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Metasurface for Constructing a Stable High- <i>Q</i> Plano-Planar Open Cavity
摘要： Traditional open cavities are constructed by planar or concave mirrors. A Fabry–Pérot (FP) cavity is convenient to integrate and fabricate, but highly sensitive to the parallelism of the end mirrors. In contrast, a concave cavity is more stable and possesses a lower leaky rate, but the curved geometry brings inconvenience. Here, it is suggested that a planar meta-cavity can simultaneously possess the advantages of both of the above open cavities by using a metasurface to create a planar meta-mirror that mimics the behavior of a concave mirror. For demonstration, a microwave meta-cavity is constructed, whose meta-mirror consists of subwavelength ceramic blocks on a metal substrate. Compared to an FP cavity, the meta-cavity is more robust against the alignment error of the end mirrors, and 15-fold enhancement of the quality factor is observed numerically. Experimental results are in good agreement with the simulated results. The suggested method may be extended to work in high frequency ranges. This work would support the planarization and miniaturization of an open cavity and may also increase the functionality.
关键词： open cavities,cavity stability,high quality factor,metasurfaces
更新于2025-09-23 15:23:52
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Quality factor assessment of finite-size all-dielectric metasurfaces at the magnetic dipole resonance
摘要： Recently there has been a large interest in achieving metasurface resonances with large quality factors. In this article, we examine metasurfaces that comprised a finite number of magnetic dipoles oriented parallel or orthogonal to the plane of the metasurface and determine analytic formulas for their resonances’ quality factors. These conditions are experimentally achievable in finite-size metasurfaces made of dielectric cubic resonators at the magnetic dipole resonance. Our results show that finite metasurfaces made of parallel (to the plane) magnetic dipoles exhibit low quality factor resonances with a quality factor that is independent of the number of resonators. More importantly, finite metasurfaces made of orthogonal (to the plane) magnetic dipoles lead to resonances with large quality factors, which ultimately depend on the number of resonators comprising the metasurface. In particular, by properly modulating the array of dipole moments by having a distribution of resonator polarizabilities, one can potentially increase the quality factor of metasurface resonances even further. These results provide design guidelines to achieve a sought quality factor applicable to any resonator geometry for the development of new devices such as photodetectors, modulators, and sensors.
关键词： dipole approximation,Mie resonances,magnetic dipole resonance,finite-size metasurfaces,High quality factor
更新于2025-09-23 15:22:29
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Production of industry-specific quartz raw material using Sri Lankan vein quartz
摘要： High-purity quartz is a major raw material in many high-tech applications. Sri Lanka is rich in quartz mineralization, with an abundance of major vein quartz deposits with purity levels exceeding 99.5% SiO2. Developing high-tech products requires considerable capital investment, expertise, and advanced processing technologies which are lacking in developing countries like Sri Lanka. In most developing countries raw quartz with limited added value is exported to industrialized countries in grit and powder forms only after size reduction of run-of quarry quartz. We here examine an alternative approach, in which value addition is achieved by production of semi-processed and processed industry-specific quartz raw material for export. Chemical compositions of major types of vein quartz from seven vein quartz deposits and products of mass scale quartz processing at a plant located in the Badulla district of Uva Province, Sri Lanka were determined in study. Critical step evaluation in mining, transport and processing activities was carried out with reference to Fe and other critical trace elements, from data determined using inductively coupled plasma optical emission spectroscopy and atomic absorption spectroscopy. The results show that industrially critical trace element contents vary with type of quartz, association of accessory minerals, physical separation methods, transport practices, and comminution methods. We conclude that industry-specific quartz raw material can be produced through a combination of selective mining and exercising quality control during mining, transportation and processing activities.
