation of the composite materials was conducted via a low environmental load and a low-energy-consuming, electrostatic nano-assembly method which also enabled the efficient usage of nano-sized additives. The hBN/PMMA and PMMA/hBN composites were fabricated in various size combinations that exhibited percolated and layer-oriented structures, respectively. The thermal conductivity behaviors of hBN/PMMA and PMMA/hBN composites that exhibited good microstructure were compared. The results showed that microstructural design of the composites enabled the modification of their heat-conducting property. This novel work demonstrated the feasibility of fabricating heat-conductive PMMA matrix composites with controlled decoration of hBN sheets, which may provide a platform for further development of heat-conductive polymeric materials.

Distributed Bragg Reflectors (DBR) are well-established photonic structures that are used in many photonic applications. However, most of the DBRs are based on different materials or require post-process etching which can hinder integration with other components in the final photonic structure. Here, we demonstrate the fabrication of DBR structures consisting only of undoped boron nitride (BN) layers with high refractive index contrast by using metal-organic chemical vapor deposition (MOCVD). This has been achieved in a single process, without the need for any post-process etching. The difference in the refractive index of the component BN layers stems from different degrees of porosity of the individual BN layers, which is a direct result of a different growth temperature. The fabricated DBR structures consist of 15.5 pairs of BN layers and exhibit a reflectance of 87 ± 1% at the maximum. The wavelength of maximum reflectance can be tuned from 500 nm up to the infrared region (IR), by simply adjusting the growth periods of subsequent BN layers. We also demonstrate that the fabricated structures can be used to create an optical microcavity. The fabricated DBRs are very promising candidates for future applications, for example in combination with single-photon emitters in h-BN, which could allow the building of a cavity-based all-BN single-photon source., (Creative Commons Attribution license.)

Two high-temperature solid lubricants, CaF 2 and hBN, were added respectively into Fe-based impregnated diamond bit matrix to fabricate self-lubricating specimens of various lubricant contents by powder metallurgy method. Mechanical and tribological tests were performed on the specimens to investigate the relationship between specimen properties and lubricant content. The microstructure of the cross sections and the morphology of the worn surfaces of the specimens were analyzed using scanning electron microscopy (SEM). The results showed that the increase in solid lubricant content had a general weakening effect on the mechanical properties of the specimens, while such effect of CaF 2 was less significant than that of hBN. The hardness of CaF 2 specimens was found increasing slightly with CaF 2 content. Improved lubricity on the sliding surfaces was observed, while the wear resistance of the two specimens behaved differently. SEM analysis showed different microstructures of the two specimens, and improved wear condition for the CaF 2 specimen. However, the worn surface of the hBN specimen was found deteriorated. [ABSTRACT FROM AUTHOR]

In this study, the effect of temperature on the SiC grain size was investigated in the synthesis of hexagonal boron nitride-silicon carbide (hBN-SiC) composites. Samples were sintered at 1700oC, 1800oC, 1900oC and 2000oC, under 50MPa pressure for 15 minutes by spark plasma sintering (SPS). In order to determine the effect of sintering temperature on the SiC grain size, grain sizes were measured by ImageJ program. Grain size distributions were determined by using normal distribution function. When the temperature was increased from 1700°C to 1900°C, the amount of h-BN increased by 0.9% and remained unchanged at 2000°C. When the temperature was increased from 1700°C to 2000°C, the average grain size of SiC increased from 1.9 μm to 1.96 μm. The standard deviation values of grain size distribution increased from 0,445 at 1700°C to 0,812 at 2000°C. Depending on the temperature, the grain size distribution has increased. Due to the strong covalent bonds and plate-like structure of hBN, it has poor sinterability. Because of this feature, it can be said that the growth of SiC grains is slowed down by hBN. [ABSTRACT FROM AUTHOR]

