Synthesis and Modification of Boron Nitride nanotubes using ion implantation.

In this work, Chemical Vapour Deposition (CVD) has been used to synthesize boron nitride (BN) nanostructures, particularly nanotubes, and selectively introduce defects into the lattice of the synthesized BN nanostructures through ion implantation. Scanning electron microscopy (SEM) images show clear evidence of BN nanostructures and BN nanotubes (BNNTs), with the latter appearing as long, thin structures with diameters ranging from ⁓30-80 nm. Raman analysis show an E2g mode of vibration assigned to hexagonal BN (h-BN) at 1366 cm-1 after ion implantation, with increased intensity. Grazing incidence X-ray diffraction (GIXRD) spectra revealed a prominent peak between 54 and 56°, corresponding to the (004) h-BN reflection, which was used to determine the average lattice parameter c⁓0.662 nm representing the stacking direction of the BN layers. The majority of the samples had broad peaks, indicative of a nanocrystalline material. The only exception was the sample grown at 1200 °C, which was found to have a Scherrer crystallite size >100 nm. In contrast, the rest of the samples had an average size of 3.5 nm. Notable observations in this study include a significant rise in the size of the Raman derived crystallite domains in the nanostructures synthesized at 1100 and 1200 °C after ion implantation with boron ions at fluence 5 × 1014 ions/cm2.

Natural Deep Eutectic Solvent-Assisted Construction of Silk Nanofibrils/Boron Nitride Nanosheets Membranes with Enhanced Heat-Dissipating Efficiency.

Natural polymer-derived nanofibrils have gained significant interest in diverse fields. However, production of bio-nanofibrils with the hierarchical structures such as fibrillar structures and crystalline features remains a great challenge. Herein, an all-natural strategy for simple, green, and scalable top-down exfoliation silk nanofibrils (SNFs) in novel renewable deep eutectic solvent (DES) composed by amino acids and D-sorbitol is innovatively developed. The DES-exfoliated SNFs with a controllable fibrillar structures and intact crystalline features, novelty preserving the hierarchical structure of natural silk fibers. Owing to the amphiphilic nature, the DES-exfoliated SNFs show excellent capacity of assisting the exfoliation of several 2D-layered materials, i.e., h-BN, MoS2, and WS2. More importantly, the SNFs-assisted dispersion of BNNSs with a concentration of 59.3% can be employed to construct SNFs/BNNSs nanocomposite membranes with excellent mechanical properties (tensile strength of 416.7 MPa, tensile modulus of 3.86 GPa and toughness of 1295.4 KJ·m-3) and thermal conductivity (in-plane thermal conductivity coefficient of 3.84 W·m-1·K-1), enabling it to possess superior cooling efficiency compared with the commercial silicone pad.

"Surface-Like Growth" Strategy for the Direct Synthesis of Horizontally Aligned Boron Nitride Nanotubes.

The inherent properties of boron nitride nanotubes (BNNTs) can be further enhanced through the control of their anisotropy. In particular, horizontally aligned BNNTs (HABNNTs) exhibit considerable potential for various applications. However, directly synthesizing HABNNTs is difficult owing to the random floating of BNNTs and the absence of directional forces. Here, we employed a simple, efficient, and universal "surface-like growth" strategy to synthesize high-density and high-quality HABNNTs in the W2B5/Zn precursor system. First, the floating range of BNNTs was restricted to the vicinity of the precursor, and then, directional forces were applied to induce BNNT directional growth along the substrate surface. Experiments and simulations confirmed that the HABNNT orientation could be controlled through manipulation of the directional forces. Furthermore, the strategy was employed for HABNNTs synthesis using the MoB2/Zn, further demonstrating the universality of the approach. Overall, this work offers a fresh perspective on the synthesis of HABNNTs, further expanding their potential applications.

Harnessing synergy: Polydopamine-hBN integration in electrospun nanofibers for Co (II) ion, methylene blue and crystal violet dyes adsorption.

