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Near-ultraviolet Raman and micro-Raman analysis of electronic materials
摘要： Raman and micro-Raman analysis methods have been extensively investigated for the study of materials used in electronic and photonic devices. Raman studies are used to understand fundamental phonon properties, along with effects related to the crystal structure, disorder, doping, and external factors such as temperature and stress. Micro-Raman extends these investigations to the micron scale. This article reviews diverse benefits of Raman measurements when carried out using laser excitation in the near-ultraviolet wavelength range, nominally 400 to 325 nm. Micro-Raman methods in the near ultraviolet exploit the key advantage of reduced focal spot size, achievable at shorter wavelengths when using diffraction-limited optics, for mapping with high spatial resolution. There are distinct advantages common to Raman and micro-Raman spectroscopy in the near ultraviolet when compared to the widely used visible excitation. One advantage exploits the shallower optical penetration depth in select materials for probing near-surface regions or interfaces. A second advantage is related to tuning of the excitation photon energy relative to the electronic levels of a material for investigating resonance effects. Finally, the application of Raman scattering to materials which exhibit strong fluorescence requires tuning to a wavelength range away from the potentially obscuring emission. This article overviews several examples of these key advantages to study diverse applied physics problems in electronic and photonic materials. Topics covered include stress mapping in silicon and related materials, stress and thermal effects in gallium nitride and other group-III-nitride semiconductors, and carbon materials ranging from graphite and graphene to diamond grown using chemical vapor deposition. The fundamental effects of stress- and temperature-induced shifts in phonon energies and their application to study epitaxy and device-related effects are also briefly reviewed.
关键词： near-ultraviolet,stress mapping,carbon materials,chemical vapor deposition,phonon properties,Raman spectroscopy,electronic materials,micro-Raman,gallium nitride
更新于2025-09-23 15:21:01
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Thermal properties and remnant state variables of ferroelectric ceramics switched by both electric field and compressive stress at room temperature
摘要： A commercial poled ferroelectric cube specimen is subject to electric ?eld and compressive stress of various magnitudes at the reference temperature 20 °C. After reaching speci?c states of remnant polarization and remnant strains, temperature of the specimen increases under no external load, measuring changes in polarization and strains. Assuming constant values of thermal properties in the temperature range of interest, we estimated pyroelectric and thermal expansion coe?cients for all tested levels of electric and stress ?elds and plotted them versus remnant state variables at 20, 50, 80, and 110 °C. The distributions of thermal properties ?t well into quadratic curves independent of electric and stress ?elds at each of the four temperatures. One could predict successfully the quadratic ?tting curves at high temperatures by using the equations of quadratic ?tting curves at reference temperature. Remnant state variables also seem to have close correlation among themselves, independent of the levels of applied electric ?eld or stress. ? 2018 The Japan Society of Applied Physics
关键词： thermal properties,compressive stress,electric ?eld,ferroelectric ceramics,remnant state variables
更新于2025-09-23 15:21:01
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[Laser Institute of America ICALEO? 2015: 34th International Congress on Laser Materials Processing, Laser Microprocessing and Nanomanufacturing - Atlanta, Georgia, USA (October 18–22, 2015)] International Congress on Applications of Lasers & Electro-Optics - Microstructural effects induced by laser shock peening for mitigation of stress corrosion cracking
摘要： Stress corrosion cracking is a phenomenon that can lead to rapid, sudden failure of metallic products. In this paper we examine the mechanisms of SCC mitigation of stainless steel and brass samples using laser shock peening (LSP). The behavior of hydrogen within the crystal lattice is one of the most dominant contributors to SCC, where uptake of hydrogen strains the lattice and increases its hardness. Cathodic charging of the metallic samples in 1M sulfuric acid was performed in order to accelerate hydrogen uptake. Non-treated samples underwent hardness increases of 28%, but LSP treated samples only increased in the range of 0 to 8%, indicative that LSP keeps hydrogen from permeating into the metal. Mechanical U-bends subjected and MgCl2 environments are analyzed, to determine changes in fracture morphology. Surface chemical effects are addressed via Kelvin Probe Force Microscopy, which is used for finding changes in the work function caused by LSP treatment. A finite element model of material deformation from U-bending was developed to analyze and compare the induced stresses. With LSP, there is a potential for overprocessing the samples, whereby negative effects refinement, to corrosion martensite formation) can arise. Detection of any martensite phases formed is performed using x-ray diffraction. We find LSP to be beneficial for stainless steel but does not improve brass’s SCC resistance. With our analysis methods we provide a further understanding of the process whereby LSP reduces subsequently highlight SCC for important implementation of the process.
