Two-dimensional Boron Nitride Research Articles

Transferrable AlGaN/GaN High-Electron Mobility Transistors to Arbitrary Substrates via a Two-Dimensional Boron Nitride Release Layer.

Mechanical transfer of high-performing thin-film devices onto arbitrary substrates represents an exciting opportunity to improve device performance, explore nontraditional manufacturing approaches, and paves the way for soft, conformal, and flexible electronics. Using a two-dimensional boron nitride release layer, we demonstrate the transfer of AlGaN/GaN high-electron mobility transistors (HEMTs) to arbitrary substrates through both direct van der Waals bonding and with a polymer adhesive interlayer. No device degradation was observed because of the transfer process, and a significant reduction in device temperature (327-132 °C at 600 mW) was observed when directly bonded to a silicon carbide (SiC) wafer relative to the starting wafer. With the use of a benzocyclobutene (BCB) adhesion interlayer, devices were easily transferred and characterized on Kapton and ceramic films, representing an exciting opportunity for integration onto arbitrary substrates. Upon reduction of this polymer adhesive layer thickness, the AlGaN/GaN HEMTs transferred onto a BCB/SiC substrate resulted in comparable peak temperatures during operation at powers as high as 600 mW to the as-grown wafer, revealing that by optimizing interlayer characteristics such as thickness and thermal conductivity, transferrable devices on polymer layers can still improve performance outputs.

Seeing Dirac electrons and heavy fermions in new boron nitride monolayers**Project supported by the National Natural Science Foundation of China (Grant No. 11874314) and the Natural Science Foundation of Hunan Province, China (Grant No. 2018JJ2377).

Most three-dimensional (3D) and two-dimensional (2D) boron nitride (BN) structures are wide-band-gap insulators. Here, we propose two BN monolayers having Dirac points and flat bands, respectively. One monolayer is named as 5–7 BN that consists of five- and seven-membered rings. The other is a Kagome BN made of triangular boron rings and nitrogen dimers. The two structures show not only good dynamic and thermodynamic stabilities but also novel electronic properties. The 5–7 BN has Dirac points on the Fermi level, indicating that the structure is a typical Dirac material. The Kagome BN has double flat bands just below the Fermi level, and thus there are heavy fermions in the structure. The flat-band-induced ferromagnetism is also revealed. We analyze the origination of the band structures by partial density of states and projection of orbitals. In addition, a possible route to experimentally grow the two structures on some suitable substrates such as the PbO2 (111) surface and the CdO (111) surface is also discussed, respectively. Our research not only extends understanding on the electronic properties of BN structures, but also may expand the applications of BN materials in 2D electronic devices.

Effect of 2-D BN on enhanced corona-resistant characteristic of PI/AlN+BN composite investigated by quasi-in-situ technology

Incorporating two-dimensional (2-D) boron nitride (BN) into polyimide/aluminum nitride (PI/AlN) renders a simple strategy in producing new ternary composite films with longer corona aging life and higher breakdown strength compared with PI/AlN. During corona aging process, the effects of 2-D BN on adjusting the microstructure evolution of ternary composites were investigated using quasi-in-situ technology systematically as follow: (SEM), (AFM), (FTIR), (XRD) and (SAXS) at different corona time. Quasi-in-situ characterization results show that the corona aging modes of the two composite films are quite different, the introduction of BN nanosheets could protect the C–N–C and C–O–C bonds from breaking as well as accelerate the fillers expose via autoxidation reaction. In addition, BN nanosheets could induce the distance between PI molecular chains to shorten during the corona process, resulting in more dense structures coordinating with AlN and PI. Different corona aging mechanism compared with that of the PI/AlN composite films was proposed. This work demonstrated the effect of 2-D BN nanosheets in the PI/AlN+BN ternary composites, which can be used to expand their application in insulating polymer based composites.

Insights into water permeability and Hg2+ removal using two-dimensional nanoporous boron nitride

Industrial wastewater containing Hg2+, when discharged into nature, will pose a serious threat to ecological security.

Synthesis, Functionalization, and Bioapplications of Two-Dimensional Boron Nitride Nanomaterials.

Two-dimensional boron nitride nanostructures (2D-BNNs) have been increasingly investigated for their applications in several scientific and technological areas. This considerable interest is due to their unique physicochemical properties, which include high hydrophobicity, heat and electrical insulation, resistance to oxidation, antioxidation capacity, thermal conductivity, high chemical stability, mechanical strength, and hydrogen storage capacity. They are also used as fillers, antibacterial agents, protective coating agents, lubricants, boron neutron capture therapy agents, nanocarriers for drug delivery, and for the receptor phase in chemosensors. The investigations for their use in medicine and biomedicine are very promising, including cancer therapy and wound healing. In this review, 2D-BNNs synthesis and their surface modification strategies, biocompatibility, and bioapplication studies are discussed. Finally, a perspective for the future use of these novel nanomaterials in the biomedical field is provided.

