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Decoding the structure of interfaces and impurities in 2D materials by photoelectron holography
摘要： The properties of atomically thin materials essentially depend on their structures, including impurities, defects and interfaces with underlying substrates. Thus, the detailed structural information is relevant for creation of 2D materials with desired properties. Here, we explore the capabilities of photoelectron diffraction and holography for structural analysis of atomically thin layers using as examples such systems as h-BN, graphene, and modified graphene with boron impurities. We show that for planar 2D crystals with commensurate interface to the substrate, it is possible to visualize the interface and impurities with high spatial resolution, and to distinguish possible non-equivalent structural units. Our approach applied to B-doped graphene on Ni(1 1 1) and Co(0 0 0 1) surfaces has allowed to reveal asymmetry of boron concentrations in the two carbon sublattices and established its dependence on the applied synthesis procedure and chosen substrate. The obtained results suggest that such approach can be widely applied for studies of various 2D systems, where the structures of interfaces and defects are of remarkable importance.
关键词： doping,structure,photoelectron diffraction,graphene,hexagonal boron nitride,photoelectron holography
更新于2025-09-19 17:13:59
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Controlled surface modification of poly(methyl methacrylate) film by fluoroalkyl end-capped vinyltrimethoxysilane oligomeric silica/hexagonal boron nitride nanocomposites
摘要： Fluoroalkyl end-capped vinyltrimethoxysilane oligomer [RF-(CH2CHSi(OMe)3)n-RF; n = 2, 3; RF = CF(CF3)OC3F7] undergoes sol–gel reactions in the presence of hexagonal boron nitride (h-BN) nanoparticles under alkaline or acidic conditions at room temperature to afford the corresponding fluorinated oligomeric silica/h-BN nanocomposites in good isolated yields (≥ 80%), respectively. The fluorinated oligomeric silica/h-BN nanocomposites thus obtained were found to exhibit a good dispersibility toward the traditional organic media including water. These two kinds of fluorinated nanocomposites were applied to the surface modification of poly(methyl methacrylate) (PMMA). The fluorinated nanocomposites prepared under alkaline conditions can give not only a good oleophobic characteristic imparted by longer fluoroalkyl groups in the composites but also the higher fluorescent emission related to the presence of h-BN on the only surface side of the modified PMMA film. In contrast, the fluorinated nanocomposites prepared under acidic conditions can provide a good oleophobic characteristic and a higher fluorescent emission on both the surface and even on the reverse side of the PMMA film. Such unique controlled surface modification ability will be discussed by 29Si solid-state NMR spectra of these two types of the nanocomposites.
关键词： Surface arrangement ability,Fluorescent ability,Oleophobicity,Hexagonal boron nitride,Surface modification,Fluorinated oligomeric nanocomposite,PMMA
更新于2025-09-16 10:30:52
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Probing Polaritons in 2D Materials with Synchrotron Infrared Nanospectroscopy
摘要： Polaritons, which are quasiparticles composed of a photon coupled to an electric or magnetic dipole, are a major focus in nanophotonic research of van der Waals (vdW) crystals and their derived 2D materials. For the variety of existing vdW materials, polaritons can be active in a broad range of the electromagnetic spectrum (meVs to eVs) and exhibit momenta much higher than the corresponding free-space radiation. Hence, the use of high momentum broadband sources or probes is imperative to excite those quasiparticles and measure the frequency-momentum dispersion relations, which provide insights into polariton dynamics. Synchrotron infrared nanospectroscopy (SINS) is a technique that combines the nanoscale spatial resolution of scattering-type scanning near-field optical microscopy with ultrabroadband synchrotron infrared radiation, making it highly suitable to probe and characterize a variety of vdW polaritons. Here, the advances enabled by SINS on the study of key photonic attributes of far- and mid-infrared plasmon- and phonon-polaritons in vdW and 2D crystals are reviewed. In that context the SINS technique is comprehensively described and it is demonstrated how fundamental polaritonic properties are retrieved for a range of atomically thin systems including hBN, MoS2, graphene and 2D heterostructures.