关键词： Brass,Stainless steel,Hydrogen uptake,Stress corrosion cracking,Cathodic charging,Kelvin Probe Force Microscopy,Laser shock peening,Finite element model
更新于2025-09-23 15:21:01
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Bayesian Spectroscopy on Polarization Dependent Photoluminescence Spectra of Doubly-Split Excitons in a Cu <sub/>2</sub> O Thin-Crystal Sandwiched by MgO Substrates
摘要： By using Bayesian spectroscopy, we studied polarization dependence of photoluminescence (PL) spectra in doubly-split 1S yellow ortho-excitons in a Cu2O thin-crystal recrystallized in a small gap between paired MgO substrates. In these thin-crystals, biaxial stresses are expected to be involved due to a small lattice mismatch between Cu2O and MgO. Under a planar-isotropic biaxial stress, the cubic symmetry degrades to the tetragonal one in Cu2O, and subsequently, the ortho-exciton state splits into two states having different symmetries. Consequently, the resonant PL intensities of the doubly-split ortho-excitons are expected to show different polarization dependencies. To elucidate such biaxial stress effect, we measured polarization dependence of the PL spectra at 4.2 K. Although resonant weak PL bands of the doubly-split exciton states and their intense phonon sidebands co-exist, we succeeded in decomposing to the respective spectral components by the Bayesian spectroscopy with a replica exchange Monte Carlo algorithm. As a result, it is found that the resonant PL band appearing on higher energy side shows hardly polarization dependence, whereas the resonant PL band appearing on lower energy side is further weak and shows noticeable polarization dependence. These results can be explained by the selection rule and polarization dependences on the transition matrix elements of quadrupole transitions of the doubly-split ortho-exciton states, and it clearly shows that the crystal symmetry degrades to D4h by the isotropic biaxial stress involved in the Cu2O thin-crystals.
关键词： Bayesian spectroscopy,excitons,biaxial stress effect,polarization dependence,Cu2O
更新于2025-09-23 15:21:01
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Crack behavior in ultrafast laser drilling of thermal barrier coated nickel superalloy
摘要： Quantitative analysis is required to explore the mechanism of crack generation in ultrafast laser drilling of thermal barrier coated nickel superalloy. In this study, a simple thermo-mechanical coupled model is established to obtain temperature history, phase transformation stress and thermal stress during drilling process, in which laser beam scanning, laser intensity attenuation, the nonlinear relationship between drilling depth and drilling time are involved. The induced stress obtained from the present model is compared with the results by digital image correlation (DIC) method. According to the crack distribution around the drilled hole, the present model is used to explain the mechanism of crack behavior in drilling of multilayer materials. Finally, the strategy using low pulse repetition rate or water jet assisted method is suggested to reduce the thermal effect in ultrafast laser drilling process.
关键词： TBC,Phase transformation stress,Thermal stress,Crack behavior,Ultrafast laser,Laser drilling
更新于2025-09-23 15:19:57
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Research on a new laser path of laser shock process
摘要： In most laser shock process experiments, the traditional typical laser path is usually in use. However, the surface residual stress induced by laser shock process distribute unbalance. The residual stress released from the minimum axis, the effective of the laser shock process would lose. To solve it, a new laser path produced, the horizontal and vertical reciprocating (HVR). With the new path, the residual stress distribution unbalance reduced. The laser shock process efficiency improved. The traditional laser path induced stress unbalance produced by the time different between the laser pulse and stress pulse. The stress would overlay to the direction of the laser path, it’s the main reason that the material surface stress distribution unbalance. The laser pulse is 12-20ns for most cases, but the stress pulse is 3 times of it. The results of the simulation shows the traditional laser path X axis stress is 25% larger than the Y axis, but the HVR path is nearly the same. The experiments of the results not only show the two laser path stress distribution different but also the laser shock area different affect the stress distribution. The laser path different affect stress distribution unbalance reason is because the overlay, and the laser shock area affect stress distribution different reason is the resilience.
