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In this work, we synthesized mixed-phase hexagonal-boron nitride (h-BN)/cubic-BN (c-BN) composites with varying ratios and investigated their frequency and temperature-dependent dielectric properties. As the ratio of c-BN increased, we observed a corresponding increase in the dielectric constant of the composites. Furthermore, we used spark-plasma sintering (SPS) to treat the mixed-phase composite, which resulted in a phase transformation from mixed phase to pure h-BN phase. Remarkably, the composite exhibited an increase in dielectric constant after the SPS process, which can be attributed to the densification of the composite and the enhancement in grain size. Our approach presents a promising strategy for effectively modulating the dielectric properties of BN, which is crucial for advanced electronics. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate the high performance of β-Ga2O3 metal–insulator–semiconductor (MIS) diodes. An ultrathin boron nitride (BN) interlayer is directly grown on the Ga2O3 substrate by pulsed laser deposition. X-ray photoelectron spectroscopy, Raman spectroscopy, and high-resolution transmission electron microscopy confirm the existence of a 2.8 nm BN interlayer. Remarkably, with the insertion of the ultrathin BN layer, the breakdown voltage is improved from 732 V for Ga2O3 Schottky barrier diodes to 1035 V for Ga2O3 MIS diodes owing to the passivated surface-related defects and reduced reverse leakage currents. Our approach shows a promising way to improve the breakdown performance of Ga2O3-based devices for next-generation high-power electronics. [ABSTRACT FROM AUTHOR]

The distinguished properties of hexagonal boron nitride (h -BN), specifically its atomically smooth surface, large critical electric field, and large electronic bandgap, make it ideal for thin film microelectronics and as an ultrawide bandgap semiconductor. Owing to weak van der Waals interactions between layers, h -BN exhibits a significant degree of anisotropic thermal conductivity. The in-plane thermal conductivity of h -BN has extensively been studied, yet the only measured data of cross-plane thermal conductivity ( k ⊥ ) are for exfoliated h -BN films. Exfoliation from bulk crystals is not a sustainable method for scalable production of h -BN due to its low repeatability, low yield, poor control of sample thickness, and limitation to small areas. Thus, it is necessary to investigate the thickness-dependence of k ⊥ for thin films grown by a practical growth method, such as pulsed laser deposition (PLD), which enables the production of reliable and large-area h -BN films with a control of film thickness. We grew h -BN using PLD at 750 °C and observed a decreasing trend of k ⊥ as thickness increases from 30 to 300 nm, varying from ∼1.5 to ∼0.2 W/(m K). We observed a relatively high k ⊥ value for h -BN at a thickness of 30 nm, providing insight into the k ⊥ of PLD-grown films suitable for electronics applications. [ABSTRACT FROM AUTHOR]

Due to adequate properties, bone implant materials have attracted much attention to repair the large-sized bone fractures which cannot be auto-healed. Recently, three-dimensional (3-D) nanocomposites were synthesized using two-dimensional (2-D) materials which reveals unexpected performances. In the present study, 3-D mesoporous biocomposites were developed for bone/dental implant applications. A ternary novel biocomposite system ZrO 2 –MgO-hBN was fabricated with low density, high strength, and mesoporous interconnected architecture using conventional bottom-up synthesis method. Due to remarkable stability in different fluids such as water, minimum essential medium eagle-alpha modification (α-MEM), acids and oils, the fabricated biocomposites displayed multifunctional activities along with suitable proliferation of osteoblast like MG63 cell and filtration of Escherichia coli (E-coli) bacteria from the water. Moreover, the biocomposite exhibited protective nature from harmful ultraviolet (UV) radiation. A new phase of hexagonal boron nitride (h-BN) in the form of highly porous nanotubes was observed that opens the new possibility to optimize the synthesis of porous h-BN nanotubes to explore their further applications. Therefore, based on mechanical, tribological and biological performances, the nanocomposite is a biomimetic material having potential as bone/dental implant and can be used for multifunctional applications. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride (h-BN), graphene oxide (GO) and hybrid (GO/h-BN) nanosheets were employed as fillers in order to enhance the physical properties of the polymer matrix. Composites based in epoxy and these two-dimensional (2D) nanofillers were produced with different wt% and their microstructure, mechanical and thermal properties were investigated. Increases up to 140% in tensile strength, 177% in ultimate strain and 32% in elastic modulus were observed for the hybrid GO/h-BN composite with 0.5 wt% content. The hybrid nanofiller also contributed to the increase up to 142% on thermal conductivity with respect to the pure epoxy for GO/h-BN composite with 2.0 wt% content. Molecular dynamic simulation was used to predict the behavior of possible stacking arrangements between h-BN and GO nanosheets tensioned by normal and shear forces. The results showed that the hybrid GO/h-BN combination can prevent the re-stacking process of exfoliated layers, demonstrating the synergism between these nanostructures with the final effect of better dispersion in the composite material. The excellent thermal and mechanical performance of these hybrid composites engineered by the combination of different types of the 2D inorganic nanoparticles make them multifunctional candidates for advanced materials applications. [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]