Highly Adhesive Li-BN Nanosheet Composite Anode with Excellent Interfacial Compatibility for Solid-State Li Metal Batteries.

Solid-state lithium metal batteries (SSLMBs) are promising energy storage devices by employing lithium metal anodes and solid-state electrolytes (SSEs) to offer high energy density and high safety. However, their efficiency is limited by Li metal/SSE interface barriers, including insufficient contact area and chemical/electrochemical incompatibility. Herein, a strategy to effectively improve the adhesiveness of Li metal to garnet-type SSE is proposed by adding only a few two-dimensional boron nitride nanosheets (BNNS) (5 wt %) into Li metal by triggering the transition from point contact to complete adhesion between Li metal and ceramic SSE. The interface between the Li-BNNS composite anode and the garnet exhibits a low interfacial resistance of 9 Ω cm2, which is significantly lower than that of bare Li/garnet interface (560 Ω cm2). Furthermore, the enhanced contact and the additional BNNS in the interface act synergistically to offer a high critical current density of 1.5 mA/cm2 and a stable electrochemical plating/striping over 380 h. Moreover, the full cell paired with the Li-BNNS composite anode and the LiFePO4 cathode shows stable cycling performance at room temperature. Our results introduce an appealing composite strategy with two-dimensional materials to overcome the interface challenges, which provide more opportunities for the development of SSLMBs.

Deep-ultraviolet integrated photonic and optoelectronic devices: A prospect of the hybridization of group III–nitrides, III–oxides, and two-dimensional materials

Progress in the design and fabrication of ultraviolet and deep-ultraviolet group III–nitride optoelectronic devices, based on aluminum gallium nitride and boron nitride and their alloys, and the heterogeneous integration with two-dimensional and oxide-based materials is reviewed. We emphasize wide-bandgap nitride compound semiconductors (i.e., (B, Al, Ga)N) as the deep-ultraviolet materials of interest, and two-dimensional materials, namely graphene, two-dimensional boron nitride, and two-dimensional transition metal dichalcogenides, along with gallium oxide, as the hybrid integrated materials. We examine their crystallographic properties and elaborate on the challenges that hinder the realization of efficient and reliable ultraviolet and deep-ultraviolet devices. In this article we provide an overview of aluminum nitride, sapphire, and gallium oxide as platforms for deep-ultraviolet optoelectronic devices, in which we criticize the status of sapphire as a platform for efficient deep-ultraviolet devices and detail advancements in device growth and fabrication on aluminum nitride and gallium oxide substrates. A critical review of the current status of deep-ultraviolet light emission and detection materials and devices is provided.

Polyvinylidene fluoride phase design by two-dimensional boron nitride enables enhanced performance and stability for seawater desalination

The instability of polyvinylidene fluoride (PVDF) membranes in membrane distillation (MD) for seawater desalination is still a problem, despite the tremendous effort expended to resolve this issue. Here, a simple and feasible approach for improving desalination performance through the incorporation of two-dimensional boron nitride nanosheets (BNNSs) in polyvinylidene fluoride-co-hexafluoropropene (PVDF-co-HFP) electrospun nanofiber membrane (BNs-PH) is proposed as well as demonstrate its origin for fundamental understanding. The BNs-PH membrane exhibits a stable water vapor flux (18 LMH) and superior salt rejection (99.99%), even after operation for 280 h (commercial PVDF: steep decay within 28 h; neat PH: wetting within 4 h). From structural/chemical analyses, the BNNSs play a crucial role in forming favorable phases of the PH polymer crystal structure, inducing a superhydrophobic surface with greater nanoporosity and higher heterogeneity as well as enhanced mechanical properties (increase of UTS: 13.4%; modulus: 1.2%) for long-term operation. Theoretical modeling results of an air-gap MD system are consistent with our experimental results. The approach introduced in this study can be applied to other desalination systems to boost various water treatment applications.

Synthesis of Sandwich-Like Nanostructure Fillers and Their Use in Different Types of Thermal Composites.

