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Strain Mapping of CdTe Grains in Photovoltaic Devices
摘要： Strain within grains and at grain boundaries (GBs) in polycrystalline thin-film absorber layers limits the overall performance because of higher defect concentrations and band fluctuations. However, the nanoscale strain distribution in operational devices is not easily accessible using standard methods. X-ray nanodiffraction offers the unique possibility to evaluate the strain or lattice spacing at nanoscale resolution. Furthermore, the combination of nanodiffraction with additional techniques in the framework of multimodal scanning X-ray microscopy enables the direct correlation of the strain with material and device parameters such as the elemental distribution or local performance. This approach is applied for the investigation of the strain distribution in CdTe grains in fully operational photovoltaic solar cells. It is found that the lattice spacing in the (111) direction remains fairly constant in the grain cores but systematically decreases at the GBs. The lower strain at GBs is accompanied by an increase of the total tilt. These observations are both compatible with the inhomogeneous incorporation of smaller atoms into the lattice, and local stress induced by neighboring grains.
关键词： X-ray microscopy,nanodiffraction,X-ray diffraction (XRD),solar cells,multimodal,CdTe,X-ray,strain,X-ray fluorescence (XRF),photovoltaic,X-ray beam induced current (XBIC)
更新于2025-09-19 17:13:59
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Effect of Nd:YAG pulsed laser welding process on the liquation and strain-age cracking in GTD-111 superalloy
摘要： The weldability of GTD-111 nickel-based superalloy by Nd:YAG pulse laser with an average power of 250 W was studied using several pre- and post-weld heat treatment cycle, and the characteristics of liquation, solidification and strain-age cracks were also investigated. The results revealed that liquation cracks in the GTD-111 Nickel-Based Cast Superalloy were associated with the constitutional liquation of γ′ particle, MC carbides, inter-dendritic γ-γ? eutectic and melting of Cr-rich boride. Also, cracking during welding occurred at the places that the concentration of Al and Ti is high. Crack-free laser welds were observed in the MT1 conditions (1200 ℃ for 2 h) owing to dissolution of deleterious phases before welding. γ′ phase had little effect on the incidence of cracking in the MT1 condition. An analysis of the microstructures indicated that the cracking was caused primarily by liquation in the as-welded condition and was exacerbated by post-weld heat treatment cracking during the subsequent heat treatment. aging heat treatment of samples which were undergone aging heat treatment before welding, resulted in the formation of strain-age cracking due to γ? and γ-γ? eutectic phases precipitation. The results of micro-hardness indicated that the hardness of fusion zone (FZ) was higher than that of HAZ and base metal zone (BMZ). The liquation cracking in the heat affected zone (HAZ) was observed to be affected by the hardness of base-alloy.
关键词： Laser beam welding,GTD-111 superalloy,Liquation cracking,Strain age cracking
更新于2025-09-19 17:13:59
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Visualization of subnanometric phonon modes in a plasmonic nano-cavity via ambient tip-enhanced Raman spectroscopy
摘要： Phonons provide information on the physicochemical properties of a crystalline lattice from the material’s vibrational spectrum. Optical phonons, in particular, can be probed at both micrometre and nanometre scales using light-based techniques, such as, micro-Raman and tip-enhanced Raman spectroscopy (TERS), respectively. Selection rules, however, govern the accessibility of the phonons and, hence, the information that can be extracted about the sample. Herein, we simultaneously observe both allowed and forbidden optical phonon modes of defect-free areas in monolayer graphene to study nanometre scale strain variations and plasmonic activation of the Raman peaks, respectively, using our home-built TERS system in ambient. Through TERS imaging, strain variations and nanometre-sized domains down to 5 nm were visualised with a spatial resolution of 0.7 nm. Moreover, such subnanometric con?nement was found to activate not only the D and D’ forbidden phonon modes but also their D + D’ combination mode. With our TERS in ambient system, the full phonon characterisation of defect-free graphene and other 2D nanomaterials is now possible, which will be useful for subnanometre strain analysis and exploring the inherent properties of defect-free materials.