Batteries for high temperature applications capable of withstanding over 60 °C are still dominated by primary cells. Conventional rechargeable energy storage technologies which have exceptional performance at ambient temperatures employ volatile electrolytes and soft separators, resulting in catastrophic failure under heat. A composite electrolyte/separator is reported that holds the key to extend the capability of Li-ion batteries to high temperatures. A stoichiometric mixture of hexagonal boron nitride, piperidinium-based ionic liquid, and a lithium salt is formulated, with ionic conductivity reaching 3 mS cm−1, electrochemical stability up to 5 V and extended thermal stability. The composite is used in combination with conventional electrodes and demonstrates to be stable for over 600 cycles at 120 °C, with a total capacity fade of less than 3%. The ease of formulation along with superior thermal and electrochemical stability of this system extends the use of Li-ion chemistries to applications beyond consumer electronics and electric vehicles. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of multifunctional cement and concrete composites filled with hexagonal boron nitride (h-BN) and graphite oxide (GO), is reported and their superior mechanical strength and oil adsorption properties compared to composites devoid of fillers are illustrated. GO is utilized to bridge the cement surfaces while h-BN is used to mechanically reinforce the composites and adsorb the oil. Introduction of these fillers even at low filler weight fractions increases the compressive strength and toughness properties of pristine cement and of porous concrete significantly, while the porous composite concrete illustrates excellent ability for water separation and crude oil adsorption. Experimental results along with theoretical calculations show that such nanoengineered forms of cement based composites would enable the development of novel forms of multifunctional structural materials with a range of environmental applications. [ABSTRACT FROM AUTHOR]

Conventionalwisdom suggests that decreasing dimensions of dielectricmaterials (e.g., thickness of a film) should yield increasing capacitance.However, the quantum capacitance and the so-called “dead-layer”effect often conspire to decrease the capacitance of extremely smallnanostructures, which is in sharp contrast to what is expected fromclassical electrostatics. Very recently, first-principles studieshave predicted that a nanocapacitor made of graphene and hexagonalboron nitride (h-BN) films can achieve superior capacitor properties.In this work, we fabricate the thinnest possible nanocapacitor system,essentially consisting of only monolayer materials: h-BN with grapheneelectrodes. We experimentally demonstrate an increase of the h-BNfilms’ permittivity in different stack structures combinedwith graphene. We find a significant increase in capacitance belowa thickness of ∼5 nm, more than 100% of what is predicted byclassical electrostatics. Detailed quantum mechanical calculationssuggest that this anomalous increase in capacitance is due to thenegative quantum capacitance that this particular materials systemexhibits. [ABSTRACT FROM AUTHOR]

Graphene and hexagonal boron nitride (h-BN) have similar crystal structures with a lattice constant difference of only 2%. However, graphene is a zero-bandgap semiconductor with remarkably high carrier mobility at room temperature, whereas an atomically thin layer of h-BN is a dielectric with a wide bandgap of ?5.9 eV. Accordingly, if precise two-dimensional domains of graphene and h-BN can be seamlessly stitched together, hybrid atomic layers with interesting electronic applications could be created. Here, we show that planar graphene/h-BN heterostructures can be formed by growing graphene in lithographically patterned h-BN atomic layers. Our approach can create periodic arrangements of domains with size ranging from tens of nanometres to millimetres. The resulting graphene/h-BN atomic layers can be peeled off the growth substrate and transferred to various platforms including flexible substrates. We also show that the technique can be used to fabricate two-dimensional devices, such as a split closed-loop resonator that works as a bandpass filter. [ABSTRACT FROM AUTHOR]

