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Synergic effect of pore size engineering and an applied electric field on the controlled permeation of alkali metal atoms and ions across pristine and defect-containing h-BN sheets
摘要： The permeation and selectivity of alkali metal atoms and ions through normal and defected hexagonal boron nitride was studied in the presence and absence of water and an electric field. The defects include one (VB & VN), two (VBN) and three atom (VN2B) vacancies. The morphology and size of the pore (defect) in the h-BN sheet significantly affect the energy barriers. These results indicate that an h-BN sheet with appropriate pore size possesses good Li/Li+ selectivity. The permeation of lithium atoms through VN2B-h-BN is almost a barrierless process (1.75 kcal mol?1). Moreover, the VBN h-BN nanosheet selectively allows the passage of Li atoms at room temperature with the highest selectivity ratio of 1.58 × 1013. The presence of water molecules increases the barrier of alkali metal atom permeation. The effect of water molecules is more pronounced for alkali metal atom permeation through a defected h-BN nanosheet as compared to alkali metal ions. An applied electric field perpendicular to the h-BN sheet further decreases the permeation barriers. For example, the energy barrier is reduced to 31 kcal mol?1 (from 34 kcal mol?1) in the presence of an electric field for the permeation of lithium through H2O–VB h-BN–H2O. These studies can be extended to investigate the separation capability of porous hexagonal boron nitride nanosheets for other metal atoms and ions.
关键词： electric field,permeation,water molecules,alkali metal atoms,hexagonal boron nitride,defects,ions,selectivity
更新于2025-09-23 15:21:01
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Dependence of h-BN film thickness as grown on nickel single crystal substrates of different orientation
摘要： Chemical vapor deposition of 2D materials has been an active area of research in recent years because it is a scalable process for obtaining thin films that can be used to fabricate devices. The growth mechanism for hexagonal boron nitride (h-BN) on metal catalyst substrates has been described to be either surface energy driven or diffusion driven. In this work, h-BN is grown in a CVD system on Ni single crystal substrates as a function of Ni crystallographic orientation to clarify the competing forces acting on the growth mechanism. We observed that the thickness of the h-BN film depends on the Ni substrate orientation, with the growth rate increasing from the (100) surface to the (111) surface, and the highest on the (110) surface. We associate the observed results with surface reactivity and diffusivity differences for different Ni orientations. Boron and nitrogen diffuse and precipitate from the Ni bulk to form thin multilayer h-BN. Our results serve to clarify the h-BN CVD growth mechanism which has been previously ascribed to a surface energy-driven growth mechanism.
关键词： surface diffusion,electron backscatter diffraction,growth mechanism,hexagonal boron nitride
更新于2025-09-23 15:21:01
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Modifying the geometric and electronic structure of hexagonal boron nitride on Ir(111) by Cs adsorption and intercalation
摘要： Epitaxial hexagonal boron nitride on Ir(111) is significantly modified by adsorption and intercalation of alkali-metal atoms. Regarding geometry, intercalation lifts the two-dimensional layer from its substrate and reduces the characteristic corrugation imprinted by direct contact with the metal substrate. Moreover, the presence of charged species in close proximity to the hexagonal boron nitride (hBN) layer strongly shifts the electronic structure (valence bands and core levels). We used scanning tunneling microscopy, low-energy electron diffraction, x-ray photoelectron spectroscopy (XPS), and the x-ray standing wave technique to study changes in the atomic structure induced by Cs adsorption and intercalation. Depending on the preparation, the alkali-metal atoms can be found on top and underneath the hexagonal boron nitride in ordered and disordered arrangements. Adsorbed Cs does not change the morphology of hBN/Ir(111) significantly, whereas an intercalated layer of Cs decouples the two-dimensional sheet and irons out its corrugation. XPS and angle-resolved photoelectron spectroscopy reveal a shift of the electronic states to higher binding energies, which increases with increasing density of the adsorbed and intercalated Cs. In the densest phase, Cs both intercalates and adsorbs on hBN and shifts the electronic states of hexagonal boron nitride by 3.56 eV. As this shift is not sufficient to move the conduction band below the Fermi energy, the electronic band gap must be larger than 5.85 eV.
