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Diluted nitride type-II superlattices: Overcoming the difficulties of bulk GaAsSbN in solar cells
摘要： We demonstrate type-II GaAsSb/GaAsN superlattices (SL) as a suitable structure to form the lattice-matched 1.0–1.15 eV subcell that would allow the implementation of the optimum monolithic multi-junction solar cell design. The separation of Sb and N atoms during growth leads to an improved composition homogeneity and a lower defect density than in the bulk GaAsSbN counterparts. The type-II band alignment SLs provide long radiative lifetimes that facilitate carrier collection as compared to equivalent type-I SLs. Moreover, the radiative lifetime can be controllably tuned through the period thickness, which is not possible in type-I SLs. A reduced period thickness results in enhanced absorption due to increased wavefunction overlap, as well as in a change in the transport regime from diffusive to quasiballistic, providing improved carrier extraction efficiency. As a result, the short period SL single-junction solar cells show an enhanced power conversion efficiency of 134% over the equivalent bulk devices.
关键词： Strain-balanced,GaAsSbN,Type-II band Alignment,Multi-junction solar cells,Superlattices,1 eV bandgap
更新于2025-09-23 15:19:57
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Mechanical response of a Laser Cladding repaired structure: localization of plastic strain due to microstructure gradient
摘要： Laser Cladding is an additive manufacturing technology enabling to repair complex metallic components by removing the worn region and reconstructing locally the initial geometry. The aim of this work is to study the mechanical response of Inconel 718 repaired thin walls. More precisely, we perform an EBSD imaging and in-situ SEM tensile tests on specimen whose gauge section contains the interface between base material and repaired area. We observe the multiaxial strain patterns until failure at the grain level using a Digital Image Correlation method and superpose this pattern with the microstructure gradient induced by repair. The observations highlight a strain localization phenomenon in repaired structures mainly due to grain size effect.
关键词： SEM tensile tests,Laser Cladding,Inconel 718,strain localization,EBSD,microstructure gradient,Digital Image Correlation
更新于2025-09-23 15:19:57
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Enhancement of the optical gain in GaAs nanocylinders for nanophotonic applications
摘要： Semiconductor nanolasers based on microdisks, photonic crystal cavities, and metallo-dielectric nanocavities have been studied during the last few decades for on-chip light source applications. However, practical realization of low threshold, room temperature semiconductor nanolasers is still a challenge due to the large surface-to-volume ratio of the nanostructures, which results in low optical gain and hence higher lasing threshold. Furthermore, the gain in nanostructures is an important parameter for designing all-dielectric metamaterial-based active applications. Here, we investigate the impact of p-type doping, compressive strain, and surface recombination on the gain spectrum and the spatial distribution of carriers in GaAs nanocylinders. Our analysis reveals that the lasing threshold can be lowered by choosing the right doping concentration in the active III–V material combined with compressive strain. This combination of strain and p-type doping shows 100× improvement in gain and approximately five times increase in modulation bandwidth for high-speed operation.
关键词： surface recombination,optical gain,compressive strain,GaAs nanocylinders,nanophotonic applications,p-type doping
更新于2025-09-23 15:19:57
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An investigation of aluminum nitride thin films patterned by femtosecond laser
摘要： In this study, a femtosecond laser etching method is proposed to pattern an aluminum nitride (AlN) ?lm, grown by metal-organic chemical vapor deposition on sapphire. Via control of typical pulse energies, the designed pattern was precisely written in the AlN ?lm. The morphology of the patterned structures was characterized using a three-dimensional laser scanning confocal microscope and a scanning electron microscope; crystalline quality and ?lm strain were analyzed using a Raman spectrometer and a transmission electron microscope. The results indicate that consistent morphologies were achieved with only slight changes to the crystalline quality. The tensile stress of the AlN ?lm was released, and the ?lm surface was slightly compressed after laser patterning. Thus, femtosecond etching has the potential to be an in situ patterning method during ?lm growth.
关键词： film strain,patterning,crystalline quality,femtosecond laser,aluminum nitride,thin films
更新于2025-09-23 15:19:57
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[Lecture Notes in Electrical Engineering] Sensors and Microsystems Volume 629 (Proceedings of the 20th AISEM 2019 National Conference) || Relative Humidity Sensor Based on Tip of Multimode Optical Fiber Integrated with Photonic Crystal of Hydrogel Coated Polystyrene Nanoparticles
摘要： A relative humidity (RH) sensing device based on photonic crystal colloids auto-assembled directly on the tip of a multi-mode optical fiber is here described. The core-shell nanospheres are obtained by Polystyrene (PS) nanoporous structures (core) incorporated into a poly(N-isopropylacrylamide) (PNIPAM) hydrogel (shell) and are subsequently deposited via a vertical dip-coating technique on a multimode optical fiber tip. The sensing capability is due to the hydrogel shell that swells depending on the relative humidity that induce wavelength shift and amplitude changes in the photonic bandgap peak. Spectral characterization and sensing analysis are performed, and the obtained results show that spectral characteristics are highly non-linear and strongly manufacturing dependent. A resolution of 1% RH is measured at 30% RH that significantly decreases at higher RH. Hereby, numerical simulations based on the finite element method (FEM) have been performed in order to investigate the sensing mechanism.