Strong in-plane bonding and weak van der Waals interplanarinteractionscharacterize a large number of layered materials, as epitomized bygraphite. The advent of graphene (G), individual layers from graphite,and atomic layers isolated from a few other van der Waals bonded layeredcompounds has enabled the ability to pick, place, and stack atomiclayers of arbitrary compositions and build unique layered materials,which would be otherwise impossible to synthesize via other knowntechniques. Here we demonstrate this concept for solids consistingof randomly stacked layers of graphene and hexagonal boron nitride(h-BN). Dispersions of exfoliated h-BN layers and graphene have beenprepared by liquid phase exfoliation methods and mixed, in variousconcentrations, to create artificially stacked h-BN/G solids. Thesevan der Waals stacked hybrid solid materials show interesting electrical,mechanical, and optical properties distinctly different from theirstarting parent layers. From extensive first principle calculationswe identify (i) a novel approach to control the dipole at the h-BN/Ginterface by properly sandwiching or sliding layers of h-BN and graphene,and (ii) a way to inject carriers in graphene upon UV excitationsof the Frenkell-like excitons of the h-BN layer(s). Our combined approachcould be used to create artificial materials, made predominantly frominter planar van der Waals stacking of robust bond saturated atomiclayers of different solids with vastly different properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • We developed a recyclable SERS substrate for label-free detection of bilirubin. • The LOD of bilirubin was as low as 1.4 × 10−8 M. • The substrate exhibited high detection sensitivity and long-term stability. • The detection of bilirubin in blood samples was realized with a recovery rate of over 80 %. Hyperbilirubinemia refers to an increase in bilirubin (BR) levels and is a serious health concern; in severe cases, hyperbilirubinemia can lead to the death of newborns infants within the first month. Traditional analytical technologies normally involve complex sample pretreatment procedures yet present unsatisfactory detection limits for BR levels. In this study, we developed a recyclable surface-enhanced Raman scattering (SERS) substrate by modifying functional boron nitride (M-BN) monolayer nanosheets on silver nanoarrays (Ag NRs/M-BN) for label-free detection of BR in complex biological samples. Modification of M-BN to silver nanoarrays (Ag NRs) significantly improved the detection sensitivity and long-term stability of the substrate due to the strong surface adsorption ability and thermal stability of M-BN. The limit of detection (LOD) of BR in blood obtained from the Ag NRs/M-BN was as low as 2.5 × 10−8 M, which was attributed to its superior affinity for hydrophobic BR molecules. The spiked blood samples were practically tested with recovery values of around 80 %, and relative standard deviations (RSD) were less than 15 %. The results, combined with the excellent reusability of the as-developed substrates, indicated that the Ag NRs/M-BN substrate provides a simple yet promising platform for nondestructive detection of BR. [ABSTRACT FROM AUTHOR]

Nanocomposites based on graphene oxide (GO), hexagonal boron nitride (h-BN), and their hybrid GO/h-BN as nanofillers in polyurethane (PU) were prepared, and their structures and morphologies were studied. The efficient production of a few layers of nanofillers was completed using the direct liquid-phase exfoliation process. Mechanical and thermal tests were carried out to study the effect of the addition of GO, h-BN, and GO/h-BN at different wt% in the PU system. The tensile strength and Young's modulus showed an increase of up to 85% and 140%, respectively, for the composite containing 0.5 wt% of the hybrid GO/h-BN mixture. An impressive improvement of up to ~1450% in thermal conductivity was observed for the same sample when compared to neat polymer. In order to gain further insights regarding the mechanism behind the nanofiller dispersion and adhesion processes in PU, fully atomistic classical molecular dynamics simulations were carried out. Based on these simulations, it was possible to build structural models that help to explain the thermal and mechanical improvements in the hybrid GO/h-BN composites, with a focus on its stabilization energy. Image 1 • Efficient production of few layers of GO and h-BN was achieved using the direct liquid-phase exfoliation process. • Hybrid GO/h-BN in polyurethane were prepared and studied in their mechanical and thermal properties. • The tensile strength and Young's modulus showed an increase of up to 85% and 140%, respectively for the hybrid composite. • An impressive improvement of 1450% in thermal conductivity was observed for the same sample when compared to neat polymer. • Improvements in these properties suggest that this hybrid system is desirable in composites with multi-functional features. [ABSTRACT FROM AUTHOR]

This study suggests the simple and effective synthesis method of chemically interconnected hexagonal boron nitride (h-BN)–carbon nanotubes (CNTs) hybrid materials (BN–Fe-CNT) with aminosilane functionalized iron oxide nanoparticles (NH 2 –Fe) via amide bond formations. Synthesized BN-Fe-CNT was acting as an effective filler that enhanced the mechanical, thermal, and electrical properties of polyimide (PI) nanocomposites and accelerated polycondensation reaction of poly(amic acid) (PAA) due to its high thermal conductivity and heat diffusivity. At a 2 wt% filler reinforcement, the in-plane thermal conductivity of the BN-Fe-CNT/PI reached 15 W m−1 K−1 at 200 °C, which represents an enhancement of approximately 11430% compared to that of pure PI. Moreover, thermal stability was enhanced from 400 °C to 570 °C. Furthermore, the connected CNTs between the individual h-BN produced electron pathways through the PI matrix, with the BN-Fe-CNT/PI exhibiting 106 times higher electrical conductivity than that of pure PI. The results in this study clearly suggested that the BN-Fe-CNT could be applicable as an effective multi-functional reinforcement in the fabrication of lightweight polymer nanocomposites with superior mechanical properties, high thermal properties, and high electrical conductivities. [ABSTRACT FROM AUTHOR]