In today's world, major pollutants, such as cationic dyes and heavy metals, pose a serious threat to human health and the environment. In this study, a novel adsorbent was created through the electrospinning of polyvinyl alcohol/polyacrylic acid (PVA/PAA), incorporated with hexagonal boron nitride (hBN) coated with polydopamine (PDA). The integration of hBN and PDA substantially enhanced the adsorption capacity of the PVA/PAA fibers, making them highly effective in adsorbing cationic dyes such as methylene blue and crystal violet, as well as cobalt (II) ions, from contaminated water. The adsorbents were assessed to understand how their adsorption behavior varies with pH, as well as to examine their adsorption kinetics and isotherms. The results indicate that the PVA/PAA-hBN@PDA adsorbent has maximum adsorption capacities of 1029.57 mg/g, 793.65 mg/g, and 62.46 mg/g for methylene blue, crystal violet, and cobalt (II) ions, respectively. This underscores the superior performance of the PVA/PAA-hBN@PDA adsorbent when compared to both the PVA/PAA and PVA/PAA-hBN adsorbents. The adsorption kinetics adhered to a pseudo-second-order model, indicating chemisorption, whereas the Langmuir model implied a monolayer adsorption. Overall, the findings of this study highlight the efficacy of harnessing the synergistic capabilities of hBN and PDA within the PVA/PAA-hBN@PDA adsorbents, providing an efficient and eco-friendly approach to removing cationic dyes and heavy metals from contaminated water, and thereby contributing to a cleaner and safer environment for all.

Highly Conductive and Stable Composite Polymer Electrolyte with Boron Nitride Nanotubes for All-Solid-State Lithium Metal Batteries.

All-solid-state lithium metal batteries (ASSLMBs) have emerged as the most promising next-generation energy storage devices. However, the unsatisfactory ionic conductivity of solid electrolytes at room temperature has impeded the advancement of solid-state batteries. In this work, a multifunctional composite solid electrolyte (CSE) is developed by incorporating boron nitride nanotubes (BNNTs) into polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP). BNNTs, with a high aspect ratio, trigger the dissociation of Li salts, thus generating a greater population of mobile Li+, and establishing long-distance Li+ transport pathways. PVDF-HFP/BNNT exhibits a high ionic conductivity of 8.0 × 10-4 S cm-1 at room temperature and a Li+ transference number of 0.60. Moreover, a Li//Li symmetric cell based on PVDF-HFP/BNNT demonstrates robust cyclic performance for 3400 h at a current density of 0.2 mA cm-2. The ASSLMB formed from the assembly of PVDF-HFP/BNNT with LiFePO4 and Li exhibits a capacity retention of 93.2% after 850 cycles at 0.5C and 25 °C. The high-voltage all-solid-state LiCoO2/Li cell based on PVDF-HFP/BNNT also exhibits excellent cyclic performance, maintaining a capacity retention of 96.4% after 400 cycles at 1C and 25 °C. Furthermore, the introduction of BNNTs is shown to enhance the thermal conductivity and flame retardancy of the CSE.

Performance and Antiwear Mechanism of 1D and 2D Nanoparticles as Additives in a Polyalphaolefin.

This work is focused on the thermophysical and tribological study of eight nanolubricant compositions based on a polyalphaolefin (PAO 20) and two different nanoadditives: multi-walled carbon nanotubes (MWCNTs) and hexagonal boron nitride (h-BN). Regarding the thermophysical properties, density and dynamic viscosity of the base oil and the nanolubricants were measured in the range of 278.15-373.15 K, as well as their viscosity index, with the aim of evaluating the variation of these properties with the addition of the nanoadditives. On the other hand, their lubricant properties, such as contact angle, coefficient of friction, and wear surface, were determined to analyze the influence of the nanoadditives on the tribological performance of the base oil. The results showed that MWCNTs and h-BN nanoadditives improved the wear area by 29% and 37%, respectively, at a 0.05 wt% concentration. The density and dynamic viscosity increased compared with the base oil as the nanoadditive concentration increased. The addition of MWCNTs and h-BN nanoparticles enhanced the tribological properties of PAO 20 base oil.