Thermally conductive yet electrically insulating two-dimensional boron nitride nanosheets (BNNSs) have been an ideal choice for the enhanced fillers for improving thermal properties of polymer-based composites. As a nanofiller with an ultrahigh aspect ratio, BNNSs result in conspicuous stacking along the planar direction in the preparation of composites, which results in strong anisotropy of heat transfer and suppresses out-plane thermal dissipation. Thus, it is necessary to facilitate the out-plane heat transfer by building a favorable microstructure. Focusing on the structural design of the nanofiller itself here, we have fabricated a novel three-dimensional nanofiller with improved out-plane connections. Carbon nanotubes (CNTs) have been grown in situ on the surface of BNNSs using chemical vapor deposition. Utilizing these sandwich-like nanostructure BNNSs/CNTs as fillers in the composites, we have assembled diverse sorts of composites, such as flexible films, scleroid 3D mats, painted ink, and viscous grease. Simultaneously, their thermal and insulating properties have been evaluated. A nearly 330% enhancement of out-plane thermal conductivity from the control sample filled with pristine BNNS is achieved, and the composite also exhibits good electrical resistivity of above 7.5 × 1010 Ω mm. The results indicate that the BNNS/CNT filler has superior thermal performance over the original BNNS while maintaining a satisfactory electrical resistivity to avoid short-circuits in high-power electronics. Furthermore, the prepared grease used as a thermal interface material shows impressive heat dissipation performance when applied on a running computer.

Piezoelectric Energy Harvesting from Two-Dimensional Boron Nitride Nanoflakes.

Two-dimensional (2D) piezoelectric hexagonal boron nitride nanoflakes (h-BN NFs) were synthesized by a mechanochemical exfoliation process and transferred onto an electrode line-patterned plastic substrate to characterize the energy harvesting ability of individual NFs by external stress. A single BN NF produced alternate piezoelectric output sources of ∼50 mV and ∼30 pA when deformed by mechanical bendings. The piezoelectric voltage coefficient (g11) of a single BN NF was experimentally determined to be 2.35 × 10-3 V·m·N-1. The piezoelectric composite composed of BN NFs and an elastomer was spin-coated onto a bulk Si substrate and then transferred onto the electrode-coated plastic substrates to fabricate a BN NFs-based flexible piezoelectric energy harvester (f-PEH) which converted a piezoelectric voltage of ∼9 V, a current of ∼200 nA, and an effective output power of ∼0.3 μW. This result provides a new strategy for precisely characterizing the energy generation ability of piezoelectric nanostructures and for demonstrating f-PEH based on 2D piezomaterials.

Two-dimensional boron nitride as a sulfur fixer for high performance rechargeable aluminum-sulfur batteries

Aluminum-ion batteries (AIBs) are regarded as promising candidates for post-lithium-ion batteries due to their lack of flammability and electrochemical performance comparable to other metal-ion batteries. The lack of suitable cathode materials, however, has hindered the development of high-performing AIBs. Sulfur is a cost-efficient material, having distinguished electrochemical properties, and is considered an attractive cathode material for AIBs. Several pioneering reports have shown that aluminum-sulfur batteries (ASBs) exhibit superior electrochemical capacity over other cathode materials for AIBs. However, a rapid decay in the capacity is a huge barrier for their practical applications. Here, we have demonstrated systematically for the first time that the two-dimensional layered materials (e.g. MoS2, WS2, and BN) can serve as fixers of S and sulfide compounds during repeated charge/discharge processes; BN/S/C displays the highest capacity of 532 mAh g−1 (at a current density of 100 mA g−1) compared with the current state-of-the-art cathode material for AIBs. Further, we could improve the life-span of ASBs to an unprecedented 300 cycles with a high Coulombic efficiency of 94.3%; discharge plateaus at ~1.15 V vs. AlCl4−/Al was clearly observed during repeated charge/discharge cycling. We believe that this work opens up a new method for achieving high-performing ASBs.

The two-dimensional boron nitride hierarchical nanostructures: Controllable synthesis and superhydrophobicity

Layered boron nitride materials are used as superb protective coatings and reinforcing materials due to their high mechanical strength and chemical inertness. Herein, we report on the synthesis of two dimensional boron nitride (2D-BN) hierarchical nanostructures by a facile and efficient approach using boric acid (H3BO3) and hexamethylenetetramine (C6H12N4) as a reaction precursors. Our findings indicate that 2D hierarchical nanostructure was an assembling of BN quantum dots and exhibit varied wetting properties. The shape, size, and thickness of the BN quantum dots were well controlled by properly adjusting the growth parameters. With changing the temperature and other reaction conditions as well as ratios of reactants, the average size of BN quantum dots varies from 35 nm to 5 nm. Strong superhydrophobic properties with the contact angle of 155° are obtained for 2D-BN. These 2D-BN nanostructure possesses the properties conflicting to carbon nanomaterials such as high temperature stability, high chemical inertness and intrinsically semiconducting and may find application in nanoelectronics, catalyst support, as a composite materials and self-cleaning coatings etc., especially those working in harsh environment and at high temperature.

