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Formation of ordered defect structures in lithium niobate crystals of different chemical composition at non-equilibrium processes of different nature
摘要： Ordered defective structures in lithium niobate crystals have been established. The phenomenon is a result of non-equilibrium processes of a different nature: photo-induced light scattering, laser ablation, and creation of cracks during relieving mechanical stresses. The shape of such structures depends on the nature and energy that affect a crystal. A number of concentric areas with a different density of laser-induced defects with a changed refractive index appear during photoinduced light scattering. Concentric clusters of microdomains appear in a macrodomain of another sign at laser ablation as a result of local switching under impulse laser radiation. A number of microcracks with a fractal structure appear near main macro-crack during cracking under mechanical stress. Thus, appearance of ordered defective structure occurs not only in the local spot of direct exposure to laser radiation, mechanical stress, etc., but also in some volume of a crystal around it.
关键词： Doping,Laser ablation,Lithium niobate,Mechanical stress,Defective structure,Photorefractive effect
更新于2025-11-21 11:24:58
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Effect of Macro-scale Mechanical Stress of Silicon Wafer on Room Temperature Photoluminescence Signals
摘要： Mechanical stress was applied to single side polished and double side polished Si wafers in polypropylene wafer containers for different localized stress levels and durations. Room temperature photoluminescence (RTPL) spectra from Si wafers were measured before and after applying localized mechanical stress. Significant changes (up to 26% increase) in RTPL intensity were measured from areas under different stress levels even 1 year after the fixtures for mechanical stress generation were removed. Significant effects of localized mechanical stress on RTPL intensity variations were measured up to 49 days after the fixture removal. Nearly fully relaxed RTPL signatures for localized mechanical stress were measured 450 days after the fixture removal. RTPL intensity is found to be very sensitive to the externally applied macro-scale mechanical stress of Si wafers and residual (or memorized) internal stress even after removal of fixtures for external mechanical stress generation.
关键词： Silicon,room temperature photoluminescence,stress relaxation,mechanical stress
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE International Ultrasonics Symposium (IUS) - Kobe, Japan (2018.10.22-2018.10.25)] 2018 IEEE International Ultrasonics Symposium (IUS) - Accelerated Aging Procedures of Bending Piezoelectric Structures Using Electrical Stress Induced Approaches
摘要： Efficient AgInGaS quantum dot-based energy harvesting devices using electrical and mechanical approaches
关键词： energy harvesting,quantum dots,optoelectronics,AgInGaS,mechanical stress
更新于2025-09-23 15:22:29
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Evaluation of stress on metal surfaces by laser-induced breakdown spectroscopy
摘要： In this study, we evaluated the feasibility of using laser-induced breakdown spectroscopy (LIBS) to determine the stress generated in metal materials by comparing measured stress levels with those determined by x-ray diffraction (XRD). Magnesium (Mg) alloy specimens underwent impact stress generated under ultrasonic peening. Stainless steel specimens were subjected to bending stress. The reference stress for each specimen was measured using XRD. LIBS measurements were performed to determine the correlation between stress distribution and the ratio of ionic to atomic spectral line intensity. The stress distribution from the surface to the interior of the ultrasonic-peened specimens measured by LIBS showed a similar tendency to that measured by XRD, but there was a difference in the maximum measurable depth. Additionally, the tensile and compressive stress distributions measured by LIBS on bending specimens showed similar trends to those of XRD. From these results, it was possible to measure the correlation between the stress state of the metal matrix and the spectral line strength of LIBS, thus confirming the potential for stress measurement using LIBS.