关键词： graphene,plasmonic nano-cavity,tip-enhanced Raman spectroscopy,phonon modes,strain analysis
更新于2025-09-19 17:13:59
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Strain-induced structural phase transition, electric polarization and unusual electric properties in photovoltaic materials CsMI <sub/>3</sub> (M = Pb, Sn)
摘要： The structural phase transition, ferroelectric polarization, and electric properties have been investigated for photovoltaic films CsMI3 (M = Pb, Sn) epitaxially grown along (001) direction based on the density functional theory. The calculated results indicate that the phase diagrams of two epitaxial CsPbI3 and CsSnI3 films are almost identical, except critical transition strains varying slightly. The epitaxial tensile strains induce two ferroelectric phases Pmc21, and Pmn21, while the compressive strains drive two paraelectric phases P212121, P21212. The larger compressive strain enhances the ferroelectric instability in these two films, eventually rendering them another ferroelectric state Pc. Whether CsPbI3 or CsSnI3, the total polarization of Pmn21 phase comes from the main contribution of B-position cations (Pb or Sn), whereas, for Pmc21 phase, the main contributor is the I ion. Moreover, the epitaxial strain effects on antiferrodistortive vector, polarization and band gap of CsMI3 (M = Pb, Sn) are further discussed. Unusual electronic properties under epitaxial strains are also revealed and interpreted.
关键词： structural phase transition,electric properties,photovoltaic films,ferroelectric polarization,epitaxial strain,density functional theory,CsMI3
更新于2025-09-19 17:13:59
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Strain in InP/ZnSe, S core/shell quantum dots from lattice mismatch and shell thickness—Material stiffness influence
摘要： We investigate the buildup of strain in InP quantum dots with the addition of shells of the lower-lattice constant materials ZnSe and ZnS by Raman spectroscopy. Both materials induce compressive strain in the core, which increases with increasing shell volume. We observe a difference in the shell behavior between the two materials: the thickness-dependence points toward an influence of the material stiffness. ZnS has a larger Young’s modulus and requires less material to develop stress on the InP lattice at the interface, while ZnSe requires several layers to form a stress-inducing lattice at the interface. This hints at the material stiffness being an additional parameter of relevance for designing strained core/shell quantum dots.
关键词： Raman spectroscopy,ZnSe,ZnS,strain,material stiffness,InP quantum dots
更新于2025-09-19 17:13:59
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Strain tunable quantum dot based non-classical photon sources
摘要： Semiconductor quantum dots are leading candidates for the on-demand generation of single photons and entangled photon pairs. High photon quality and indistinguishability of photons from different sources are critical for quantum information applications. The inability to grow perfectly identical quantum dots with ideal optical properties necessitates the application of post-growth tuning techniques via e.g. temperature, electric, magnetic or strain fields. In this review, we summarize the state-of-the-art and highlight the advantages of strain tunable non-classical photon sources based on epitaxial quantum dots. Using piezoelectric crystals like PMN-PT, the wavelength of single photons and entangled photon pairs emitted by InGaAs/GaAs quantum dots can be tuned reversibly. Combining with quantum light-emitting diodes simultaneously allows for electrical triggering and the tuning of wavelength or exciton fine structure. Emission from light hole exciton can be tuned, and quantum dot containing nanostructure such as nanowires have been piezo-integrated. To ensure the indistinguishability of photons from distant emitters, the wavelength drift caused by piezo creep can be compensated by frequency feedback, which is verified by two-photon interference with photons from two stabilized sources. Therefore, strain tuning proves to be a flexible and reliable tool for the development of scalable quantum dots-based non-classical photon sources.
关键词： quantum dot,on-chip,piezoelectric crystal,entangled photons,fine structure splitting,strain tuning
更新于2025-09-19 17:13:59
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Wrinkled titanium nitride nanocomposite for robust bendable electrodes
摘要： Electrical contacts and interconnections are critical components for all electronic devices. Bendable electrodes with enhanced electro-mechanical properties are highly desirable to develop innovative wearable electronic devices. Herein we report on a fabrication method for robust bendable coatings based on titanium nitride (TiN) thin films and silver nanowires (Ag NWs). TiN and TiN-AgNWs nanocomposites were deposited on polyethylene terephthalate (PET) substrates using a plasma enhanced pulsed laser deposition (PLD) technique. The resulting TiN coatings exhibit excellent adhesion to PET and their sheet resistance can be tuned using a dual frequency PLD process and further decreased by incorporating Ag NWs into the TiN layers. Sample sheet resistance was decreased down to values as low as 3.5 Ω/□, thanks to the formation of TiN-AgNWs nanocomposites. The electro-mechanical robustness of TiN based coatings were evaluated by four-probe resistance measurements in situ under cyclic bending tests. We show that the TiN-AgNWs nanocomposites surpass both ITO and Ag NWs coatings in terms of mechanical robustness and electrical conductivity respectively. These nanocomposites withstand high strain fatigue loading up to ε = 2.6%, keeping RS below 5 Ω/□. The data demonstrates that the incorporation of Ag NWs in TiN coatings improve the mechanical robustness, limiting the crack growth and propagation, with low optical transmittance decrease (≈11%). These results indicate that Ag NWs based nanocomposites are attractive materials for flexible electronic devices.
