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Waveguide optimization and its evaluation of a doped polymer optical ???ber designed for visual detection of stress
摘要： A fiber-optic strain sensor using a fluorophore-doped polymer optical fiber (POF) was fabricated at various waveguiding conditions. The effects attributed to each structural feature of the sensor were characterized by observing the sensor?s response. Two fluorophores, Coumarin 540A and Rhodamine 6G, were used to dope the core and the cladding of a poly(methyl methacrylate)-based POF, respectively. Using doped POFs with different numerical apertures (NAs), the changes in the fluorophore peaks upon the application of stress were analyzed by applying macrobending (s) to the fiber. Although the sensor response did not show linearity with respect to the NA, it was found that the shape of the Coumarin 540A-attributed peak was a factor that represented the sensor?s sensitivity. As a result, the double-cladding structure demonstrated its effectiveness in improving the stress sensitivity.
关键词： double-cladding structure,fluorophore-doped,polymer optical fiber,numerical aperture,fiber-optic strain sensor,stress sensitivity
更新于2025-09-23 15:21:01
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Deep Learning Enabled Strain Mapping of Single-Atom Defects in 2D Transition Metal Dichalcogenides with Sub-picometer Precision
摘要： 2D materials offer an ideal platform to study the strain fields induced by individual atomic defects, yet challenges associated with radiation damage have so-far limited electron microscopy methods to probe these atomic-scale strain fields. Here, we demonstrate an approach to probe single-atom defects with sub-picometer precision in a monolayer 2D transition metal dichalcogenide, WSe2-2xTe2x. We utilize deep learning to mine large datasets of aberration-corrected scanning transmission electron microscopy images to locate and classify point defects. By combining hundreds of images of nominally identical defects, we generate high signal-to-noise class averages which allow us to measure 2D atomic spacings with up to 0.2 pm precision. Our methods reveal that Se vacancies introduce complex, oscillating strain fields in the WSe2-2xTe2x lattice that correspond to alternating rings of lattice expansion and contraction. These results indicate the potential impact of computer vision for the development of high-precision electron microscopy methods for beam-sensitive materials.
关键词： scanning transmission electron microscopy,strain mapping,single-atom defects,Deep learning,fully convolutional network (FCN),2D materials
更新于2025-09-23 15:21:01
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Is Speckle Tracking Imaging Ready for Prime Time in Current Echo Clinical Practice?
摘要： Accurate assessment of left and right ventricular systolic function plays a fundamental role in the prognostication and management of patients with known or suspected cardiovascular disease. Traditional echocardiographic parameters, including left ventricular ejection fraction, may lack the sensitivity to detect subclinical left ventricular systolic dysfunction. The advent of speckle tracking echocardiography for left and right ventricular systolic function assessment provides a further tool in this evaluation. Speckle tracking echocardiography has been demonstrated to provide incremental prognostic value beyond traditional echocardiographic parameters. This review discusses the clinical application of speckle tracking echocardiography in the evaluation of cardiovascular disease and its implementation within the clinical echocardiography laboratory.
关键词： Speckle tracking echocardiography,Strain Echocardiography,Left ventricular systolic function,Right ventricular systolic function
更新于2025-09-23 15:21:01
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Graphene Foam: Hole-Flake Network for Uniaxial Supercompression and Recovery Behavior
摘要： We employed the coarse-grained molecular dynamics simulation method to systematically study the uniaxial supercompression and recovery behavior of multi-porous graphene foam, in which a mesoscopic three-dimensional network with hole-graphene flakes was proposed. The network model not only considers the physical cross-links and interlayer van der Waals interactions, but also introduces a hole in the flake to approach the imperfection of pristine graphene and the hierarchical porous configuration of real foam material. We first recreated a typical two-stage supercompression stress?strain relationship and the corresponding time-dependent recovery as well as a U-type nominal Poisson ratio. Then the recovery unloading at different strains and multicycle compression?uncompression were both conducted; the initial elastic moduli in the multicycles were found to be the same, and a multilevel residual strain was disclosed. Importantly, the residual strain is not exactly the plastic one, part of which can resurrect in the subsequent loading?unloading?holding. The mesoscopic mechanism of viscoelastic and residual deformation for the recovery can be attributed to the van der Waals repulsion and mechanical interlocking among the hole-flakes; interestingly, the local tensile stress was observed in the virial stress distribution. Particularly, an abnormal turning point in the length-time curve for the mean bead-bond length was captured during the supercompression. After the point, the length abnormally increases for different size ratios of the hole to the flake, which is in line with the mesostructure evolution. The finding may provide a mesoscopic criterion for the supercompression of graphene foam related materials.