Two‐dimensional (2D) materials such as graphene and hexagonal boron nitride (h‐BN) have attracted interest as a conductor/insulator pair in next‐generation devices because of their unique physical properties; however, the thermal transport at the interfaces must be understood to accurately predict the performance of heterostructures composed of these materials. Time‐domain thermoreflectance (TDTR) is used to estimate the thermal boundary conductance (TBC) at the interface of h‐BN and graphene to be 34.5 (+11.6/−7.4) MW m−2 K−1. The advantage of TDTR is that it does not need to create a large temperature gradient at the interface of heterostructures, but it has not yet been used for h‐BN/graphene interface. Phonon transmission and TBC at the h‐BN/graphene interface are predicted by two different formulations of the diffuse mismatch model (DMM) for anisotropic materials. The analysis of phonon transmission and temperature dependence of TBC establishes the flexural branch in the ab‐plane, and the c‐plane longitudinal acoustic branch of graphene and h‐BN are the dominant contributors when implementing both the DMM models. The methodology developed herein can be used to analyze heterostructures of other 2D materials. [ABSTRACT FROM AUTHOR]

Polymer dielectrics find applications in modern electronic and electrical technologies due to their low density, durability, high dielectric breakdown strength, and design flexibility. However, they are not reliable at high temperatures due to their low mechanical integrity and thermal stability. Herein, a self‐assembled dielectric nanocomposite is reported, which integrates 1D polyaramid nanofibers and 2D boron nitride nanosheets through a vacuum‐assisted layer‐by‐layer infiltration process. The resulting nanocomposite exhibits hierarchical stacking between the 2D nanosheets and 1D nanofibers. Specifically, the 2D nanosheets provide a thermally conductive network while the 1D nanofibers provide mechanical flexibility and robustness through entangled nanofiber–nanosheet morphologies. Experiments and density functional theory show that the nanocomposites through thickness heat transfer processes are nearly identical to that of boron nitride due to synergistic stacking of polyaramid units onto boron nitride nanosheets through van der Waals interactions. The nanocomposite sheets outperform conventional dielectric polymers in terms of mechanical properties (about 4–20‐fold increase of stiffness), light weight (density ≈1.01 g cm−3), dielectric stability over a broad range of temperature (25–200 °C) and frequencies (103–106 Hz), good dielectric breakdown strength (≈292 MV m−1), and excellent thermal management capability (about 5–24 times higher thermal conductivity) such as fast heat dissipation. [ABSTRACT FROM AUTHOR]

Quantum dots encompass a broad spectrum of optical, catalytic, and electrochemical properties bringing in novel applications in catalysis, imaging, displays, and optoelectronics. Herein, the unanticipated broad‐spectrum light absorption and high fluorescence quantum yield in fluorinated boron nitride (FBN) quantum dots are discussed. A heterostructure of FBN quantum dots with a wide‐bandgap semiconductor, titania nanotube arrays, exhibits high photocatalytic activity as evidenced by high external quantum efficiency extending from ultraviolet to green region of the solar spectrum (≈24% at 400 nm). The high activity is confirmed using photoelectrochemical hydrogen evolution experiments. Further, it is demonstrated that high fluorescence quantum yield could be tapped for the detection of glycolytic activity in cancer cells compared to normal cells. This finding could shift the paradigm of molecular detection using quantum dots. The 0D structure and the gap states introduced through fluorination are believed to be responsible for these unprecedented characteristics of boron nitride. The synthesis and characterization of the novel material, fluorinated boron nitride quantum dots, are described at length here along with its application in photocatalysis and detection of cancer cells. As a cocatalyst with titania nanotubes, it enhances the photocatalytic activity in the visible region. Optical properties of quantum dots enable the detection of cancer cells with simple laboratory‐scale technique. [ABSTRACT FROM AUTHOR]

The study of two-dimensional (2D) electronic systems is of great fundamental significance in physics. Atomic layers containing hybridized domains of graphene and hexagonal boron nitride (h-BNC) constitute a new kind of disordered 2D electronic system. Magnetoelectric transport measurements performed at low temperature in vapor phase synthesized h-BNC atomic layers show a clear and anomalous transition from an insulating to a metallic behavior upon cooling. The observed insulator to metal transition can be modulated by electron and hole doping and by the application of an external magnetic field. These results supported by ab initio calculations suggest that this transition in h-BNC has distinctly different characteristics when compared to other 2D electron systems and is the result of the coexistence between two distinct mechanisms, namely, percolation through metallic graphene networks and hopping conduction between edge states on randomly distributed insulating h-BN domains. [ABSTRACT FROM AUTHOR]