关键词： hexagonal boron nitride,Cs adsorption,electronic structure,geometric structure,intercalation
更新于2025-09-23 15:21:01
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Probing hyperbolic polaritons using infrared attenuated total reflectance micro-spectroscopy
摘要： Hyperbolic polariton modes are highly appealing for a broad range of applications in nanophotonics, including surfaced enhanced sensing, sub-diffractional imaging, and recon?gurable metasurfaces. Here we show that attenuated total re?ectance (ATR) micro-spectroscopy using standard spectroscopic tools can launch hyperbolic polaritons in a Kretschmann–Raether con?guration. We measure multiple hyperbolic and dielectric modes within the naturally hyperbolic material hexagonal boron nitride as a function of different isotopic enrichments and ?ake thickness. This overcomes the technical challenges of measurement approaches based on nanostructuring, or scattering scanning near-?eld optical microscopy. Ultimately, our ATR approach allows us to compare the optical properties of small-scale materials prepared by different techniques systematically.
关键词： Hyperbolic polaritons,infrared attenuated total re?ectance micro-spectroscopy,hexagonal boron nitride,Kretschmann–Raether con?guration
更新于2025-09-23 15:21:01
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Microwave assisted synthesis of boron and nitrogen rich graphitic quantum dots to enhance fluorescence of photosynthetic pigments
摘要： Energy transfer between quantum dots and biomolecules is of interest due to high absorption capacity and high quantum efficiency of quantum dots. Amongst all types of quantum dots, graphene and graphitic quantum dots have great potential for energy transfer studies due to their high biocompatibility and low toxicity. In this study, a simple route to synthesize boron and nitrogen rich graphitic quantum dots (C-BN) and boron carbon nitride (BCN) quantum dots is demonstrated. Quantum dots were synthesized in a domestic microwave oven. Composition of quantum dots was controlled by tuning initial mole ratio of boron and nitrogen precursors. As molar ratio of boron precursor was increased, formation of C-BN quantum dots was favoured. C-BN quantum dots were mainly composed of boron and nitrogen (with around 10 % carbon) in their main composition, and sized around 2 nm with bright photoluminescence. To the best of our knowledge, this is the first study which proposes a bottom-up synthesis method to synthesize C-BN quantum dots based on domestic microwaves. Also, treating photosynthetic pigments with quantum dots resulted in 20 % enhancement of fluorescence of photosynthetic pigments at 670 nm, which demonstrates that C-BN and BCN quantum dots can be important constituents of artificial antenna systems for photosynthetic organisms.
关键词： Photosynthetic pigments,Boron nitride,Energy transfer,Graphitic quantum dots
更新于2025-09-23 15:19:57
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Conversionless efficient and broadband laser light diffusers for high brightness illumination applications
摘要： Laser diodes are efficient light sources. However, state-of-the-art laser diode-based lighting systems rely on light-converting inorganic phosphor materials, which strongly limit the efficiency and lifetime, as well as achievable light output due to energy losses, saturation, thermal degradation, and low irradiance levels. Here, we demonstrate a macroscopically expanded, three-dimensional diffuser composed of interconnected hollow hexagonal boron nitride microtubes with nanoscopic wall-thickness, acting as an artificial solid fog, capable of withstanding ~10 times the irradiance level of remote phosphors. In contrast to phosphors, no light conversion is required as the diffuser relies solely on strong broadband (full visible range) lossless multiple light scattering events, enabled by a highly porous (>99.99%) non-absorbing nanoarchitecture, resulting in efficiencies of ~98%. This can unleash the potential of lasers for high-brightness lighting applications, such as automotive headlights, projection technology or lighting for large spaces.
关键词： high-brightness illumination,solid-state lighting,light diffusers,laser diodes,hexagonal boron nitride
更新于2025-09-23 15:19:57
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Preparation of highly thermally conductive and electrically insulating PI/BNNSs nanocomposites by hot-pressing self-assembled PI/BNNSs microspheres
摘要： Traditional polymer-based thermally conductive composites with randomly distributed fillers always yield an undesired heat removal due to the lack of efficient heat transfer pathways. Thus, realization of rational and ordered distribution of thermally conductive nanofillers in polymer matrix is believed to be significant for obtaining a desirable thermal conductivity. Herein, a series of thermally conductive polyimide/boron nitride nanosheets (PI/BNNSs) composites with a highly ordered BNNSs network have been successfully prepared. For achieving an uniform dispersion and high orientation of BN nanosheets in PI matrix, self-assembled PI/BNNSs complex microspheres were firstly prepared via the van der Waals interaction, and then these complex microspheres were further hot-pressed at the Tg of PI matrix, which rendered the alignment of BNNSs during the deformation of complex microspheres and built an efficient heat transfer pathway. As a consequence, the resultant composites possess a much higher in-plane thermal conductivity up to 4.25 W/mK with 12.4 vol% oriented BNNSs than those of pure PI and random distribution composite (0.85 W/mK for pure PI and 1.3 W/mK for the PI/random BNNSs-12.4). Meanwhile, these nanocomposites present excellent electrically insulating properties, improved dimensional stabilities and good thermal stabilities. This facile method provides a new way to design and fabricate highly thermally conductive PI-based composites for applying in heat dissipation of modern portable and collapsible electronic devices.
