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Elongated Nanodomains and Molecular Intermixing Induced Doping in Organic Photovoltaic Active Layers with Electric Field Treatment
摘要： The effects of the electric-field-assisted annealing on the bulk heterojunction nano-morphology in the P3HT/PCBM active layer of the organic photovoltaic cells (OPVCs) are presented here. It was widely accepted that the electric-field-assisted annealing will facilitate the P3HT, the polar polymer, to be better crystalline to enhance the charge mobility, hence the improvement of the OPVC performance. The influences on the nano-morphology of the electron donor and accepter domains are not well understood. Here, using the cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/S), the electric-field-assisted annealing treatment is found to influence the molecular domains to be elongated along the direction of the external electric field. The elongation of the molecular domains is believed to facilitate the domain percolation, which causes higher charge mobility, hence the higher short-circuit current density (Jsc). On the other hand, it was also observed that the electronic properties of the P3HT-rich and PCBM-rich domains in the electric-field-assisted annealed samples showed smaller energy band gaps and smaller molecular orbital offset between the two domains, which is believed to decrease the open circuit voltage (Voc) and negatively impact the OPVC performance. Based on the X-ray diffraction (XRD) and small angle X-ray scattering (SAXS) results, the altered electronic properties are argued to be due to the molecular intermixing induced doping effects. These results point out competing factors affecting the OPVC performance with the electric-field-assisted annealing treatment.
关键词： Bulk heterojunction,Cross-sectional scanning tunneling microscopy,Organic Solar Cells,X-ray Diffraction,Small Angle X-ray Scattering,Nanomorphology
更新于2025-09-12 10:27:22
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[IEEE 2019 IEEE 32nd International Conference on Micro Electro Mechanical Systems (MEMS) - Seoul, Korea (South) (2019.1.27-2019.1.31)] 2019 IEEE 32nd International Conference on Micro Electro Mechanical Systems (MEMS) - Diversified and Precise Plasmonic Color Tuning by Three-Dimensional Air-Gap Nanocavities
摘要： We report a new arrayed three-dimensional (3D) air-gap nanocavities with multiple tunable geometrical parameters. Light is tightly confined into the nanocavities and strong surface-plasmon coupling is introduced, realizing narrow band resonance. Vivid plasmonic colors are generated, and can be tuned by multiple geometrical parameters of the 3D nanocavities, including shapes, separations, and heights. What’s more, the surface-plasmon coupling resonance has different dependence on different variable geometrical parameters. So, multi-dimensional color tuning with different spectral sensitivities is realized by proper and precise structural design, leading to both broad gamut and sophisticated plasmonic color printing at the optical diffraction limit.
关键词： plasmonic color tuning,surface-plasmon coupling,color printing,optical diffraction limit,3D air-gap nanocavities
更新于2025-09-12 10:27:22
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Simulation of Self-focusing of Femtosecond Laser Pulses with Normal Dispersion in Air Using the Diffraction-Beam Tube Approach
摘要： Based on numerical simulation and qualitative analysis, the effect of the group velocity dispersion on the formation of light structures during self-focusing and filamentation of femtosecond Ti:sapphire laser pulses in air is studied. The main features of the filamentation have been determined at various pulse duration, initial beam radii, and peak radiation powers based on the results of numerical solutions of the nonlinear Schr?dinger equation in a Kerr-plasma dissipative dispersion medium and using the diffraction-beam tube approach. Dispersion is detected in the cases where the dispersion length is not a minimum at the scale of the process. It is shown that the relative (normalized to Rayleigh length) coordinate of the beginning of filamentation increases as the dispersion distortions of the pulse increase, and the filamentation channel length is reduced. For shorter laser pulses (tens of femtoseconds), the filamentation ceases as the laser beam radius increases. The size of the energy-replenishing diffraction-beam tube and the angular divergence of postfilamentation light channels increase for this class of pulses.
关键词： filamentation,self-focusing,femtosecond laser pulses,diffraction-beam tube,normal dispersion
更新于2025-09-12 10:27:22
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Fabrication of diamond diffractive optics for powerful CO2 lasers via replication of laser microstructures on silicon template
摘要： New approach to fabricate diamond diffractive optical elements (DOEs) with continuous relief for powerful CO2 lasers is proposed and tested. It involves short-pulse laser microstructuring of a silicon wafer, which further is used as a substrate for polycrystalline diamond growth in a microwave plasma-assisted CVD process. After fine mechanical polishing of the growth side of the diamond film, the silicon substrate is removed via chemical etching. Two different DOEs providing close to 100% diffraction efficiency were fabricated with this technique: cylindrical Fresnel lens with kinoform surface profile and three-beam splitter with continuous microrelief. Optimization of the laser processing conditions has made possible to reduce the final roughness of the structured diamond surface to 200-400 nm depending on the local relief depth (0-7 μm). Both DOEs tested with a CO2 laser have demonstrated high transparency and diffraction efficiency, as well as low radiation scattering of the IR radiation at the surface irregularities.