关键词： Quartz,High-quality quartz,Quartz purification,Quartz raw material
更新于2025-09-23 15:22:29
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Environmentally Benign Metal-Free Reduction of GO Using Molecular Hydrogen: A Mechanistic Insight
摘要： A simple yet effective methodology to obtain high-quality reduced graphene oxide (RGO) using a tetrahydrofuran suspension of GO under hydrogen at moderate pressure has been demonstrated. The extent of reduction as a function of the pressure of hydrogen gas, temperature, and time was studied, where the abstraction of oxygen is achievable with least mutilation of C-sp2 bonds, hence upholding the integrity of the graphene sheet. Herein, the formation of a short-lived species is proposed, which is possibly responsible for such reduction. A detailed theoretical calculation along with in situ UV?visible experiments reveals the existence of a transient solvated electron species in the reaction medium. The hydrogen RGO (HRGO) achieved a C/O atomic ratio of 11.3. The conductivity measurements show that HRGO reached as high as 934 S/m, which indicates a high quality of RGO. The process is hassle-free, environmentally benign, and can be scaled up effortlessly without compromising the quality of the material.
关键词： reduced graphene oxide,high-quality RGO,environmentally benign,hydrogen reduction,solvated electron
更新于2025-09-23 15:21:21
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Graphene Quantum Dots with High Yield and High Quality Synthesized from Low Cost Precursor of Aphanitic Graphite
摘要： It is di?cult to keep the balance of high quality and high yield for graphene quantum dots (GQDs). Because the quality is uncontrollable during cutting large 2D nanosheets to small 0D nanodots by top-down methods and the yield is low for GQDs with high quality obtained from bottom-up strategy. Here, aphanitic graphite (AG), a low-cost graphite contains a large amount of small graphite nanocrystals with size of about 10 nm is used as the precursor of graphene oxide quantum dots (GO-QDs) for the ?rst time. GO-QDs with high yield and high quality were successfully obtained directly by liquid phase exfoliating AG without high strength cutting. The yield of these GO-QDs can reach up to 40 wt. %, much higher than that obtained from ?ake graphite (FG) precursor (less than 10 wt. %). The size of GO-QDs can be controlled in 2–10 nm. The average thickness of GO-QDs is about 3 nm, less than 3 layer of graphene sheet. Graphene quantum dots (GQDs) with di?erent surface properties can be easily obtained by simple hydrothermal treatment of GO-QDs, which can be used as highly e?cient ?uorescent probe. Developing AG as precursor for GQDs o?ers a way to produce GQDs in a low-cost, highly e?ective and scalable manner.
关键词： high yield,high quality,low cost precursor,aphanitic graphite,graphene quantum dots
更新于2025-09-23 15:21:01
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Room Temperature Graphene Mid-Infrared Bolometer with a Broad Operational Wavelength Range
摘要： The last decade has witnessed the realization of numerous different types of graphene photodetectors with a strong focus on the visible and near-infrared spectral range, in which various high-performance photodetectors exist based on traditional materials such as silicon and III-V compound semiconductors. However, high-speed mid-infrared photodetection at room-temperature is still an unsolved challenge, despite its importance in applications such as security, sensing, and imaging. Here we address this challenge by demonstrating that high-quality graphene is an ideal high-speed bolometric material for the less-explored yet critical mid-infrared photodetection at room temperature, due to its broadband absorption, small heat capacity, and remarkably large temperature coefficient of resistance (TCR) of up to around 1% per Kelvin, which is comparable to that of commercial bolometric materials. We demonstrate a device based on graphene encapsulated in hexagonal boron nitride (hBN) exhibiting decent extrinsic responsivities of 5.1-1.4 mA/W in 3.4-12 μm wavelength range at room temperature, and further predict a detection bandwidth of at least 47 MHz. Our demonstration lays the foundations for graphene high-speed mid-infrared technologies.
关键词： high-quality graphene,broad wavelength range,scattering channels,Mid-infrared bolometer,temperature coefficient of resistance
更新于2025-09-23 15:21:01
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Noise-robust transparent visualization of large-scale point clouds acquired by laser scanning
摘要： We propose a high-quality transparent visualization method suitable for large-scale laser-scanned point clouds. We call the method “stochastic point-based rendering (SPBR),” which is based on a novel stochastic algorithm. SPBR enables us to clearly observe the deep interior of laser-scanned 3D objects with the correct feeling of depth. The high quality of SPBR originates from the effect of “stochastic noise transparentization,” which is an effect to make the measurement noise transparent and invisible in the created images. We mathematically prove that this effect also makes the created transparent images coincide with the results of the conventional methods based on the alpha blending, which is time-consuming and impractical for large-scale laser-scanned point clouds. We also demonstrate the effectiveness of SPBR by applying it to modern buildings, cultural heritage objects, forests, and a factory. For all of the cases, the method works quite well, realizing clear and correct 3D see-through imaging of the laser-scanned objects.
