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The Double PEC Wedge Problem: Diffraction and Total Far Field
摘要： Complex scattering targets are often made by structures constituted of wedges that may interact at near field. In this paper, we examine the scattering of a plane electromagnetic wave by two separated arbitrarily oriented perfectly electrically conducting wedges with parallel axes. The procedure to obtain the solution is based on the recently developed semianalytical method known as generalized Wiener–Hopf technique that allows a comprehensive mathematical model of the problem in the spectral domain avoiding multiple steps of interaction among separated objects. The numerical results are presented to validate the procedure in terms of spectral quantities, GTD/uniform theory of diffraction coefficients and total far fields for engineering applications. The structure is of interest in electromagnetic applications, in particular, to accurately predict path loss in propagation with diffraction phenomena.
关键词： electromagnetic diffraction,radar applications,wedges,propagation,electromagnetic shielding,wireless communication,Wiener–Hopf (WH) method,integral equations,EMC,near-field interactions,Antenna technologies
更新于2025-09-23 15:21:01
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Crystal structure and ferroelectric polarization of tetragonal (Bi <sub/>1/2</sub> Na <sub/>1/2</sub> )TiO <sub/>3</sub> –12BaTiO <sub/>3</sub>
摘要： We have investigated the crystal structure and ferroelectric polarization of (Bi1/2Na1/2)TiO3–12%BaTiO3 by high-resolution neutron powder di?raction Rietveld analysis and density-functional theory calculations. It is revealed that the sample has a ferroelectric distortion in tetragonal P4mm symmetry along with a large tetragonality c/a of 1.022. The A- and B-site atoms exhibit a cooperative o?-center displacement along the polar c-axis, which results in a large spontaneous polarization of 54 μC/cm2.
关键词： crystal structure,neutron powder diffraction,tetragonal (Bi1/2Na1/2)TiO3–12BaTiO3,density-functional theory,ferroelectric polarization
更新于2025-09-23 15:21:01
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Structure determination of substrate influenced silicon nano-ribbon growth
摘要： Using photoelectron diffraction (XPD), photoelectron spectroscopy (XPS), and low energy electron diffraction (LEED), we investigate the structure of silicon nano-ribbons grown on Au(1 1 0). We find that silicon forms two zigzag-terminated hexagonal chains along the [1 1 0]-substrate direction, while the gold substrate forms a bulk-typed surface reconstruction after silicon evaporation. Only two missing rows along the [1 1 0]-direction remain partially in their original structure at the Si/Au interface. Unlike silicon nano-ribbon formation on Ag(1 1 0), nano-ribbon growth on Au(1 1 0) is strongly substrate influenced by Van-der-Waals interaction and by AuSi bonding formation. This strong interaction leads to a substrate-driven hexagon formation, where the gold atoms are partially integrated into the ribbon structure. Besides the determination of the internal silicon nano-ribbon structure, we identify the origin of the two chemically shifted silicon components in the XPS spectra by deconvolving the diffraction pattern.
关键词： Photoelectron spectroscopy,Hexagonal chains,Nano-ribbon,Silicon,Photoelectron diffraction
更新于2025-09-23 15:21:01
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Wide-Angle Polarization-Independent Paratellurite-Based Acousto-Optic Laser Radiation Modulator
摘要： High-efficiency wide-angle polarization-independent acousto-optic diffraction of laser radiation in a paratellurite-based modulator is experimentally studied. The previously published main theoretical principles are confirmed. We have shown that the angular aperture of the acousto-optic modulator can be ~8° in an ultrasonic frequency range of 135–68 MHz depending on the light wavelength and 2°–5° in the range of 20–30 MHz. A wide-angle acousto-optic depolarized laser radiation modulator has been created that operates at a wavelength λ = 1.06 μ m with one output depolarized beam and an efficiency of no less than 90% for input radiation with an angular aperture of 30 mrad.