The development of combined anticancer therapeutic techniques has drawn increased attention for enhanced therapeutic efficacy. In this work, we synthesized Near Infrared (NIR) responsive ICG (I) functionalized hexagonal boron-nitride (hBN) as photothermal therapeutic agent (hBNI) and Doxorubicin (Dox)-conjugated Hyaluronic acid (HA) as tumor targeted chemotherapeutic agent (d-HA-Dox). Using adhesion properties of Dopamine (d), the hBNI has been integrated with d-HA-Dox to make a tumor targeted photothermal chemotherapeutic agent (hBNI/d-HA-Dox). The nanostructure of hBNI/d-HA-Dox has been studied using 1H NMR, FTIR, UV–vis-NIR and AFM images. Our in vitro results have provided evidence that hBNI/d-HA-Dox can efficiently damage targeted cancer cells while healthy cells are less affected suggesting that the targeted hBNI/d-HA-Dox nanoparticles work as a complementary antitumor agent with its synergistic co-therapeutic power. [ABSTRACT FROM AUTHOR]

Chemical vapor deposition (CVD) has been established as the most effective way to grow large area two-dimensional materials. Direct study of the etching process can reveal subtleties of this competing with the growth reaction and thus provide the necessary details of the overall growth mechanism. Here we investigate hydrogen-induced etching of hBN and graphene and compare the results with the classical kinetic Wulff construction model. Formation of the anisotropically etched holes in the center of hBN and graphene single crystals was observed along with the changes in the crystals' circumference. We show that the edges of triangular holes in hBN crystals formed at regular etching conditions are parallel to B-terminated zigzags, opposite to the N-terminated zigzag edges of hBN triangular crystals. The morphology of the etched hBN holes is affected by a disbalance of the B/N ratio upon etching and can be shifted toward the anticipated from the Wulff model N-terminated zigzag by etching in a nitrogen buffer gas instead of a typical argon. For graphene, etched hexagonal holes are terminated by zigzag, while the crystal circumference is gradually changing from a pure zigzag to a slanted angle resulting in dodecagons. [ABSTRACT FROM AUTHOR]

Magnetic doping of 2D materials such as Transition Metal Dichalcogenides is promising for enhancement of magneto-optical properties, as it was previously observed for 3D diluted magnetic semiconductors. To maximize the effect of magnetic ions, they should be incorporated into the crystal lattice of 2D material rather than form separated precipitates. This work shows study on incorporating magnetic manganese ions into the MoSe 2 monolayers using molecular beam epitaxy. We test growth on various substrates with very different properties: polycrystalline SiO 2 on Si, exfoliated 2D hexagonal Boron Nitride flakes (placed on SiO 2 /Si), monocrystalline sapphire, and exfoliated graphite (on tantalum foil). Although atomic force microscopy images indicate presence of MnSe precipitates, but at the same time, various techniques reveal effects related to alloying MoSe 2 with Mn: Raman scattering and photoluminescence measurements shows energy shift related to presence of Mn, scanning transmission microscopy shows Mn induced partial transformation of 1H to 1T' phase. Above effects evidence partial incorporation of Mn into MoSe 2 layer. [ABSTRACT FROM AUTHOR]

• hBN-based thermal regulation by adjusting its shift frequency is investigated. • Adjustable hyperbolic modes can couple and decouple with surface polaritons. • Regulation ratios reach 159.6 for hBN plates, and > 2 for SiC/hBN and G/hBN plates. Nanoscale thermal regulation plays a vital role in many applications, especially in highly-integrated electronics. In this study, we theoretically analyze the near-field radiation heat transfer within hBN-based planar systems, including bare hBN plates, SiC/hBN plates, graphene/hBN plates and Au/hBN plates. We predict that tailoring the shift frequency of phonon could alter the hyperbolic modes (HMs) of hBN, thus allowing for the coupling and decoupling of HMs with SPhPs of SiC and GSPPs of graphene. Therefore, the radiative heat flux in hBN-based systems except for Au/hBN plates can be greatly regulated, and the regulation ratio can reach 159.6 for bare hBN plates, and above 2 for SiC/hBN plates and for graphene/hBN plates. Results may facilitate understanding of the principles of hBN-based evanescent wave coupling and nanoscale thermal management. [ABSTRACT FROM AUTHOR]