关键词： supercompression,strain history,recovery behavior,mesoscale,van der Waals interaction,viscoelastoplasticity,graphene foam,coarse-grained molecular dynamics
更新于2025-09-23 15:21:01
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<i>Ab Initio</i> Spin-Strain Coupling Parameters of Divacancy Qubits in Silicon Carbide
摘要： Cubic silicon carbide is an excellent platform for integration of defect qubits into established wafer-scale device architectures for quantum information and sensing applications, where a divacancy qubit, which is similar to the negatively charged nitrogen-vacancy (NV) center in diamond, has favorable coherence properties. We demonstrate by means of density-functional-theory calculations that for most types of distortion the 3C divacancy exhibits slightly smaller spin-strain coupling parameters but greater spin-stress coupling parameters in comparison with the diamond NV. We predict that high-quality 3C-SiC thin films hosting divacancy qubits are prospective platforms for quantum-enhanced pressure-sensor devices.
关键词： spin-strain coupling,quantum sensing,density-functional theory,divacancy qubits,silicon carbide
更新于2025-09-23 15:21:01
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Determination of Phonon Deformation Potentials in Carbon-Doped Silicon
摘要： Carbon-doped silicon (Si:C) is used as a stressor to the channel of n-type metal oxide semiconductor field-effect-transistor (MOSFET). In this study, we determined PDPs, phonon deformation potentials, (p and q) of Si:C to realize evaluation of anisotropic biaxial stress by using water-immersion Raman spectroscopy. Raman peak shift in longitudinal and transverse optical (LO and TO) phonon modes were measured by water-immersion Raman spectroscopy. Furthermore, in-plane and out-of-plane strain were measured by X-ray diffraction (XRD). Based on the Raman shift and the in-plane strain, p and q in each sample were derived. As a result, it took a different value from pure-Si, and the PDPs tended to increase as the C concentration increased.
关键词： phonon deformation potentials,strain evaluation,Carbon-doped silicon,X-ray diffraction,water-immersion Raman spectroscopy
更新于2025-09-23 15:21:01
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X-Ray Analysis of Cadmium Oxide Nanostructured Films Synthesized with Different Precursor Molarities by Silar Method
摘要： Nanostructured cadmium oxide thin films have been synthesized onto suitably cleaned glass substrates by SILAR (successive ionic layer adsorption and reaction) method. X-ray diffraction study confirms the formation of nanocrystalline cubic phase of cadmium oxide in the films. Lattice constant is determined using Nelson Riley plots. Using X-ray broadening, crystallite sizes, lattice strain, stress and energy density were studied by using Williamson-Hall method and modified Williamson-Hall method. From literature review, it is seen that a number of researchers have applied these two methods for structural characterization of thin films of different nanocrystals, but till now modified Williamson-Hall method has not been used for CdO nanocrystals. Hence, we have used these methods for structural characterization of deposited CdO thin films. The ultra-high resolution transmission electron microscopic (UHRTEM) study shows that the shape of the particles is nearly spherical and the average particle size agrees well with the result obtained from X-ray diffraction study. Selected area electron diffraction patterns have also supported the formation of cubic phase of cadmium oxide.