关键词： laser microstructuring,diffraction efficiency,CVD process,diamond diffractive optics,CO2 lasers,silicon template
更新于2025-09-12 10:27:22
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Facile growth of SnS and SnS0.40Se0.60 thin films as an absorber layer in the solar cell structure
摘要： SnS (S1) and SnS0.4Se0.6 (S2) thin films were prepared using thermal evaporation on annealing at 523 K of the thermally deposited films. Compositional analysis of the films reveals the formation of SnS and SnS0.40Se0.60 phase. X-ray diffraction results demonstrate the formation of orthorhombic structure corresponding to SnS and SnS0.40Se0.60 phase. Moreover, a decrease in the intensity of SnS0.40Se0.60 peaks as compared to those of SnS was observed. Thus, causes insertion of selenium (Se) atoms in SnS lattice and results in the modification of lattice parameters. These structural modifications leads to variations in crystallite size, lattice strain and dislocation density, thus, confirms the formation of ternary SnS0.40Se0.60 phase. The changes corresponding to optical parameters are also observed in the films in the form of lower transmission, bandgap value and absorption coefficient on Se insertion. Moreover, both the films exhibit absorption coefficient >105 cm?1 with bandgap values of 1.44 and 1.23 eV and found suitable for absorption in solar cell.
关键词： Tin,Thermal evaporation,X-ray diffraction,Solar absorbers,Bandgap,SnS1?xSex
更新于2025-09-12 10:27:22
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PLASMONIC DIFFRACTION FIELD PATTERN IMAGING COULD RESOLVE ULTRA-SENSITIVE BIO-INFORMATION
摘要： Subwavelength nanohole arrays have been very attractive for label-free biosensing applications as they offer simplicity and flexibility in read-out scheme. Recently, platforms employing imaging-based devices integrated to custom-made light sources and plasmonic nanohole array substrates have been proposed as strong candidates to increase throughput by allowing simultaneous evaluation of binding interactions. Despite their high-throughput and multiplexed nature, these platforms dramatically suffer from sensitivity compared to classical spectrometer-based systems. In this article, we introduced a highly sensitive and plasmonic imaging-based platform that can work with very low analyte concentrations. The system employs a tunable optic filter integrated to a CMOS camera that records diffraction intensity patterns of the transmitted light from a plasmonic biochip composed of periodic nanohole arrays. Monitoring diffraction field intensity variations that correspond to transmission values at different wavelengths within the spectrum, we have successfully reconstructed the transmission spectrum of nanohole arrays. Using bulk solutions, we achieved spectral shifts within the reconstructed spectrum that yields refractive index sensitivities very close to the one calculated from the original spectrum obtained with a spectrometer. Similarly, we showed that our platform yields spectral shift amounts very close to the original one upon the attachment of protein mono- and bilayers. By monitoring plasmonic diffraction field intensity images, created through a very sharp illumination light source overlapping with the plasmonic mode of interest, we experimentally achieved sub-1 ng/mL limit-of-detection. Integrating the plasmonic biochip to a microfluidic chamber, we could monitor protein binding kinetics and determined the associated binding parameters very close to the ones obtained through the classical spectrometer-based analyses. Simultaneously monitoring multiple sensing spots in real-time within the same plasmonic biochip, we demonstrated the high-throughput capability of our plasmonic imaging-based technique. Our results showed the possibility of developing plasmonic read-out platforms that could provide high-throughput and multiplexed biosensing without losing sensitivity when integrating large-scale plasmonic chips with multiple sensing locations to imaging-based devices.