关键词： Boron nitride nanosheets,Polyimide,Complex microspheres,Hot-pressing,Filler orientation
更新于2025-09-23 15:19:57
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van der Waals heterostructures combining graphene and hexagonal boron nitride
摘要： As the first in a large family of 2D van der Waals (vdW) materials, graphene has attracted enormous attention owing to its remarkable properties. The recent development of simple experimental techniques for combining graphene with other atomically thin vdW crystals to form heterostructures has enabled the exploration of the properties of these so-called vdW heterostructures. Hexagonal boron nitride is the second most popular vdW material after graphene, owing to the new physics and device properties of vdW heterostructures combining the two. Hexagonal boron nitride can act as a featureless dielectric substrate for graphene, enabling devices with ultralow disorder that allow access to the intrinsic physics of graphene, such as the integer and fractional quantum Hall effects. Additionally, under certain circumstances, hexagonal boron nitride can modify the optical and electronic properties of graphene in new ways, inducing the appearance of secondary Dirac points or driving new plasmonic states. Integrating other vdW materials into these heterostructures and tuning their new degrees of freedom, such as the relative rotation between crystals and their interlayer spacing, provide a path for engineering and manipulating nearly limitless new physics and device properties.
关键词： quantum Hall effect,graphene,moiré superlattices,polaritons,hexagonal boron nitride,van der Waals heterostructures
更新于2025-09-19 17:15:36
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Thickness-tunable growth of ultra-large, continuous and high-dielectric h-BN thin films
摘要： The outstanding thermal properties, mechanical properties and large optical bandgap of hexagonal boron nitride (h-BN) make it very attractive for various applications in ultrathin 2D microelectronics. However, the synthesis of large lateral size and uniform h-BN thin films with a high breakdown strength still remains a great challenge. Here, we comprehensively investigated the effect of growth conditions on the thickness of h-BN films via low pressure chemical vapor deposition (LPCVD). By optimizing the LPCVD growth parameters with electropolished Cu foils as the deposition substrates and developing customized "enclosure" quartz-boat reactors, we achieved thickness-tunable (1.50–10.30 nm) growth of h-BN thin films with a smooth surface (RMS roughness is 0.26 nm) and an ultra-large area (1.0 cm × 1.0 cm), meanwhile, the as-grown h-BN films exhibited an ultra-high breakdown strength of ~10.0 MV cm?1, which is highly promising for the development of electrically reliable 2D microelectronic devices with an ultrathin feature.
关键词： dielectric breakdown strength,h-BN,thin films,LPCVD,2D microelectronics,hexagonal boron nitride
更新于2025-09-19 17:15:36
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Anisotropic Flow Control and Gate Modulation of Hybrid Phonon-Polaritons
摘要： Light-matter interaction in two-dimensional photonic materials allows for confinement and manipulation of free-space radiation in sub-wavelength scales. Most notably, the van der Waals heterostructure comprising graphene (G) and hexagonal Boron Nitride (hBN) provides for gate-tunable hybrid hyperbolic plasmon phonon-polaritons (HP3). Here, we present anisotropic flow control and gate voltage modulation of HP3 modes in G-hBN lying on air-Au microstructured substrate. Using broadband infrared synchrotron radiation coupled to a scattering-type near-field optical microscope, we launch HP3 waves in both hBN Reststrahlen bands and observe directional propagation across in-plane heterointerfaces created at the air-Au junction. HP3 hybridization is modulated by varying the gate voltage between graphene and Au. In this case, we induce modifications to the coupling of continuum graphene plasmons with the discrete hBN hyperbolic phonon polaritons, which is interpreted as an extended Fano model. This is the first demonstration of control of polariton propagation, including a theoretical approach for a break of the reflection/transmission symmetry for HP3 modes. Our findings augment the degree of control of polaritons in G-hBN and related hyperbolic metamaterial nanostructures bringing novel insights to on-chip nano-optics communication and computing.
关键词： polaritonics,nano-photonics,graphene/boron nitride,near-field optics,hybrid polaritons,synchrotron infrared
更新于2025-09-19 17:15:36