In this paper we demonstrate a metal organic chemical vapor deposition (MOCVD) process for growth of few layer hBN films on Ni(111) on sapphire substrates using triethylborane (TEB) and ammonia (NH3). Ni(111) was selected as a substrate due to its symmetry and close lattice matching to hBN. Using atomic force microscopy (AFM) we find hBN is well aligned to the Ni below with in plane alignment between the hBN zig zag edge and the of Ni. We further investigate the growth process exploring interaction between precursors and the Ni(111) substrate. Under TEB pre-exposure Ni-B and graphitic compounds form which disrupts the formation of layered phase pure hBN; while NH3 pre-exposure results in high quality films. Tunnel transport of films was investigated by conductive-probe AFM demonstrating films to be highly resistive. These findings improve our understanding of the chemistry and mechanisms involved in hBN growth on metal surfaces by MOCVD.

The Drosophila homeodomain-interacting protein kinase (Hipk) is the fly representative of the well-conserved group of HIPKs in vertebrates. It was initially found through its characteristic interactions with homeodomain proteins. Hipk is involved in a variety of important developmental processes, such as the development of the eye or the nervous system. In the present study, we set Hipk and the Drosophila homeodomain proteins Homeobrain (Hbn), Empty spiracles (Ems), and Muscle segment homeobox (Msh) in an enzyme-substrate relationship. These homeoproteins are transcription factors that function during Drosophila neurogenesis and are, at least in part, conserved in vertebrates. We reveal a physical interaction between Hipk and the three homeodomain proteins in vivo using bimolecular fluorescence complementation (BiFC). In the course of in vitro phosphorylation analysis and subsequent mutational analysis we mapped several Hipk phosphorylation sites of Hbn, Ems, and Msh. The phosphorylation of Hbn, Ems, and Msh may provide further insight into the function of Hipk during development of the Drosophila nervous system.

The growth of hexagonal boron nitride, hBN, on Ir(111) at 1150–1200 K by thermal decomposition of borazine has been monitored in situ by means of low energy electron microscopy, LEEM. A major and unexpected hBN growth induced transformation of the step morphology on Ir(111) is observed. The dominant orientation of the steps evolves persistently from 〈1–10〉 during the initial experiment(s), towards 〈11–2〉 after numerous experiments. The latter orientation was established directly from an involved analysis of the profile of the specular beam in a selected area diffraction pattern. Images of the hBN islands grown on surface regions with dominant 〈1–10〉 steps reveal that the hBN edges are oriented along 〈1–10〉 and 〈11–2〉 directions in about equal abundance. Using the direct ascertainment of the step orientations we are able to identify unequivocally the nature of the edges of individual hBN islands on areas with predominant 〈11–2〉 steps as solely of the armchair type. This assessment consolidates both the major evolution of the step morphology from 〈1–10〉 into dominant 〈11–2〉 steps during hBN growth on Ir(111) and the earlier reported alignment of the moiré pattern with the substrate.

Van der Waals heterostructures have great potential in large-scale integration devices and exploration of new physics. Experimental investigations allow flexible combinations of two-dimensional crystals in device fabrications. Theory, however, has limitations of supercell sizes and commensurability, translated into computational effort. In this work, we demonstrate the application of the coincidence lattice method to simulate two $$\hbox {hBN/MoSe}_2$$ heterobilayers taking interlayer twist effects into account. We predict that both systems are stable upon contact and interact via van der Waals dispersions. We found that electronic properties of $$\hbox {MoSe}_2$$ are preserved for both simulated systems, but hBN suffers from the increase of interface interactions, as evidenced by band structures and density of states calculations. Finally, band discontinuities are obtained and charge transfer arguments explain small shifts in band offsets with respect to natural alignments. We conclude that hBN is a reasonable substrate for preserving useful properties of $$\hbox {MoSe}_2$$ for application in electronic and optoelectronic devices, and that interlayer twist angles play a significant role in the physics of van der Waals heterostructures. [ABSTRACT FROM AUTHOR]