关键词： High quality 3D see-through imaging,Laser-scanned point cloud,Large-scale data,Stochastic noise transparentization,Visualization
更新于2025-09-23 15:21:01
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Engineering of high quality factor THz metasurfaces by femtosecond laser ablation
摘要： We report on the realization of high Q metasurfaces operating in the THz frequency range by femtosecond laser ablation applied to a nanometric metallic layer over a silicon substrate. Two different fabrication methods are used to develop periodic patterns whose basic elements are in form of an array of through-holes or metallic islands. The response of the resulting structures is characterized using a time-domain spectrometer in the frequency range 0.3–1.5 THz. The experimental findings are compared with the predictions of full wave electromagnetic simulations. The fairly good agreement between simulation predictions and experimental findings evidences that the proposed approach can offer a facile way to the elaboration of THz metasurfaces.
关键词： Femtosecond laser ablation,THz,High quality factor,Metasurfaces
更新于2025-09-23 15:21:01
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Multi-scale fidelity measure for image fusion quality assessment
摘要： Image fusion is considered an effective enhancing methodology widely included in high-quality imaging systems. Nevertheless, like other enhancing techniques, output quality assessment is made within small sample subjective evaluation studies which are very limited in predicting the human-perceived quality of general image fusion outputs. Simple, blind, universal and perceptual-like methods for assessing composite image quality are still a challenge, partially solved only in particular applications. In this paper, we propose a fidelity measure, called MS-QW with two major characteristics related to natural image statistics framework: a multi-scale computation and a structural similarity score. In our experiments, we correlate the scores of our measure with subjective ratings and state of art measures included in the 2015 Waterloo IVC multi-exposure fusion (MEF) image database. We also use the measure to rank correctly the classical general fusion methods included in the Image Fusion Toolbox for medical, infra-red and multi-focus image examples. Moreover, we study the scores variability and statistical discrimination power with the TNO night vision database using the Friedman test. Finally, we define a new leave one out procedure based on our fidelity measure that selects the best subset of images (within a collection of distorted and unregistered cellphone type images) that provides a defect-free composite output. We exemplify the procedure with the fusion of a collection of images from Latour and Van Dongen paintings suffering from glass highlights and speckle noise, among other artifacts. The proposed multiscale quality measure MS-QW demonstrates improvement over the previous single-scale similarity measures towards a fidelity assessment between quantitative image fusion quality metrics and human perceptual qualitative scores.
关键词： structural similarity,statistical performance assessment,high quality photographs of paintings,multi-scale measures,image fusion quality assessment
更新于2025-09-19 17:15:36
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Transferable High-Quality Inorganic Perovskites for Optoelectronic Devices by Weak Interaction Heteroepitaxy
摘要： Transferable semiconductors with superior light-emitting properties are important for developing flexible and integrated optoelectronics. However, finding such a qualified candidate remains challenging. Here, we report the fabrication of transferable high-quality CsPbBr3 single-crystals on highly oriented pyrolytic graphite (HOPG) substrate via weak-interaction heteroepitaxy for the first time. Semi-quantitative kinetic analysis based on classical nucleation theory well accounts for the van der Waals (vdW) epitaxial growth process of perovskite on the HOPG substrate. The density functional theory (DFT) calculations illustrate the bonding nature of the interface and predict the Volmer-Weber growth mode in vdW epitaxy, which is consistent with our experimental observations. Importantly, the extremely weak vdW interaction between perovskite and HOPG not only enables the high quality of the crystals, but also endows them with the facile transferability to any foreign substrate by the mechanical exfoliation technique. Leveraging on the transferred CsPbBr3 single-crystals, the low-threshold microlasers and monolithic perovskite light-emitting diode (LED) devices are demonstrated. Our results represent a significant step towards advanced optoelectronic devices relying on the emerging perovskite semiconductors.
关键词： high quality,optoelectronic devices,heteroepitaxy,Transferable semiconductor,halide perovskite
更新于2025-09-19 17:13:59