关键词： mechanical strain,titanium nitride,nanocomposite,ITO,flexible electrode,silver nanowires
更新于2025-09-19 17:13:59
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Size effect on optical performance of blue light-emitting diodes
摘要： In this paper, size effects on optical performance of blue light-emitting diodes (LEDs) are investigated. The essential physical mechanism is studied by fabricating LEDs with various sizes of the active area and testing optical characteristics. It is found that micro-LEDs have better light extracting efficiency and thermal dissipation compared with broad-area LEDs, which is likely due to the small ratio of perimeter and active area. Furthermore, micro-LEDs are more beneficial for displays due to the stable wavelength under the low pulse width modulation (PWM) current density.
关键词： size dependence,micro-LED,strain relaxation,light extract efficiency
更新于2025-09-19 17:13:59
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Strain Engineering Coupled with Optical Regulation towards High-sensitivity In2S3 Photodetector
摘要： Non-layered 2D materials possess intriguing properties, widening the scope of 2D libraries and promising considerable potential for applications in next-generation optoelectronics. However, due to the surface dangling bonds and weak light adsorption arising from atomically thin thickness, their photosensitivity is still limited. Herein, we achieve an ultrasensitive 2D In2S3 photodetector by adopting strain engineering coupled with optical regulation. A SiO2 nanograting array was introduced to construct strained morphology of 2D In2S3. This morphology induces charge localization and renders back-to-back built-in electric field array, which efficiently suppresses the dark current and separates the photo-excited carriers. Simultaneously, the SiO2 nanograting array realizes light management and improves the light harvesting. As a result, the device presents an ultralow dark current of 3.2 pA with a high signal-to-noise ratio up to 1.7 × 106. Especially, a prominent photoresponsivity of 1810 A/W, an excellent detectivity of 2.09 × 1015 Jones and a fast response speed of 0.41 ms are achieved. This work depicts an effective scheme to associate photonic/electronic properties manipulation for optoelectronic applications.
关键词： strain engineering,SiO2 nanograting,In2S3,optical regulation,photodetector,2D materials
更新于2025-09-19 17:13:59
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High-speed infrared imaging and mesostructural analysis of localized temperature rise in damage and failure behavior of 3-D braided carbon/epoxy composite subjected to high strain-rate compression
摘要： This investigation is aimed to study the dynamic failure behavior of 3-D braided carbon/epoxy composite by capturing the high-speed infrared image and simulating the temperature-rise response under high strain-rate compression. It is found that localized temperature rise is a good indication in damage and failure of the 3-D braided composite. Localized temperature can rise above a hundred degrees Celsius, reaching or even exceeding the Tg of the matrix resin and imperiling the polymer along damage regions in specimen. Temperature rise in localized paths of the specimens was caused by adiabatic shear along the boundaries of braided fibers or inside the fiber bundles. Sustaining decrease in stress after the peak strength is related to shear deformation, temperature rise and progressive damage. There is a correlation among localization of temperature rise, adiabatic shear band, resin softening, damages and failures in the 3-D braided carbon/epoxy composite under dynamic compression loading. For the out-of-plane compression, temperature always conducts from the broken interface to the inside of the fiber bundles along the radial, which will lead to the weakening of resin in fiber bundles. And damages, penetrating cracks and openings are verified with ‘X’-shape localization of temperature rise. With the increase of strain rate, localization of temperature rise indicates that adiabatic shear bands begin to connect together to form larger and longer paths by the mutual shear effect among adjacent fiber bundles. For the in-plane compression, multi-cracks are found by observing the independent ‘zigzag’ shear bands converting to dependent ‘zigzag’ network. The temperature is easily localized at the crimp position of fiber bundle when they forming the ‘zigzag’ localization along the braiding paths of fiber bundles. However, some regions in 3-D braided carbon/epoxy composite have not experienced plastic shear deformation, which are isolated among ‘zigzag’ adiabatic shear network and their boundaries are the very paths for localized temperature rise.
关键词： High strain-rate compression,Braided composite,Adiabatic temperature rise,Thermomechanical failure
更新于2025-09-19 17:13:59