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Dielectric Anisotropy Sensor Using Coupled Resonators
摘要： In this article, a new approach is proposed for the measurement of the uniaxial anisotropic dielectric constant of different planar samples by means of a single sensor. The sensor is based on a couple of straight-line coupled resonators in microstrip technology that can be excited in odd and even propagation modes. This sensor is designed on an isotropic substrate at the design frequency. Due to the electric field configuration specific for each mode, it is possible to relate these modes to the dielectric constant in two different directions (parallel and perpendicular) of a dielectric material placed on top of the sensor. This technique is used for the successful characterization of the dielectric constant anisotropic of anisotropic dielectrics (FR4, Rogers 4350B, and Arlon Diclad 880), and the isotropic material PTFE.
关键词： FR4,Anisotropic,dielectric constant,printed circuit board (PCB),uniaxial,anisotropy,sample under test (SUT)
更新于2025-09-16 10:30:52
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Evaluation of internal defects generated in machine milled carbon fiber reinforced plastic using X-ray computed tomography
摘要： In this study, X-ray computed tomography (X-ray CT) was used to investigate internal defects generated on machine milled carbon fiber reinforced plastics (CFRP). Internal defects such as cracks, fractures, and deformation of the carbon fibers, which are invisible from the surface, were observed using the X-ray CT method. Defects were generated based on the machining method and direction of the fibers. A large number of defects were generated when using the conventional cut method along 45°, 90°, and the climb cut method along 90°. Few internal defects were observed when using the climb cut method along 45°; however, the machined surface was very rough. The mechanism for these phenomena was investigated by studying surface observations and cutting force, in addition to X-ray CT imaging. These results indicate that X-ray CT is a powerful tool for visualizing internal defects in CFRP, which differ significantly based on the direction of the fiber and machining method used.
关键词： Carbon fiber reinforced plastics,Surface roughness,Milling,Internal defect,X-ray computed tomography
更新于2025-09-16 10:30:52
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Atomic-Level Microstructure of Efficient Formamidinium-Based Perovskite Solar Cells Stabilized by 5-Ammonium Valeric Acid Iodide Revealed by Multi-Nuclear and Two-Dimensional Solid-State NMR
摘要： Chemical doping of inorganic-organic hybrid perovskites is an effective way of improving the performance and operational stability of perovskite solar cells (PSCs). Here we use 5-ammonium valeric acid iodide (AVAI) to chemically stabilize the structure of α-FAPbI3. Using solid-state MAS NMR, we demonstrate the atomic-level interaction between the molecular modulator and the perovskite lattice and propose a structural model of the stabilized three-dimensional structure, further aided by density functional theory (DFT) calculations. We find that one-step deposition of the perovskite in the presence of AVAI produces highly crystalline films with large, micrometer-sized grains and enhanced charge-carrier lifetimes, as probed by transient absorption spectroscopy. As a result, we achieve greatly enhanced solar cell performance for the optimized AVA-based devices with a maximum power conversion efficiency (PCE) of 18.94%. The devices retain 90% of the initial efficiency after 300 h under continuous white light illumination and maximum-power point-tracking measurement.
关键词： power conversion efficiency,density functional theory,perovskite solar cells,chemical doping,solid-state MAS NMR,charge-carrier lifetimes,5-ammonium valeric acid iodide
更新于2025-09-16 10:30:52
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Synergistic effect of fluorescence recovery and enhancement on ultrasensitive visual assay of cyanide anions based on N-Acetyl-L-Cysteine-Capped CdTe quantum dots and carbon dots
摘要： Developing a reliable fluorescent nanosensor for cyanide anions (CN?), with the potential to enable visual discrimination by naked eye, is highly sought after yet is limited by low sensitivity and selectivity. Herein based on the synergistic effect of fluorescence recovery and enhancement, a specific dual-emission nano-system was designed for ultrasensitive detection of CN?, by employing carbon dots (peaking at 443 nm) as a reference and N-acetyl-L-cysteine (NALC)-capped CdTe quantum dots (QDs, peaking at 611 nm) as a reporter. The red fluorescence of CdTe QDs is first quenched by Cu2+ primarily with electron transfer. Upon addition of CN?, coordinates with Cu2+ to form [Cu(CN)n](n?1)? complex, causing the Cu2+ to detach from the QDs, and consequently fluorescence recovery. More importantly, the CN? can undergo a nucleophilic addition reaction with the carbonyl group of NALC ligands, inducing 1.3-fold fluorescence enhancement towards the original QDs while the blue fluorescence of carbon dots remains constant. This results the fluorescence intensity ratios (I611/I443) are proportional to the concentrations of CN? in the ranges of 0.02―10 and 15―80 μM, and an ultra-low detection limit down to 10.35 nM is achieved. By using both Cu2+-promoted complexation and addition reaction as recognition units, the present method also showed excellent selectivity for CN? over other coexisting anions. Especially, we have already demonstrated, by spiked tests, the practicability of monitoring the concentration changes of CN? in both environmental water and cassava samples, and further realized visual monitoring of CN? changes in aqueous solution and test paper.