Tunable Exciton Polaritons in Band-Gap Engineered Hexagonal Boron Nitride.

We show that hexagonal boron nitride (hBN), a two-dimensional insulator, when subjected to an external superlattice potential forms a paradigm for electrostatically tunable excitons in the near- and mid-ultraviolet (UV). With a combination of analytical and numerical methods, we see that the imposed potential has three consequences: (i) It renormalizes the effective mass tensor, leading to anisotropic effective masses. (ii) It renormalizes the band gap, eventually reducing it. (iii) It reduces the exciton binding energies. All these consequences depend on a single dimensionless parameter, which includes the product of strength of the external potential with its period. In addition to the excitonic energy levels, we compute the optical conductivity along two orthogonal directions and from it the absorption spectrum. The results for the latter show that our system is able to mimic a grid polarizer. These characteristics make one-dimensional hBN superlattices a viable and meaningful platform for fine-tuned polaritonics in the UV to visible spectral range.

Modification Strategies of Hexagonal Boron Nitride Nanomaterials for Photocatalysis.

Although hexagonal boron nitride (h-BN) was initially considered a less promising photocatalyst due to its large band gap and apparent chemical inertness, its unique two-dimensional lamellar structure coupled with high stability and environmental friendliness, as the second largest van der Waals material after graphene, provides a unique platform for photocatalytic innovation. This review not only highlights the intrinsic qualities of h-BN with photocatalytic potentials, such as high stability, environmental compatibility, and tunable bandgap through various modification strategies but also provides a comprehensive overview of the recent advances in h-BN-based nanomaterials for environmental and energy applications, as well as an in-depth description of the modification methods and fundamental properties for these applications. In addition, we discuss the challenges and prospects of h-BN-based nanomaterials for future photocatalysis.

Enhanced Long-Term Stability of Crystalline Nickel-Boride (Ni23B6) Electrocatalyst by Encapsulation with Hexagonal Boron Nitride.

Nickel boride catalysts show great potential as low-cost and efficient alternatives to noble-metal catalysts in acidic media; however, synthesizing and isolating a specific phase and composition of nickel boride is nontrivial, and issues persist in their long-term stability as electrocatalysts. Here, a single-crystal nickel boride, Ni23B6, is reported which exhibits high electrocatalytic activity for the hydrogen evolution reaction (HER) in an acidic solution, and that its poor long-term stability can be overcome via encapsulation by single-crystal trilayer hexagonal boron nitride (hBN) film. Interestingly, hBN-covered Ni23B6 on a Ni substrate shows an identical overpotential of 52 mV at a current density of 10 mA cm-2 to that of bare Ni23B6. This phenomenon indicates that the single-crystalline hBN layer is catalytically transparent and does not obstruct HER activation. The hBN/Ni23B6/Ni has remarkable long-term stability with negligible changes to its polarization curves for 2000 cycles, whereas the Ni23B6/Ni shows significant degradation after 650 cycles. Furthermore, chronoamperometric measurements indicate that stability is preserved for >20 h. Long-term stability tests also reveal that the surface morphology and chemical structure of the hBN/Ni23B6/Ni electrode remain preserved. This work provides a model for the practical design of robust and durable electrochemical catalysts through the use of hBN encapsulation.

Unraveling the Impact of Boron Nitride and Silicon Nitride Nanoparticles on Thermoplastic Polyurethane Fibers and Mats for Advanced Heat Management.