关键词： laser shock process,laser path,HVR path,residual stress,stress distribution
更新于2025-09-23 15:19:57
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Silicon solar cell-integrated stress and temperature sensors for photovoltaic modules
摘要： We propose silicon solar cell–integrated stress and temperature sensors as a new approach for the stress and temperature measurement in photovoltaic (PV) modules. The solar cell–integrated sensors enable a direct and continuous in situ measurement of mechanical stress and temperature of solar cells within PV modules. In this work, we present a proof of concept for stress and temperature sensors on a silicon solar cell wafer. Both sensors were tested in a conventional PV module setup. For the stress sensor, a sensitivity of (?47.41 ± 0.14)%/GPa has been reached, and for the temperature sensor, a sensitivity of (3.557 ± 0.008) × 10?3 K?1 has been reached. These sensors can already be used in research for increased measurement accuracy of the temperature and the mechanical stress in PV modules because of the implementation at the precise location of the solar cells within a laminate stack, for process evaluation, in-situ measurements in reliability tests, and the correlation with real exposure to climates.
关键词： in situ measurement,temperature measurement,PV module,temperature sensor,stress sensor,stress measurement,predictive maintenance
更新于2025-09-23 15:19:57
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Effect of numerical aperture on molten area characteristics in micro-joining of glass by picosecond pulsed laser
摘要： Glass products with precise and sophisticated shapes are highly demanded in the field of MEMS due to their excellent properties. Ultrashort pulsed laser has been expected to be a powerful and reliable tool for micro-welding of glass. Focusing condition such as numerical aperture (N.A.) is a critical parameter that controls how ultrashort laser pulses interact with and propagate in glass, and it has a great influence on the laser micro-welding characteristics of glass. In order to investigate the quality of welding process, it is important to understand the dependence of the mechanical strength of molten area created in glass specimen with various numerical apertures. Therefore, the mechanical strength of molten area with various numerical apertures was evaluated in micro-welding of glass by picosecond pulsed laser. Higher bending strength could be obtained under an appropriate volume ratio of molten area and glass specimen, when continuous molten areas were formed. In addition, high density and large size of molten area without crack led to higher breaking stress. It is concluded that superior focusing characteristics such as N.A. 0.65 enable a long region of high power density in beam axis, which can satisfy both high mechanical strength and high processing speed.
关键词： Picosecond pulsed laser,Breaking stress,Bending strength,Glass material,Numerical aperture
更新于2025-09-23 15:19:57
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Numerical studies of residual states and scaling effects in laser-directed energy deposition additive manufacturing
摘要： Sequentially coupled thermo-mechanical model was used to simulate the residual stresses and residual distortions in the directed energy deposition additive manufacturing by laser. The proposed models were validated by comparison with experimental data. Different sizes of components were used to study the scaling effects. Results indicate that the residual stress can be controlled by the component sizes. This phenomenon can be explained by the bending deformation and the temperature fluctuations, especially the cooling rate, in the directed energy deposition additive manufacturing process. Both the bending deformation and the temperature fluctuations can be controlled by the ambient temperature and the designed process parameters. Analytical model was established to show how the components’ sizes affect the final residual states in combination with different design parameters.
关键词： Scaling effect,Residual stress,Residual distortion,Additive manufacturing
更新于2025-09-23 15:19:57
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Experimental and Numerical Simulation on Laser welding of High Manganese TWIP980 Steel
摘要： In this paper, the numerical simulation of laser tailoring process for the 2mm thickness TWIP980 steel sheet is carried out using Simufact welding software. The results show that the center of the laser welding heat source is small, and temperature is high. The front of the weld pool has a drop-shaped profile and a funnel-shaped cross section. The simulated weld joint has a high degree of conformity comparing to the actual weld joint. As the heat input (line energy) increases, the peak temperature of the thermal cycle and the weldment width increase. The simulated results indicate that the residual stress of the weld joint perpendicular to the weld along the surface is greater than that along the weld direction, and are both greater than the residual stress perpendicular to the weld along the thickness direction. The residual stress generated by welding is mainly concentrated in the direction perpendicular to the weld seam. With the heat input increase, the deformation after welding increases. For the studied TWIP980 steel, the recommending laser tailored blank (LTB) weld parameters are: power 3kW and welding speed 3m/min, which is the optimum welding process in the practical welding. The guiding significance of the software for laser welding simulation of TWIP980 steel was verified.
关键词： numerical simulation,laser welding,residual stress,temperature field,TWIP980 steel
更新于2025-09-23 15:19:57