关键词： Ratiometric detection,Visual identification,Nucleophilic addition,Quantum dots,Turn-on,Cyanide anions
更新于2025-09-16 10:30:52
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Controlled gradual and local thinning of free-standing nanometer thick Si3N4 films using reactive ion etch
摘要： Nanometer-scale devices are fabricated using numerous fabrication techniques since the last couple of decades. However, the advancement in nanotechnology gives new horizons to the researcher to develop nanometer-scale devices in a controlled manner while also providing high accuracy and precision with cost and time-effectiveness. This article focuses on the production of free-standing nano-scale thick Si3N4 films using Reactive Ion Etch technique. Although there are many reports in the literature on the required conditions to etch Si3N4, unfortunately, there are not many technical reports that illustrate the step-by-step fabrication and characterization together with the detailed optimization steps. Here in this study, the thinning of a membrane is achieved using CF4/Ar in controlled RF power conditions and a well-defined protocol is given with several preliminary optimization steps. By doing so, free-standing locally thinned Si3N4 membranes of about 20 nm thickness are successfully realized in a precise manner. Further assessments are given an offer to the readers of interest the ways to characterize the samples with the required cautions. The detailed procedure given here would potentially provide practical aspects for the researchers working in the field of nanofabrication.
更新于2025-09-12 10:27:22
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Pink all-inorganic halide perovskite nanocrystals with adjustable characteristics: Fully reversible cation exchange, improving the stability of dopant emission and light-emitting diode application
摘要： In this work, we proposed a straightforward and effective strategy for preparing pink all-inorganic halide perovskite nanocrystal (NC) phosphors for light-emitting diode (LED) application. The pink perovskite NCs with varying Mn contents could be easily and steadily obtained via postsynthetic ion exchange at room temperature. The dependence of the size and optical properties of pink NCs on dopant content was systematically investigated. The reversible anion exchange processes of pink perovskite NCs were conducted with halide salts containing or excluding Pb. The contrasting results suggested that the irreversibility of Mn-emission was mainly affected by the fully reversible cation exchange between Pb2+ and Mn2+. The pink NCs with better stability of dopant emission and high monodispersity were successfully developed by compounding with silica. A pink LED was further made by using the pink NCs/silica composites as pink phosphors on a 395 nm InGaN LED chip. This work provides a feasible strategy for the fabrication of pink LEDs, which may have great application prospects in the field of special lighting, like neon lights and plant growth lights.
关键词： light-emitting diodes,anion exchange,perovskite nanocrystals,stability,cation exchange
更新于2025-09-12 10:27:22
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Pyridine-hydrazone-controlled cyanide detection in aqueous media and solid-state: tuning the excited-state intramolecular proton transfer (ESIPT) fluorescence modulated by intramolecular NH?Br hydrogen bonding
摘要： A new efficient pyridine-hydrazone-substituted naphthalimide receptor 4a-E has been synthesized as a selective colorimetric and fluorescent chemosensor for cyanide sensing in aqueous environments through a unique excited-state intramolecular proton transfer (ESIPT) mechanism. The addition of a Br group to the fluorophore skeleton at the ortho-position of hydrazone generates reference compounds (4b-E and 4c-Z). Interestingly, the potential intramolecular NH?Br hydrogen bonding might compete with the anion-induced intermolecular NH?A? hydrogen bonding, resulting in dramatic ESIPT suppression. The high emission of probe 4a-E and other control probes in solid-state is also investigated. Moreover, probe 4a-E preloaded on test papers, upon cyanide treatment, shows obvious changes in color which demonstrates that 4a-E is a writable platform. More importantly, it exhibits great potential application for the detection of cyanide in food materials and excellent performance in real-world water samples.