The urgent challenges posed by the energy crisis, alongside the heat dissipation of advanced electronics, have embarked on a rising demand for the development of highly thermally conductive polymer composites. Electrospun composite mats, known for their flexibility, permeability, high concentration and orientational degree of conductive fillers, stand out as one of the prime candidates for addressing this need. This study explores the efficacy of boron nitride (BN) and its potential alternative, silicon nitride (SiN) nanoparticles, in enhancing the thermal performance of the electrospun composite thermoplastic polyurethane (TPU) fibers and mats. The 3D reconstructed models obtained from FIB-SEM imaging provided valuable insights into the morphology of the composite fibers, aiding the interpretation of the measured thermal performance through scanning thermal microscopy for the individual composite fibers and infrared thermography for the composite mats. Notably, we found that TPU-SiN fibers exhibit superior heat conduction compared to TPU-BN fibers, with up to a 6 °C higher surface temperature observed in mats coated on copper pipes. Our results underscore the crucial role of arrangement of nanoparticles and fiber morphology in improving heat conduction in the electrospun composites. Moreover, SiN nanoparticles are introduced as a more suitable filler for heat conduction enhancement of electrospun TPU fibers and mats, suggesting immense potential for smart textiles and thermal management applications.

Recent advances in two-dimensional perovskite materials for light-emitting diodes.

Light-emitting diodes (LEDs) are an indispensable part of our daily life. After being studied for a few decades, this field still has some room for improvement. In this regard, perovskite materials may take the leading role. In recent years, LEDs have become a most explored topic, owing to their various applications in photodetectors, solar cells, lasers, and so on. Noticeably, they exhibit significant characteristics in developing LEDs. The luminous efficiency of LEDs can be significantly enhanced by the combination of a poor illumination LED with low-dimensional perovskite. In 2014, the first perovskite-based LED was illuminated at room temperature. Furthermore, two-dimensional (2D) perovskites have enriched this field because of their optical and electronic properties and comparatively high stability in ambient conditions. Recent and relevant advancements in LEDs using low-dimensional perovskites including zero-dimensional to three-dimensional materials is reported. The major focus of this article is based on the 2D perovskites and their heterostructures (i.e., a combination of 2D perovskites with transition metal dichalcogenides, graphene, and hexagonal boron nitride). In comparison to 2D perovskites, heterostructures exhibit more potential for application in LEDs. State-of-the-art perovskite-based LEDs, current challenges, and prospects are also discussed.

Probing Defectivity Beneath the Hydrocarbon Blanket in 2D hBN Using TEM-EELS.

The controlled creation and manipulation of defects in 2D materials has become increasingly popular as a means to design and tune new material functionalities. However, defect characterization by direct atomic-scale imaging is often severely limited by surface contamination due to a blanket of hydrocarbons. Thus, analysis techniques that can characterize atomic-scale defects despite the contamination layer are advantageous. In this work, we take inspiration from X-ray absorption spectroscopy and use broad-beam electron energy loss spectroscopy (EELS) to characterize defect structures in 2D hexagonal boron nitride (hBN) based on averaged fine structure in the boron K-edge. Since EELS is performed in a transmission electron microscope (TEM), imaging can be performed in-situ to assess contamination levels and other factors such as tears in the fragile 2D sheets, which can affect the spectroscopic analysis. We demonstrate the TEM-EELS technique for 2D hBN samples irradiated with different ion types and doses, finding spectral signatures indicative of boron-oxygen bonding that can be used as a measure of sample defectiveness depending on the ion beam treatment. We propose that even in cases where surface contamination has been mitigated, the averaging-based TEM-EELS technique can be useful for efficient sample surveys to support atomically resolved EELS experiments.

Attojoule Hexagonal Boron Nitride-Based Memristor for High-Performance Neuromorphic Computing.