关键词： light polarization,angular diffraction range,anisotropic acousto-optic diffraction,acousto-optic modulator
更新于2025-09-23 15:19:57
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Precession Electron Diffraction and Orientation Phase Mapping of Assembled Ag/ZnO Nanoantennas
摘要： The manipulation of the geometrical and structural arrangement of the constituent’s elements on devices at nanoscale level is highly desirable for a precise monitoring of the opto-electrical properties exhibited for these nanomaterials. In fact, a great effort has being made to understand the coupling mechanisms on metal-semiconductors systems, most precisely at interfaces nanoscale level. For instance, it is well known that the multidirectional radiation pattern generated by the active elements on nanoantenna applications is highly dependent on both the structural and orientation distribution of the receiver elements as well as the passive element on the nanoscale device. For example, Wang, et al [1] have synthesized high order nanostructures in a hierarchical configuration to study the photo-induced optical properties of these systems in function of the ZnO concentration distributed along the silver nanowires. However, few is known about the structural coupling mechanisms between this metal-semiconductor heterojunctions. Thus, to understand the dynamic coupling at the interface level in the Ag/ZnO metal-semiconductor heterojunctions we report the epitaxial growing of zinc oxide nanorods on the pentagonal exposes faces of Ag nanowires resembling a hierarchal nanoantenna. Moreover, the studied of the growth mechanism in the active/contact faces of the metal-semiconductor heterojunction has been done by mapping simultaneously the dynamical electron diffraction pattern under in-situ precession electron diffraction at the heterojunction interface Ag/ ZnO nanosystem. Indeed, by indexing the dynamical diffraction patterns using orientational/phase mapping from the precessed electron diffraction data collected an orientational mapping has been retrieved showing the interfacial growing polar planes (0002) of ZnO nanorods on the pentagonal planes of silver nanowires with a mismatch between planes along the coupling interface. For completeness, grazing angle x-ray diffraction measurements on prepared substrates Ag/ZnO systems shown well-defined peaks associated to the main phases of ZnO nanorods and Ag nanowires respectively. A full understanding of the fit faces mechanism between Ag/ZnO along the mismatch direction undoubtedly will allow elucidating the mechanism through which the contact metal-semiconductor behaves at the heterojunction interface.
关键词： Nanoscale Devices,Ag/ZnO Nanoantennas,Metal-Semiconductor Heterojunctions,Orientation Phase Mapping,Precession Electron Diffraction
更新于2025-09-23 15:19:57
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p+ polycrystalline silicon growth via hot wire chemical vapour deposition for silicon solar cells
摘要： Hot wire chemical vapour deposition (HWCVD) is explored as a way of growing boron-doped silicon for photovoltaic devices. Deposition temperatures are measured using a custom-built monitoring system for two different filament configurations within the HWCVD tool. A refined fabrication process is presented, using an altered filament arrangement, that currently provides a maximum deposition temperature of 535 oC, for growing boron-doped silicon films via HWCVD, with the inclusion of a short post-deposition anneal at 800 oC for 2 minutes. Transmission electron microscopy reveals improvements in interfacial quality, as well as larger grains present after post-annealing treatments. In addition, re-crystallisation of as-deposited amorphous Si films under a short anneal is confirmed using Raman spectroscopy. The enhancements in morphology translate to a boost in current rectification based on our dark current-voltage measurements. This is further supported by secondary-ion mass spectrometry analysis, presenting p+ properties with uniform doping in the 1021 cm-3 region.
关键词： Selective area electron diffraction,Crystallisation,Emitter,Hot wire chemical vapour deposition,Silicon solar cells,Transmission electron microscopy
更新于2025-09-23 15:19:57
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Influence of defects on structural colours generated by laser-induced ripples
摘要： The colourisation of metallic surface which appears due to periodic surface patterns induced by ultrashort laser pulses is studied. Ripples due to the sub-micrometer size of their period act as a diffraction grating, generating structural colours. Carefully chosen strategy of the laser spot scanning allows us to mimic the nanostructures responsible for structural colours of some flowers on the metal substrate. We investigate the correlation between the colourising effects and the artificially-induced defects in the ripples structure and show that these defects can make the colours observable in a larger range of viewing angles. Further we address the influence of the processing parameters on the spectral profile of the reflected light.