关键词： ESIPT,colorimetric,pyridine-hydrazone,fluorescent chemosensor,cyanide sensing
更新于2025-09-12 10:27:22
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Solution-Processible Blue Fluorescent Dendrimers with Carbazole/Diphenylamine Hybrid Dendrons for Power-Efficient Organic Light-Emitting Diodes
摘要： Two blue ?uorescent dendrimers named PVAC2 and PVACA have been newly synthesized and investigated, where the carbazole/diphenylamine hybrid dendron is adopted instead of oligocarbazole. Compared with the reference dendrimer PVCt3, the emission maxima of PVAC2 and PVACA are found to be red-shifted accompanied by a slight reduction of the photoluminescence quantum yield in ?lms. Most importantly, the highest occupied molecular orbital level is elevated from ?5.35 eV of PVCt3 to ?5.20 eV of PVAC2 and ?4.95 eV of PVACA. Because of the favored hole injection, the turn-on voltage is accordingly decreased from 3.6 to 3.2 and 2.6 V. The value of PVACA is even lower than the theoretical limit of 2.78 V. In addition, PVAC2 exhibited the best nondoped device performance, showing a nearly doubled power e?ciency of 4.80 lm/W relative to PVCt3 (2.37 lm/W). The results clearly indicate that dendron engineering is also a promising strategy to develop solution-processible blue ?uorescent dendrimers capable of being used for power-e?cient organic light-emitting diodes.
关键词： solution-processible,blue fluorescent dendrimers,power-efficient organic light-emitting diodes,carbazole/diphenylamine hybrid dendron
更新于2025-09-12 10:27:22
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Controlled etching of silica nanospheres monolayer for template application: A systematic study
摘要： Monolayers of silica nanospheres (SNs), via self- or guided-assembly has been extensively used for template fabrication in thin films, employed in the areas of plasmonics, photonic crystals, and solar cells. We report on a versatile, rapid, and controllable process to obtain non-close-packed structure by restructuring the SNs geometry at two-particle level. A geometrical model has been proposed to quantify parameters that control the final morphology of the monolayer. SNs of different sizes (viz. 140 nm, 170 nm, and 220 nm) were self-assembled as a close-packed monolayer on a silicon substrate using a three-step spin coating method and then sintered at 950oC before being exposed to an etchant. We investigate the dependence of particle radius, neck (formed due to sintering) parameters and distance between the SNs, on etching time and etchant concentration. The intermediate and final morphology of the restructured monolayer is used as a template to grow silicon nanowires using metal-assisted chemical etching. We provide quantitative estimates of the parameters pertaining to the restructuring of the monolayer of SNs, which can be used as tunable templates for the growth of nanowires. The optimized process can be scaled-up for industrial application because of its faster and controllable rate of production.
关键词： Silica Nanospheres,Sintering,Etching,Non-Close-Packed Monolayer,Self-Assembly
更新于2025-09-12 10:27:22
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Novel Dicyano-Phenylenevinylene Fluorophores for Low-Doped Layers: A Highly Emissive Material for Red OLEDs
摘要： Two efficient deep red (DR)-emitting organic dicyano-phenylenevinylene derivatives with terminal withdrawing or donor groups were synthesized. The spectroscopic properties of the neat solids and the low-doped layers in polystyrene or polyvinylcarbazole host matrixes were analyzed, and the luminescence performance was explained using density functional theory (DFT) analysis. A noteworthy 89% fluorescence quantum yield was observed for the brightest red-emissive polyvinylcarbazole (PVK) blend. This result pushed us to successfully produce an emissive red organic light-emitting device (OLED) as a preliminary feasibility test.
关键词： dicyano-phenylenevinylene,fluorophore,aggregation-caused quenching (ACQ),OLED,DR
更新于2025-09-11 14:15:04