In next-generation neuromorphic computing applications, the primary challenge lies in achieving energy-efficient and reliable memristors while minimizing their energy consumption to a level comparable to that of biological synapses. In this work, hexagonal boron nitride (h-BN)-based metal-insulator-semiconductor (MIS) memristors operating is presented at the attojoule-level tailored for high-performance artificial neural networks. The memristors benefit from a wafer-scale uniform h-BN resistive switching medium grown directly on a highly doped Si wafer using metal-organic chemical vapor deposition (MOCVD), resulting in outstanding reliability and low variability. Notably, the h-BN-based memristors exhibit exceptionally low energy consumption of attojoule levels, coupled with fast switching speed. The switching mechanisms are systematically substantiated by electrical and nano-structural analysis, confirming that the h-BN layer facilitates the resistive switching with extremely low high resistance states (HRS) and the native SiOx on Si contributes to suppressing excessive current, enabling attojoule-level energy consumption. Furthermore, the formation of atomic-scale conductive filaments leads to remarkably fast response times within the nanosecond range, and allows for the attainment of multi-resistance states, making these memristors well-suited for next-generation neuromorphic applications. The h-BN-based MIS memristors hold the potential to revolutionize energy consumption limitations in neuromorphic devices, bridging the gap between artificial and biological synapses.

Large-Scale Statistical Analysis of Defect Emission in hBN: Revealing Spectral Families and Influence of Flake Morphology.

Quantum emitters in two-dimensional layered hexagonal boron nitride are quickly emerging as a highly promising platform for next-generation quantum technologies. However, the precise identification and control of defects are key parameters to achieve the next step in their development. We conducted a comprehensive study by analyzing over 10,000 photoluminescence emission lines from liquid exfoliated hBN nanoflake samples, revealing 11 narrow sets of defect families within the 1.6 to 2.2 eV energy range. This challenges hypotheses of a random energy distribution. We also reported averaged defect parameters, including emission line widths, spatial density, phonon side bands, and Franck-Condon-related factors. These findings provide valuable insights into deciphering the microscopic origin of emitters in hBN hosts. We also explored the influence of the hBN host morphology on defect family formation, demonstrating its crucial impact. By tuning the flake size and arrangement, we achieve selective control of defect types while maintaining high spatial density. This offers a scalable approach to defect emission control, diverging from costly engineering methods. It emphasizes the significance of the morphological aspects of hBN hosts for gaining insights into defect origins and expanding their spectral control.

Conductive/Insulating Bioinks with Multitechnology Compatibility and Adjustable Performance.

Conducting/insulating inks have received significant attention for the fabrication of a wide range of additive manufacturing technology. However, current inks often demonstrate poor biocompatibility and face trade-offs between conductivity and mechanical stiffness under physiological conditions. Here, conductive/insulating bioinks based on two-dimensional materials are proposed. The conductive bioink, graphene (GR)-poly(lactic-co-glycolic acid) (PLGA), is prepared by introducing conductive GR into a degradable polymer matrix, PLGA, while the insulating bioink, boron nitride (BN)-PLGA, is synthesized by adding insulating BN. By optimizing the material ratios, this work achieves precise control of the electromechanical properties of the bioinks, thereby enabling the flexible construction of conductive networks according to specific requirements. Furthermore, these bioinks are compatible with a variety of manufacturing technologies such as 3D printing, electrospinning, spin coating, and injection molding, expanding their application range in the biomedical field. Overall, the results suggest that these conducting/insulating bioinks offer improved mechanical, electronic, and biological properties for various emerging biomedical applications.

Stretching Aligned Hydrogen Bonding Network to Evoke Mechanically Robust and High-Energy-Density P(VDF-HFP) Dielectric Film Capacitors.

Polymer-based dielectric film capacitors are essential energy storage components in electronic and power systems due to their ultrahigh power density and ultra-fast charge storage/release capability. Nonetheless, their relatively low energy density does not fully meet the requirements of power electronics and pulsed power systems. Herein, a scalable composite dielectric film based on a ferroelectric polymer with edge hydroxylated boron nitride nanosheets (BNNS-OH) is fabricated via the construction of a hydrogen bonding network and stretching orientation strategy. The presence of hydroxyl groups on boron nitride aids in forming a robust hydrogen bonding network within the ferroelectric polymer, leading to a significant increase in Young's modulus and superior dielectric performance. Furthermore, the stretching process aligns the BNNS-OH and the hydrogen bonding network along the drawing direction via covalent and hydrogen bonding interaction, resulting in a remarkable tensile strength (109 MPa), breakdown strength (688 MV m-1), and energy density (28.2 J cm-3), outperforming mostrepresentative polymer-based dielectric films. In combining the advantages of a simple preparation process, extraordinary energy storage performance, and low-cost raw materials, this strategy is viable for large-scale production of polymer-based dielectric films with high mechanical and dielectric performance and opens a new path for the development of next-generation energy storage applications.