关键词： laser-induced breakdown spectroscopy,mechanical stress,spectral line
更新于2025-09-23 15:19:57
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Development of a Flexible Tunable and Compact Microstrip Antenna via Laser Assisted Patterning of Copper Film
摘要： Design and rapid prototyping of a tunable and compact industrial, scientific and medical (ISM) band microstrip antenna for applications is presented in this paper. Laser machining is introduced as a fast and accurate method for the antenna fabrication. The antenna, with an overall dimension of 65 × 46 × 0.127 mm, was fabricated by sandwiching a flexible Kapton polyimide substrate, with a dielectric constant of 3.5, between two flexible copper tapes, as the radiating patch and ground plane, respectively. The radiating patch was patterned in a meander configuration, with three slots, demonstrating the capability to reduce the resonant frequency of the microstrip antenna from 2.4 GHz to 900 MHz, without increasing the overall size of the antenna (87% compact). The effect of mechanical stress on the antenna performance was investigated by performing bend and stretch tests. The antenna was subjected to compressive bend with a minimum radius of curvature of 86 mm and 150 mm along the x- axis and y- axis which resulted in a maximum increase of resonant frequency by 3.1% and 1.3%, respectively. Similarly, the antenna was subjected to tensile bend with a minimum radius of curvature of 79 mm and 162 mm along the x- axis and y- axis which resulted in a maximum decrease of the resonant frequency by 4.2% and 0.3%, respectively. An overall 0.9% decrease in the resonant frequency was measured for an applied strain of 0.09% during stretching the antenna along the y- axis.
关键词： mechanical stress,flexible Kapton substrate,Compact tunable antenna,microstrip patch antenna,laser machining
更新于2025-09-23 15:19:57
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Mechanical stress dependence of the Fermi level pinning on an oxidized silicon surface
摘要： A combination of micro-Raman spectroscopy and micro-XPS (X-ray photo-electron spectroscopy) mapping on statically deflected p-type silicon cantilevers is used to study the mechanical stress dependence of the Fermi level pinning at an oxidized silicon (001) surface. With uniaxial compressive and tensile stress applied parallel to the ?110? crystal direction, the observations are relevant to the electronic properties of strain-silicon nano-devices with large surface-to-volume ratios such as nanowires and nanomembranes. The surface Fermi level pinning is found to be even in applied stress, a fact that may be related to the symmetry of the Pb0 silicon/oxide interface defects. For stresses up to 240 MPa, an increase in the pinning energy of 0.16 meV/MPa is observed for compressive stress, while for tensile stress it increases by 0.11 meV/MPa. Using the bulk, valence band deformation potentials the reduction in surface band bending in compression (0.09 meV/MPa) and in tension (0.13 meV/MPa) can be estimated.
关键词： Mechanical stress,Raman spectroscopy,X-ray photoelectron spectroscopy,Surface Fermi level pinning,Silicon,Interface defect
更新于2025-09-19 17:15:36
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Tensile control of the thermal flow in plasmonic heaters realized on flexible substrates
摘要： In this paper, we present a simple and robust numerical method capable of predicting, with high accuracy, the thermal effects occurring for different gold nanoparticle arrangements under externally applied strain. The physical system is numerically implemented in the COMSOL Multiphysics simulation platform. The photothermal response of different arrangements of gold nanoparticles, resonantly excited by linearly polarized light, is considered with the system at rest and under the action of mechanical stress. The generation of heat at the nanoscale is analyzed by considering how this is affected by the variation of the extinction cross section. We describe the peculiar conditions under which mechanically controlled gold nanoparticle arrangements can significantly increase the local temperature due to the formation of localized photothermal hot spots. The resulting systems are envisioned in applications as optomechanically tunable plasmonic heaters.
关键词： COMSOL Multiphysics,photothermal effects,mechanical stress,plasmonic heaters,gold nanoparticles
更新于2025-09-12 10:27:22
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Extent of embossing-related residual stress on the magnetic properties evaluated using neutron grating interferometry and single sheet test
摘要： Due to the permanently increasing maximum speed of modern electric machines, the mechanical load on the electrical steel rises. The punched flux barriers of reluctance machines play an increasingly key role in the mechanical design. The weakening of the material and the notching effect can cause local failure due to centrifugal force. In this paper, a method is presented which induces residual stresses by embossing electrical steel laminations, which contribute to the guidance of the magnetic flux and cause a negligible mechanical weakening of the sheet. The aim of this paper is to demonstrate the effectiveness of these embossed flux barriers. This is achieved by using neutron grating interferometry, that allows the density of the magnetic domains to be resolved locally. Furthermore the influence of the embossing is mapped globally by single sheet tests. The finite element analysis of the forming process derives the residual stress distribution which is responsible for the measured magnetic behavior. In order to isolate the influence of the residual stress, non-embossed and stress-relief annealed specimens are used as a reference for both measurement methods.
关键词： Electrical steel,Forming,Electric drives,Neutron grating,Production,Single sheet tester,Mechanical stress,Embossing
更新于2025-09-04 15:30:14