Graphene and some graphene like two dimensional materials; hexagonal boron nitride (hBN) and silicene have unique mechanical properties which severely limit the suitability of conventional theories used for common brittle and ductile materials to predict the fracture response of these materials. This study revealed the fracture response of graphene, hBN and silicene nanosheets under different tiny crack lengths by molecular dynamics (MD) simulations using LAMMPS. The useful strength of these two dimensional materials are determined by their fracture toughness. Our study shows a comparative analysis of mechanical properties among the elemental analogues of graphene and suggested that hBN can be a good substitute for graphene in terms of mechanical properties. We have also found that the pre-cracked sheets fail in brittle manner and their failure is governed by the strength of the atomic bonds at the crack tip. The MD prediction of fracture toughness shows significant difference with the fracture toughness determined by Griffth's theory of brittle failure which restricts the applicability of Griffith's criterion for these materials in case of nano-cracks. Moreover, the strengths measured in armchair and zigzag directions of nanosheets of these materials implied that the bonds in armchair direction have the stronger capability to resist crack propagation compared to zigzag direction. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride ( hBN), a two-dimensional nanofiller with good mechanical properties, high thermal conductivity and excellent lubrication properties, has the potential to substantially reinforce polymers to form nanocomposites with advanced properties. In this study, we successfully prepared hBN nanosheets with a thickness of a few atoms by using amine-capped aniline trimer ( AT) as dispersant. Epoxy/ hBN nanocomposites were prepared by curing reaction of epoxy E51, Jeffamine D230 and AT-modified hBN nanosheets, where the hBN contents were 0.5, 1, 2 and 4 wt%. An increase in contact angle of the epoxy/ hBN nanocomposites was evident in the presence of hBN nanosheets, implying an increase in the hydrophobic nature of the composites. The as-prepared composites exhibited enhanced mechanical and tribological performance compared to pure epoxy resin. This effectiveness in improving the mechanical, friction and wear behavior of the epoxy composites could be attributed to the complementary action of excellent mechanical properties, lubrication and thermal conductivity of hBN nanofillers. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The production of self-lubricating composites containing second phase particles is one of the most promising choices for controlling friction and wear in energy efficient modern systems. To gain a better understanding of the wear behaviour of such materials, Fe-Si-C matrix composites containing solid lubricants added during the mixing step were studied in this work. The samples were produced using powder metallurgy route, with total contents of 5, 7.5 and 10% in terms of volume of hexagonal boron nitride (hBN) and graphite mixtures as the solid lubricants. The composite's tribological properties were evaluated under reciprocating sliding conditions and their mechanical properties were tested using tensile tests. Additionally, after interruptions at different stages of the reciprocating tests, the wear scars were characterised by Raman spectroscopy and scanning electronic microscopy, to evaluate the evolution of the wear with test time. Higher total solid lubricant contents greatly increased the scuffing resistance of the composites, but decreased the mechanical properties. Furthermore, increasing the hBN content reduced both properties. Among the composites studied, the samples containing 1% vol hBN and 9% vol graphite showed the best combination of mechanical and tribological properties. [ABSTRACT FROM AUTHOR]

2D atomic crystals such as single layer graphene (SLG) and hexagonal boron nitride (hBN) have been shown to be 'unexpectedly permeable' to hydrogen ions under ambient conditions with the proton conductivity rising exponentially with temperature. Here, the first successful addition of SLG made by a chemical vapor deposition (CVD) method is shown to an operational direct methanol fuel cell significantly enhancing the performance of the cell once the temperature is raised above 60 °C, the temperature at which the proton conductivity of SLG is higher than the Nafion membrane on which it is mounted. Above this temperature, the resistance to proton transport of the system is not affected by the graphene but the barrier properties of graphene inhibit methanol crossover. The performance of the fuel cell is shown to increase linearly with coverage of SLG above this temperature. Results show that the maximum power density is increased at 70 °C by 45% in comparison to the standard membrane electrode assembly without graphene. In addition, a membrane with CVD hBN shows enhanced performance across the entire temperature range due to better proton conductivity at lower temperatures. [ABSTRACT FROM AUTHOR]