DIW-Printed Thermal Management PDMS Composites with 3D Structural Thermal Conductive Network of h-BN Platelets and Al2O3 Nanoparticles.

Electronic devices play an increasingly vital role in modern society, and heat accumulation is a major concern during device development, which causes strong market demand for thermal conductivity materials and components. In this paper, a novel thermal conductive material consisting of polydimethylsiloxane (PDMS) and a binary filler system of h-BN platelets and Al2O3 nanoparticles was successfully fabricated using direct ink writing (DIW) 3D printing technology. The addictive manufacturing process not only endows the DIW-printed composites with various geometries but also promotes the construction of a 3D structural thermal conductive network through the shearing force during the printing process. Moreover, the integrity of the thermal conductive network can be optimized by filling the gaps between the BN platelets with Al2O3 particles. Resultingly, the configuration of the binary fillers is arranged by the shearing force during the DIW process, fabricating the thermal conductive network of oriented fillers. The DIW-printed BN/Al2O3/PDMS with 45 wt% thermal conductive binary filler can reach a thermal conductivity of 0.98 W/(m·K), higher than the 0.62 W/(m·K) of the control sample. In this study, a novel strategy for the thermal conductive performance improvement of composites based on DIW technology is successfully verified, paving a new way for thermal management.

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

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

Synthesis of Few-Layer Hexagonal Boron Nitride for Magnetic Tunnel Junction Application.

Hexagonal boron nitride (hBN), a wide-gap two-dimensional (2D) insulator, is an ideal tunneling barrier for many applications because of the atomically flat surface, high crystalline quality, and high stability. Few-layer hBN with a thickness of 1-2 nm is an effective barrier for electron tunneling, but the preparation of few-layer hBN relies on mechanical exfoliation from bulk hBN crystals. Here, we report the large-area growth of few-layer hBN by chemical vapor deposition on ferromagnetic Ni-Fe thin films and its application to tunnel barriers of magnetic tunnel junction (MTJ) devices. Few-layer hBN sheets mainly consisting of two to three layers have been successfully synthesized on a Ni-Fe catalyst at a high growth temperature of 1200 °C. The MTJ devices were fabricated on as-grown hBN by using the Ni-Fe film as the bottom ferromagnetic electrode to avoid contamination and surface oxidation. We found that trilayer hBN gives a higher tunneling magnetoresistance (TMR) ratio than bilayer hBN, resulting in a high TMR ratio up to 10% at ∼10 K.

2D Materials-Based Thermal Interface Materials: Structure, Properties, and Applications.

The challenges associated with heat dissipation in high-power electronic devices used in communication, new energy, and aerospace equipment have spurred an urgent need for high-performance thermal interface materials (TIMs) to establish efficient heat transfer pathways from the heater (chip) to heat sinks. Recently, emerging 2D materials, such as graphene and boron nitride, renowned for their ultrahigh basal-plane thermal conductivity and the capacity to facilitate cross-scale, multi-morphic structural design, have found widespread use as thermal fillers in the production of high-performance TIMs. To deepen the understanding of 2D material-based TIMs, this review focuses primarily on graphene and boron nitride-based TIMs, exploring their structures, properties, and applications. Building on this foundation, the developmental history of these TIMs is emphasized and a detailed analysis of critical challenges and potential solutions is provided. Additionally, the preparation and application of some other novel 2D materials-based TIMs are briefly introduced, aiming to offer constructive guidance for the future development of high-performance TIMs.