Low temperature functionalization of two-dimensional boron nitride for electrochemical sensing

Two-dimensional hexagonal boron nitride (h-BN) as an emerging nanomaterial exhibits unique physicochemical properties, making it suitable candidate for a wide spectrum of applications. However, due to its poor functionality, the processability of this nanomaterial is low. In this work, we report on a straightforward and scalable approach for the functionalization of h-BN by nitrene [2 + 1] cycloaddition at room temperature. The triazine-functionalized h-BN (Trz-BNs) showed a high reactivity toward nucleophiles, through which post-modifications are performable. The post-modification of Trz-BNs by L-cysteine was studied using cyclic voltammetry and differential pulse voltammetry. Taking advantage of the scalable and straightforward functionalization as well as ability of triazine functional groups for the controlled post-modifications, Trz-BNs is a promising nanoplatform for a wide range of future applications.

Enhanced catalytic degradation of bisphenol A by hemin-MOFs supported on boron nitride via the photo-assisted heterogeneous activation of persulfate

The wide variety applications of Bisphenol A (BPA) have resulted in the world wide concerns because of its toxicity and estrogenic activity. Thus, it is critical to explore efficient method for the degradation of BPA. In this study, biomimetic metal-organic-frameworks (MOFs), composed of hemin as the organic linkage and copper ions as the nodes, supported on two-dimensional boron nitride (BN) have been fabricated via facile one-pot hydrothermal approach. The multifunctional Cu-hemin-MOFs/BN composites were applied to activate persulfate (PS) for the degradation of bisphenol A (BPA). Results showed that over 99% of BPA (40 mg/L) was degraded in 30 min under visible-light irradiation with a fast degradation kinetic (0.10 min−1). As compared with the traditional homogeneous catalysts, these Cu-hemin-MOFs based heterogeneous catalysts hold the advantages of high efficiency, easily separation, recycle and reuse without introducing secondary pollution. The BN not only acted as stabilizer to support the hemin-MOFs but also worked as adsorbents for the pre-concentration of the pollutants. Meanwhile, Cu-hemin-MOFs with dual active sites of the Fe and Cu were responsible for the PS activation, leading to the efficient degradation of BPA. Electron spin resonance (ESR) and radicals quenching experiments revealed the SO4– and OH were the main active radicals for the BPA oxidation. These findings indicated the synergistically combination of the hemin-MOFs with the 2D BN nanoplates endowed the composites with multifunctional properties, leading to the excellent catalytic activity for the oxidation of pollutants. This study provides new insights into the design and fabrication of novel MOF-based heterogeneous catalysts for the application in environmental remediation.

Thermal Characterization of Low-Dimensional Materials by Resistance Thermometers.

The design, fabrication, and use of a hotspot-producing and temperature-sensing resistance thermometer for evaluating the thermal properties of low-dimensional materials are described in this paper. The materials that are characterized include one-dimensional (1D) carbon nanotubes, and two-dimensional (2D) graphene and boron nitride films. The excellent thermal performance of these materials shows great potential for cooling electronic devices and systems such as in three-dimensional (3D) integrated chip-stacks, power amplifiers, and light-emitting diodes. The thermometers are designed to be serpentine-shaped platinum resistors serving both as hotspots and temperature sensors. By using these thermometers, the thermal performance of the abovementioned emerging low-dimensional materials was evaluated with high accuracy.

Chemically exfoliated boron nitride nanosheets form robust interfacial layers for stable solid-state Li metal batteries.

Two-dimensional (2D) boron nitride nanosheets (BNNSs) were chemically exfoliated from bulk boron nitride and coated onto the surface of a poly(ethylene oxide) (PEO)-based electrolyte through a dry-pressing transfer process. The fabricated BNNSs coating formed a robust interfacial layer to improve the chemical and mechanical stability of the PEO-based electrolyte, leading to the enhanced performance of solid-state Li metal batteries.