关键词： s-SNOM,hexagonal boron nitride,far-infrared SINS,2D materials,polaritons,infrared synchrotron nanospectroscopy,graphene
更新于2025-09-12 10:27:22
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Pt Nanoclusters Sandwiched between Hexagonal Boron Nitride and Nanographene as van der Waals Heterostructures for Optoelectronics
摘要： We report on the formation of nanoscopic heterostructures composed of the semimetal graphene, the metal platinum, and the insulator hexagonal boron nitride (h-BN). Both graphene and h-BN are chemically inert 2D materials with similar geometric but different electronic properties. Between these materials, a Pt nanoparticle array was encapsulated. Thereby, the h-BN/Rh(111) nanomesh served as a template for a well-ordered array of Pt nanoclusters, which were overgrown with graphene, forming single nano-heterostructures. We investigated this process in situ by high-resolution, synchrotron radiation-based XPS, and NEXFAS. The nanographene layers proofed tight against CO under the tested conditions. These nano-heterostructures could find a possible application in optoelectronics or as data storage material. At the same time, our approach represents a new route for the synthesis of nanographene.
关键词： nanoclusters,optoelectronics,hexagonal boron nitride,nanographene,data storage,graphene,platinum
更新于2025-09-12 10:27:22
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[IEEE 2019 IEEE 32nd International Conference on Micro Electro Mechanical Systems (MEMS) - Seoul, Korea (South) (2019.1.27-2019.1.31)] 2019 IEEE 32nd International Conference on Micro Electro Mechanical Systems (MEMS) - High-Frequency Hexagonal Boron Nitride (h-BN) Phononic Waveguides
摘要： This digest paper presents the first experimental demonstration of nanoscale phononic waveguides based on a two-dimensional (2D) layered crystalline material, namely hexagonal boron nitride (h-BN). Taking advantage of the planar geometry, the challenges in nanofabrication of 2D materials can be circumvented through a heterogeneous integration approach. Rich wave propagation characteristics of h-BN phononic waveguides are revealed in both finite element method (FEM) simulations and transmission measurements. Numerical analysis further indicates that the frequency response of the designed h-BN phononic waveguides can be finely tuned by varying the thickness or tension level of the h-BN crystals, across the high frequency (HF, 3?30 MHz) to very high frequency (VHF, 30?300 MHz) bands. Manipulation and guiding of high frequency mechanical waves on integratable 2D device platforms will open new opportunities in radio-frequency (RF) signal processing and on-chip quantum information technologies.
关键词： phononic waveguides,very high frequency (VHF),radio-frequency (RF) signal processing,quantum information technologies,high frequency (HF),hexagonal boron nitride (h-BN)
更新于2025-09-12 10:27:22
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Tunable reflected group delay from the graphene/hBN heterostructure at infrared frequencies
摘要： In this paper, we theoretically investigated the re?ected group delay from the graphene/hexagonal boron nitride (hBN) heterostructure in the infrared band. Since the signi?cant Lorentz resonance characteristic of the dielectric constant of hBN in the bands of near 7.28 μm and 12.72 μm, the new graphene/hBN heterostructure is used to realize ?exible switching of re?ected group delay by the Lorentz resonance mechanism. It is shown that the re?ected group delay can be e?ectively enhanced by tuning the Fermi energy or the number of graphene layers. Moreover, the re?ected group delay can be tuned positive or negative depending on the hBN thickness or incident angle. These results will be useful for design of graphene-based optical delay devices in the infrared band.
关键词： Graphene,Hexagonal boron nitride (hBN),Group delay,Infrared band
更新于2025-09-12 10:27:22
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Fabrication and characterization of quantum dot devices based on tetralayer graphene/hexagonal boron nitride heterostructures
摘要： We report on low temperature carrier transport property of quantum dot devices based on hexagonal boron nitride-encapsulated tetralayer graphene heterostructures. In the device with single dot geometry, we demonstrate a stochastic Coulomb blockade, suggesting formation of multiple dots coupled each other in series/parallel. Under a perpendicular magnetic field, the overlapping Coulomb diamonds are lifted at zero bias voltage and the charging energy is decreased. These imply the suppression of multiple dots behavior. Our results pave a way toward the investigation of interlayer correlation on single electron transport in few-layer graphene quantum dots.