The commonly used diagnostic methods for liver malignancies are core needle biopsy (CNB), fine needle aspiration cytology (FNAC), and touch imprint (TIC), but these methods have contradictory and uncertain results. We investigate a plasmon biosensor that uses a hBN ring structure coupled with a silver rectangular square ring to identify healthy cells and metastatic cancer cells in liver cells. We study the influence of the structure's output characteristics and geometric parameters on the plasmon resonance. The results show that the designed structure can achieve refractive index sensitivity up to 920 nm / RIU, and the maximum quality factor is 58RIU-1 when the change of the sensing medium refractive index Δn = 0.4. Our method showed good spectral response to non-cancerous (NMET) and metastatic (MET) cancerous liver tissue cells. The device has broad application prospect in plasma sensing and absorber design. [ABSTRACT FROM AUTHOR]

Graphene-hexagonal boron nitride (hBN) scalable heterostructures are pivotal for the development of graphene-based high-tech applications. In this work, we demonstrate the realization of high-quality graphene-hBN heterostructures entirely obtained with scalable approaches. hBN continuous films were grown via ion beam-assisted physical vapor deposition directly on commercially available SiO 2 /Si and used as receiving substrates for graphene single-crystal matrixes grown by chemical vapor deposition on copper. The structural, chemical, and electronic properties of the heterostructure were investigated by atomic force microscopy, Raman spectroscopy, and electrical transport measurements. We demonstrate graphene carrier mobilities exceeding 10,000 cm 2 /Vs in ambient conditions, 30% higher than those directly measured on SiO 2 /Si. We prove the scalability of our approach by measuring more than 100 transfer length method devices over a centimeter scale, which present an average carrier mobility of 7500 ± 850 cm 2 /Vs. The reported high-quality all-scalable heterostructures are of relevance for the development of graphene-based high-performing electronic and optoelectronic applications.

Negatively charged boron vacancies (V B ) in hexagonal boron nitride (hBN) have recently gained interest as spin defects for quantum information processing and quantum sensing by a layered material. However, the boron vacancy can exist in a number of charge states in the hBN lattice, but only the -1 state has spin-dependent photoluminescence and acts as a spin-photon interface. Here, we investigate the charge state switching of V - ) in hexagonal boron nitride (hBN) have recently gained interest as spin defects for quantum information processing and quantum sensing by a layered material. However, the boron vacancy can exist in a number of charge states in the hBN lattice, but only the -1 state has spin-dependent photoluminescence and acts as a spin-photon interface. Here, we investigate the charge state switching of V B defects under laser and electron beam excitation. We demonstrate deterministic, reversible switching between the -1 and 0 states (V B - ), occurring at rates controlled by excess electrons or holes injected into hBN by a layered heterostructure device. Our work provides a means to monitor and manipulate the V B 0 + e - ), occurring at rates controlled by excess electrons or holes injected into hBN by a layered heterostructure device. Our work provides a means to monitor and manipulate the V B charge state, and to stabilize the -1 state which is a prerequisite for spin manipulation and optical readout of the defect.

Electron tunneling spectroscopy measurements on van der Waals heterostructures consisting of metal and graphene (or graphite) electrodes separated by atomically thin hexagonal boron nitride tunnel barriers are reported. The tunneling conductance, dI/dV, at low voltages is relatively weak, with a strong enhancement reproducibly observed to occur at around ∣V∣ ≈ 50 mV. While the weak tunneling at low energies is attributed to the absence of substantial overlap, in momentum space, of the metal and graphene Fermi surfaces, the enhancement at higher energies signals the onset of inelastic processes in which phonons in the heterostructure provide the momentum necessary to link the Fermi surfaces. Pronounced peaks in the second derivative of the tunnel current, d2I/dV2, are observed at voltages where known phonon modes in the tunnel junction have a high density of states. In addition, features in the tunneling conductance attributed to single electron charging of nanometer-scale defects in the boron nitride are also observed in these devices. The small electronic density of states of graphene allows the charging spectra of these defect states to be electrostatically tuned, leading to "Coulomb diamonds" in the tunneling conductance. [ABSTRACT FROM AUTHOR]