关键词： Nelson-Riley plot,Cadmium oxide thin films,Williamson-Hall plot,Size-strain plot
更新于2025-09-23 15:21:01
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Drying-induced soil shrinkage and desiccation cracking monitoring with distributed optical fiber sensing technique
摘要： Monitoring of drying-induced volume shrinkage and desiccation cracking in clayey soils is of great importance in geological and geotechnical engineering. Compared with conventional strain monitoring methods providing discrete measurements, the Brilliouin optical time domain reflectometer (BOTDR) technique enables continuous measurement of the distributed strain generated along optical fibers. In this study, a physical model test is conducted to investigate the feasibility of monitoring drying-induced soil shrinkage and desiccation cracking using BOTDR. Three optical fibers with different surface protections (thermoplastic polyester elastomer (TPEE) jacket, nylon jacket, and acrylate coating) are tested and compared. Experimental results validate that BOTDR is applicable for the direct strain monitoring of desiccation cracking soils. Monitored strain values are strongly influenced by water content, soil cracking, and fiber types. The strain measured by the optical fiber reaches only several micro strains when the soil is over-saturated, gradually increases with the decreasing water content and the increasing soil-fiber interfacial shear stresses, and drops rapidly after the occurrence of decoupling between fiber and soil resulting from the mature development of desiccation cracks. The optical fiber with acrylate coating is not suitable because of its fragility and the poor interfacial coupling with the soil. Optical fibers covered with TPEE jacket or nylon jacket are both applicable for soil strain monitoring, with the former one more sensitive to water content variations. The study is the first attempt to apply the BOTDR technique for the direct and continuous monitoring of drying-induced soil shrinkage and desiccation cracking process. It is expected bring new insights into the fundamental understanding of volumetric shrinkage and desiccation cracking in clayey soils.
关键词： Brilliouin optical time domain reflectometer (BOTDR),Desiccation crack,Volumetric shrinkage,Strain monitoring,Optical fiber sensing
更新于2025-09-23 15:21:01
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Interfacial strain and shell thickness effect on core squeeze/stretch in core/shell quantum dots
摘要： Large surface to volume ratio in zero dimension core/shell quantum dots makes lattice mismatch induced interfacial strain vital in determining structural and optical properties of nanostructures. In this study, changes in lattice mismatch induced strain from different compressive shell (CdS–ZnS) with different thicknesses (thin and thick) are evaluated and its effect on capped core diameter is theoretically calculated. Capped core squeeze amount is compared with its initial (bare) diameter obtained from transmission electron microscopy. The capped core diameter is first calculated theoretically using effective mass approximation. Then, same diameter is obtained from modified version of effective mass approximation method that considers interfacial strain amount. Comparison of the results with bare core size obtained from transmission electron microscopy revealed effect of shell thickness imposed on capped core diameter. Results show, larger lattice mismatch between core and shell induces higher strain amount on the core thereby larger squeezes the core. At the meantime, it is shown that, thicker compressive shell enforces lower stress on core as it widens its distance from core due to lattice relaxation. Hence, core is squeezes less under thicker shell.
关键词： Capped core size,Shell thickness,Interfacial strain
更新于2025-09-23 15:21:01
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AlInGaN-based superlattice p-region for improvement of performance of deep UV LEDs
摘要： A deep ultraviolet light-emitting diode (DUV LED) consisting of a specifically designed intermediate p-type region involving a superlattice quaternary nitride alloy has been proposed. The light output power of the proposed structure has been found significantly large; around 28.30 times high in comparison to the conventional structure, at the current density of 200 A/cm2. The maximum internal quantum efficiency of the proposed structure is 153.63% higher compared to the conventional one. Moreover, the efficiency droop has been reduced by 99.08%. Absence of abrupt potential barrier owing to the strain compensation provided by the superlattice p-AlInGaN layer offers an attractive solution for enhancing the hole injection into the active region leading to the improvement in performance of DUV LED.
关键词： Efficiency droop,Superlattice-AlInGaN,Strain compensation,DUV LED
更新于2025-09-23 15:21:01