关键词： Nanohole arrays,Plasmonics,Nanofabrication,Diffraction Field Monitoring,Label-free biosensing
更新于2025-09-12 10:27:22
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Controllable spatial array of optical needles with independent axial intensity distributions for laser microprocessing
摘要： Due to their high length to width ratio nondiffracting beams are usually perceived as “optical needles”. We construct an “optical needle” with an arbitrary longitudinal intensity distribution and change the spatial position of it in the focal region of a lens. Next, we introduce a spatial array of independent “optical needles” and report on physical limitations due to mutual interference of individual beams. We employ a spatial light modulator as a toy model of an actual geometrical phase element and experimentally observe controllable spatial arrays with various numbers and spatial separations of individual beam. Lastly, we examine the distortions caused by propagation through planar air-dielectric interface and attempt to compensate it.
关键词： Structured light,Focal lines,Diffraction,Optical Needle,Multiple focal spots,Optical engineering,Bessel beams
更新于2025-09-12 10:27:22
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Efficient Mode Multiplexer for Few-Mode Fibers Using Integrated Silicon-on-Insulator Waveguide Grating Coupler
摘要： We propose a novel and highly efficient multimode waveguide grating coupler which can simultaneously launch four channels including two polarizations of the linear polarized (LP) modes, LP01 and LP11 of a step-index few-mode fiber (FMF). The waveguide grating coupler on the silicon-on-insulator (SOI) platform is based on a subwavelength structure which was optimized using the genetic optimization approach with 2-dimensional finite-difference time-domain (2-D FDTD) simulations combined with the second?order effective medium theory (EMT). Simulations predicted the coupling efficiencies to be ?4.3 dB for LP01 mode and ?5.0 dB for the LP11 mode. The design was fabricated in a multi-project wafer (MPW) run for silicon photonics. Coupling efficiency of ?4.9 dB and ?6.1 dB was experimentally demonstrated for LP01 mode and LP11 mode, respectively. The proposed mode multiplexer is entirely passive and suitable for future applications with FMFs in space-division-multiplexing (SDM) networks.
关键词： few-mode fibers,space-division multiplexing,diffraction gratings,Integrated optics
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Light and Slow-Neutron Diffraction Properties of Holographic Nanodiamond Composite Gratings
摘要： Photopolymerizable nanoparticle-polymer composite (NPC) is a photonic nanocomposite material consisting of photopolymer uniformly dispersed with nanoparticles (e.g., SiO2 and ZrO2). The distribution of dispersed nanoparticles can be manipulated holographically by light. This technique, the so-called holographic assembly of nanoparticles in polymer, enables us to perform the single step formation of large area photonic lattice structures for photonic applications such as holographic data storage, holographic diffractive elements and nonlinear optics. Furthermore, we showed that holographic NPC gratings could control slow-neutron (cold and very cold neutron) beams for neutron interferometer. Here we demonstrate for the first time the use of nanodiamonds (NDs), an intriguing allotrope of carbon, in NPCs to construct holographic NPC gratings with very large refractive index modulation amplitudes (Δn) and thus to efficiently control light and slow-neutron beams. This is possible because NDs have very high bulk refractive index at optical wavelengths and very large coherent and very small incoherent scattering cross sections with low absorption at slow-neutron wavelengths.
关键词： holographic grating,photopolymer,diffraction,slow-neutron,nanodiamond
更新于2025-09-12 10:27:22
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Stress distribution in laser metal deposited multi-layer thick-walled parts of Ti-6Al-4V
摘要： The laser metal deposition is an additive manufacturing technology enabling the production of large scale complex parts without additional treatment like welding or machining. The study of the origin of the stress field during laser metal deposition is essential for solving a number of problems, including: the assessment of cold and hot cracking; prediction of the fatigue resistance, and the stress corrosion cracking. The quantitative study of transient and residual stresses in build parts is necessary for optimising the parameters of processing and post-production stress relieving heat treatment. Residual stress field in laser metal deposited 50-layer (4-pass per layer) wall of Ti-6Al-4V was analysed experimentally using neutron diffraction and numerically using finite element simulation. Long dwell time between passes and a rigid substrate was used in order to simulate conditions of large scale parts fabrication. An analysis of the calculated and experimentally measured residual stress field showed that near the edges of the buildup there is a region where all three components of stress field are tensile, and normal stress exceeds the yield stress by more than 25%. Moreover, normal plastic strain in this area are also tensile and reaches 2.5-3%. The longitudinal tensile stress closes to yield stress on almost the entire length of the several last layers near the top of the buildup. Residual stress field calculated using neutron diffraction data according to interplanar lattice distance obtained assuming plane stress approach has a satisfactory agreement with FE simulated results.
关键词： Neutron diffraction,Laser metal deposition,Simulation,Residual stress,Titanium alloy
更新于2025-09-12 10:27:22