关键词： structural colours,viewing angles,diffraction grating,defects,laser-induced ripples
更新于2025-09-23 15:19:57
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The Phase Behavior in the Active Layer of Small Molecule Organic Photovoltaics: The State Diagram of p-DTS(FBTTh <sub/>2</sub> ) <sub/>2</sub> :PC <sub/>71</sub> BM
摘要： A comprehensive study was undertaken to obtain a more fundamental understanding of the phase behavior of the p-DTS(FBTTh2)2:PC71BM system, used in small molecule organic solar cells, with a strong focus on the amorphous phase and its influence on crystallinity. Three dedicated thermal protocols were used in combination with advanced thermal analysis, solid-state NMR, and wide angle X-ray diffraction. Rapid cooling, to avoid structure formation and gain insight in the amorphous phase, and slow cooling, to promote structure formation, were used as limiting cases to explain the intermediate behavior after device processing from solution. A complete state diagram was developed and the glass transition (Tg) - composition relationship was determined. In the case of slow cooling and the procedure used for device processing, the rapid crystallization of p-DTS(FBTTh2)2 leads to an enrichment of the amorphous phase in PC71BM, increasing its Tg and causing vitrification of the mixed amorphous phase before crystallization when the total amount of PC71BM exceeds 70 wt%. The common processing additive 1,8-diiodooctane (DIO) was found to lead to a lower p-DTS(FBTTh2)2 crystallinity and smaller average crystal size. More importantly, it acts as a strong plasticizer, lowering Tg significantly and thus reducing the morphological stability of the p-DTS(FBTTh2)2:PC71BM mixtures.
关键词： p-DTS(FBTTh2)2:PC71BM,glass transition temperature,wide angle X-ray diffraction,phase behavior,crystallinity,amorphous phase,small molecule organic photovoltaics,thermal analysis,solid-state NMR,1,8-diiodooctane (DIO)
更新于2025-09-23 15:19:57
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Physicala??Chemical Properties of Self-Assembled Structures in Solution of Zinc Phthalocyanine and Bis-3-pentyl-PTCDI Derivative
摘要： For the first time, in this work, we succeed in synthesizing in solution a novel supramolecular self-assembled zinc phthalocyanine (ZnPc) and N,N′-bis(3-pentyl)-perylene-3,4,9,10-bis(dicarboximide) (bis-3-pentyl-PTCDI) system with improved light absorption and phosphorescence lifetime of the charge separated states up to 2.5 ms. Moreover, the structural and optical properties of undoped and doped with iodine ZnPc thin films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman analysis, and UV?vis spectroscopy. Analysis of ZnPc:I2:bis-3-pentyl-PTCDI blend in a 2:1 ratio shows that sandwich complexes between them result in improved bulk properties as compared to those of the single-component systems.
关键词： light absorption,Fourier transform infrared spectroscopy,UV?vis spectroscopy,bis-3-pentyl-PTCDI,X-ray diffraction,supramolecular self-assembly,X-ray photoelectron spectroscopy,zinc phthalocyanine,phosphorescence lifetime,Raman analysis
更新于2025-09-23 15:19:57
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Investigation on the microstructure and mechanical behaviors of a laser formed Nb-Ti-Al alloy
摘要： Nb-Ti-Al alloys have attracted much attention as a potential candidate for high-temperature structural applications beyond the scope of Ni-based superalloys. Previously, Nb-Ti-Al alloys were prepared by arc-melting or hot-pressing. In this study, laser forming of the Nb-23Ti-15Al alloy is explored, and the microstructure and mechanical behaviors are systematically investigated. The results indicate that the nearly defectless Nb-Ti-Al alloy with fine dendrites could be obtained through laser forming. Three phases, β, δ and Ti(O,C), present in the alloy, and the β/δ matrix displays a columnar microstructure. Moreover, the Ti(O,C) phase, a solid-solution of TiO or TiC, appears in the alloy. Ti(O,C) is formed due to the introduction of the O and C from the elemental powder, which has a face-centered cubic (FCC) structure and a moderate lattice parameter between that of TiO and TiC. Two morphologies of Ti(O,C), large cobblestone-like particles and small dispersive particles, are observed in the alloy. Forbidden reflections of δ phase occur due to double diffraction and slight superlattice reflections of β phase arise. Furthermore, refined β/δ phases and dispersed small Ti(O,C) result in higher microhardness and fracture toughness. In brief, our results indicate that laser forming is a potential method for manufacturing Nb-Ti-Al alloys with prominent properties.
关键词： Laser forming,Double diffraction,Mechanical behavior,Ti(O,C),Nb-Ti-Al alloy,Microstructure
更新于2025-09-23 15:19:57