关键词： magnetic field,hexagonal boron nitride,Coulomb blockade,tetralayer graphene,quantum dot
更新于2025-09-12 10:27:22
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Oxidising and carburising catalyst conditioning for the controlled growth and transfer of large crystal monolayer hexagonal boron nitride
摘要： Hexagonal boron nitride (h-BN) is well-established as a requisite support, encapsulant and barrier for 2D material technologies, but also recently as an active material for applications ranging from hyperbolic metasurfaces to room temperature single-photon sources. Cost-effective, scalable and high quality growth techniques for h-BN layers are critically required. We utilise widely-available iron foils for the catalytic chemical vapour deposition (CVD) of h-BN and report on the significant role of bulk dissolved species in h-BN CVD, and specifically, the balance between dissolved oxygen and carbon. A simple pre-growth conditioning step of the iron foils enables us to tailor an error-tolerant scalable CVD process to give exceptionally large h-BN monolayer domains. We also develop a facile method for the improved transfer of as-grown h-BN away from the iron surface by means of the controlled humidity oxidation and subsequent rapid etching of a thin interfacial iron oxide; thus, avoiding the impurities from the bulk of the foil. We demonstrate wafer-scale (2”) production and utilise this h-BN as a protective layer for graphene towards integrated (opto-)electronic device fabrication.
关键词： monolayer,hexagonal boron nitride,transfer,2D materials,large crystal,chemical vapor deposition,encapsulation
更新于2025-09-12 10:27:22
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Effects of Hexagonal Boron Nitride Sheets on the Optothermal Performances of Quantum Dots-Converted White LEDs
摘要： Recently, quantum dots-converted white light-emitting diodes (QDs-WLEDs) are attracting numerous attention due to their high luminous efficiency and excellent color quality. As for color conversion material, the quantum dots (QDs) are commonly embedded into a low-thermal-conductivity polymer matrix. In this case, their generated heat during the photoluminescence process can hardly be dissipated into the heat sink, leading to a high working temperature and reduced lifetime. Adding particles with high thermal conductivity to the QDs layer can enhance its thermal conductivity, and thus reduce QDs’ working temperature. At the same time, these particles may affect the optical properties of QDs. However, this problem has still not been deeply studied. In this article, we systematically investigated the effects of the highly thermal-conductive hexagonal boron nitride sheets (hBNSs) on the optothermal performances of QDs/phosphor film in white light-emitting diodes (WLEDs). The thermal conductivity of QDs/phosphor film was significantly increased by 24% after adding 5wt% of 45-μm-diameter hBNS. As for the optical performance, the transparency of the silicone gel film with 45-μm-diameter hBNS was much better than that with 6–9-μm-diameter hBNS under the same weight fraction. Furthermore, the scattering effect of hBNS plays a more important role in enhancing the light conversion performance of QDs than that of phosphor. At last, a color stability test showed the increasing rate of correlated color temperature (IRCCT) of hBNS-added WLEDs are 21% smaller than that of common WLEDs after working 153 h, meaning a better QDs stability in hBNS-added WLEDs.
关键词： light conversion,quantum dots (QDs),Hexagonal boron nitride sheets (hBNSs),thermal conductivity
更新于2025-09-11 14:15:04
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Cataluminescence coupled with photo-assisted technology: a highly efficient metal-free gas sensor for carbon monoxide
摘要： With the development of green chemistry, metal-free nano-catalysts have gradually substituted metal-based materials, causing widespread concern among researchers in many fields, especially in cataluminescence sensing, because of their long-term stability, environmental friendliness as well as low costs. Besides the catalysts, the innovations of assistant technologies for cataluminescence are needed to enhance the oxidation reactivity of the gas molecules or catalytic efficiency of sensing materials. Although, there are some groups enhancing the cataluminescence reaction via various assistant technologies, the development of assistant technologies in cataluminescence sensors are still in their infancy, the design, effect mechanism and application are still stimulating challenges. Herein, with photodynamic assistant, fluorinated nanoscale hexagonal boron nitride is first employed as a metal-free catalyst to establish a novel cataluminescence method for detecting CO gases, and the cataluminescence reaction mechanism of CO is also investigated in details. Under the best conditions, the detection limit (3σ) of the CO concentration is 0.005 μg mL-1, which has been largely improved in cataluminescence methods. The realization of detection of CO from theory to practice thorough the method of cataluminescence is beneficial of the practical application of metal-free catalysts to detect CO rather than stay at the possibility to detect CO by the means of theoretical calculation only.
关键词： metal-free gas sensor,carbon monoxide,Cataluminescence,fluorinated hexagonal boron nitride,photo-assisted technology
更新于2025-09-11 14:15:04