关键词： Structural health monitoring,Deflection monitoring,Optical fiber sensors,Strain measurement
更新于2025-09-23 15:19:57
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Photoelectric evaluation of dye-sensitized solar cells based on prodigiosin pigment derived from Serratia marcescens 11E
摘要： Prodigiosin, a natural pigment produced as a secondary metabolite by the non-photosynthetic bacterium Serratia marcescens, was tested as a sensitizer in dye-sensitized solar cells (DSSC). The strain S. marcescens 11E, which was isolated from a natural spring located in the northeastern Mexican state of Nuevo Leon, was cultivated on peanut oil broth 1% v/v, a culture medium which is known to enhance the production of prodigiosin. The resulting pigment was extracted with chloroform and identified as prodigiosin based on the spectroscopic and structural characteristics obtained by UV–Vis spectrophotometry along with FTIR and 1H-NMR spectroscopies. The initial absorbance decomposition test performed on the bacterial pigment demonstrated that prodigiosin exhibited high photostability after five days, while the photovoltaic performance test of the sensitized DSSC, resulted in an open voltage circuit of 560 mV, a current density of 0.096 mA/cm2, and efficiency of 0.032 %. Structurally, the DSSC consisted of a titanium dioxide (TiO2) photoanode sensitized with the pigment by direct adsorption, an electrolyte containing a redox pair I?/I3? and a cathode or counter electrode prepared from a carbon paste. Since the overproduction of prodigiosin can be easily achieved on a large scale through the rapid fermentation of agro-industrial residues throughout the year without the need to allocate surfaces for the cultivation of pigment-producing plants or wait for specific seasons for their cultivation, our results suggest that prodigiosin could be considered an excellent candidate to be used in the development of a low-tech, low-cost DSSC.
关键词： Low-cost DSSC,Solar energy,Bacterial pigments,Native strain
更新于2025-09-23 15:19:57
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[IEEE 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - Rome, Italy (2019.6.17-2019.6.20)] 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - Brillouin Optical Time Domain Analysis with Wavelength-locked Low-noise Pump-probe Laser Scheme
摘要： A doubly resonant short cavity Brillouin ring-laser actively stabilized with a wavelength locking system are employed as a low-RIN pump-probe source for Brillouin optical time-domain analysis (BOTDA) sensing. The developed high-stability narrow-linewidth laser scheme is compared to a long-cavity ring laser, showing the potential for enhanced temperature-strain resolutions.
关键词： wavelength-locked,temperature-strain resolutions,BOTDA,low-noise pump-probe laser,Brillouin Optical Time Domain Analysis
更新于2025-09-23 15:19:57
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Monitoring of Strain and Temperature in an Open Pit Using Brillouin Distributed Optical Fiber Sensors
摘要： Marble quarries are quite dangerous environments in which rock falls may occur. As many workers operate in these sites, it is necessary to deal with the matter of safety at work, checking and monitoring the stability conditions of the rock mass. In this paper, some results of an innovative analysis method are shown. It is based on the combination of Distributed Optical Fiber Sensors (DOFS), digital photogrammetry through Unmanned Aerial Vehicle (UAV), topographic, and geotechnical monitoring systems. Although DOFS are currently widely used for studying infrastructures, buildings and landslides, their use in rock marble quarries represents an element of peculiarity. The complex morphologies and the intense temperature range that characterize this environment make this application original. The selected test site is the Lorano open pit which is located in the Apuan Alps (Italy); here, a monitoring system consisting of extensometers, crackmeters, clinometers and a Robotic Total Station has been operating since 2012. From DOFS measurements, strain and temperature values were obtained and validated with displacement data from topographic and geotechnical instruments. These results may provide useful fundamental indications about the rock mass stability for the safety at work and the long-term planning of mining activities.
关键词： temperature,brillouin shift frequency,geotechnical monitoring system,strain,robotic total station,marble quarry,distributed optical fiber sensors,unmanned aerial vehicle
更新于2025-09-23 15:19:57
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Effect of Interface State Density of the AlGaN Electron Blocking Layer/GaN Barrier Layer in InGaN Blue Light-Emitting Diodes
摘要： Herein, two kinds of blue InGaN light-emitting diodes (LEDs) were compared in order to understand the effect of the strain originating from two different sapphire substrates. One of the LED types was grown on a patterned sapphire substrate (PSS), and the other was grown on a conventional sapphire substrate (CSS). The internal strains biased on InGaN quantum wells were compared by studying the time-resolved photoluminescence and the electroreflectance. Through analysis of the dynamic capacitance dispersion measurements, the relation between the trap states and trap density of the AlGaN electron blocking layer/GaN barrier interface above the InGaN quantum wells can be understood in great detail. The trapped charges of the CSSs have faster response times than those of the PSSs; this is attributed to the stronger piezo-field, which induces the AlGaN EBL/GaN barrier interface trap states to be effectively located at shallower levels from the conduction band.
关键词： Strain,Patterned sapphire substrate,InGaN quantum wells
更新于2025-09-23 15:19:57
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Concrete Crack Monitoring Using a Novel Strain Transfer Model for Distributed Fiber Optics Sensors
摘要： In this paper, we study the strain transfer mechanism between a host material and an optical fiber. A new analytical model handling imperfect bonding between layers is proposed. A general expression of the crack-induced strain transfer from fractured concrete material to optical fiber is established in the case of a multilayer system. This new strain transfer model is examined through performing wedge splitting tests on concrete specimens instrumented with embedded and surface-mounted fiber optic cables. The experimental results showed the validity of the crack-induced strain expression fitted to the distributed strains measured using an Optical Backscattering Reflectometry (OBR) system. As a result, precise estimations of the crack openings next to the optical cable location were achieved, as well as the monitoring of the optical cable response through following the strain lag parameter.
关键词： crack,distributed strains,crack opening,wedge splitting test,fiber optics sensors,strain transfer,imperfect bonding,concrete
更新于2025-09-23 15:19:57