Preparation of two-dimensional magnetic molecularly imprinted polymers based on boron nitride and a deep eutectic solvent for the selective recognition of flavonoids

New types of two-dimensional (2D) boron nitride (BN) were developed as a 2D scaffold material. After modification with ternary deep eutectic solvents (DES, ChCl-caffeic acid-ethylene glycol), the processed BN was applied to the preparation of magnetic molecularly imprinted polymers (MMIPs). In the polymerization of MMIPs, DESs and hydrophobic Fe3O4 magnetite were applied as the functional monomer and magnetically susceptible component, respectively. A 2D ellipsoid material was formed successfully by polymerization on the surface of the processed BN. The proposed 2D-MMIPs were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and nitrogen sorption analysis techniques. The surface area of the 2D-MMIPs was increased using eco-friendly chemicals. The proposed 2D-MMIPs had a 2D oblate structure and a large surface area. The 2D-MMIPs were used for the preconcentration of flavonoids from Ginkgo biloba leaf extracts. High performance liquid chromatography-ultraviolet analysis revealed that the 2D-MMIPs have higher recoveries for the flavonoids (quercetin 96.8%, isorhamnetin 93.6% and kaempferol 94.8%) in Ginkgo biloba leaves than common MMIPs.

A single-atom catalyst of cobalt supported on a defective two-dimensional boron nitride material as a promising electrocatalyst for the oxygen reduction reaction: a DFT study.

Single-atom catalysts present extraordinary catalytic performance towards various reactions. In this work, the possibility of single Co atoms supported by the experimentally available defective two-dimensional boron nitride material (2D-BN) with boron vacancies (Co/BN) as a potential catalyst for the oxygen reduction reaction (ORR) was investigated by density functional theory. Co/BN has a similar active center to the cobalt nitride species, which have been proved to be effective ORR catalysts. It is found that Co atoms bind with the defective 2D-BN strongly to ensure the stability of Co/BN. Moreover, all of the ORR intermediates can be adsorbed on Co/BN. Especially, the HOOH species is found to be unstable and decomposes into two OH species immediately, suggesting that the ORR process occurs on Co/BN only through a direct 4e- pathway. Along the favorable pathway, the reduction of O2 to OOH is the rate-limiting step with a largest activation barrier of 0.30 eV and the maximum free energy change is 0.82 eV. Co/BN exhibits competitive ORR activity with that of CoN3 embedded graphene and Pt-based catalysts. These results should be enlightening to understand the ORR mechanism on Co/BN and design novel single-atom catalysts for the ORR and other electrocatalysis reactions.

Theoretical analysis of oxygen reduction reaction activity on single metal (Ni, Pd, Pt, Cu, Ag, Au) atom supported on defective two-dimensional boron nitride materials.

A single atom supported by two-dimensional material is a suitable candidate for an oxygen reduction reaction (ORR) to replace Pt-based catalysts. In this work, new promising single-atom catalysts (SACs) with precise metal-nitrogen coordination (M-N) were investigated, where a single transition metal atom (M = Ni, Pd, Pt, Cu, Ag, Au) was supported by experimentally available defective two-dimensional boron nitride materials (M/BN) with a boron vacancy. ORR performance is predicated by the volcano plot, which indicates that those M/BN catalysts offer optimized binding strength of *OH species exhibiting high ORR activity. Moreover, only a direct 4e- pathway occurs on Ni/BN, Pd/BN and Pt/BN with only d valence electrons of a single metal atom. As an example, Pd/BN catalyzes ORR via a direct 4e- pathway with a small reaction barrier of 0.42 eV, which is smaller than that of Pt-based catalysts (0.79 eV). This high activity is attributed to precise M-N3 coordination in the M/BN catalysts. This work is expected to provide useful insight for development of novel high-efficiency SACs for ORR.

Water transport properties of boron nitride nanosheets mixed matrix membranes for humic acid removal

Ultrafiltration grade polysulfone-based mixed matrix membranes (MMMs) incorporated with two-dimensional boron nitride nanosheet (BNNS) was prepared via phase inversion method. The amount of BN incorporated was varied and the influence on membrane morphology, contact angle, surface charge, as well as water permeability and humic acid rejection were investigated. Results revealed that the addition of BN to the membrane matrix resulted in profound increase in water permeability (almost tripled to that of neat PSf) and humic acid rejection due to the increase in pore size and surface negative charge. Beyond the morphological changes imparted by the inclusion of BNNS, we postulated that the presence of BNNS within the membrane matrix also contribute to the enhancement in flux and rejection based on surface-slip and selective interlayer transport. Despite the favourable augmentation of water transport and filtration performance, the MMMs suffered with fouling problem due to the entrapment of foulant within the enlarged pores and the membrane valleys. Its inherent adsorptive character could be a disadvantage when utilized as membrane filler.