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摘要： The basic and the charge density wave (CDW) structures of the monoclinic NbS3-II polymorph were studied by synchrotron x-ray diffraction, ab initio calculations, simulation of electron diffraction patterns, and by atomic-resolution transmission electron and low-temperature scanning tunneling microscopies. It is con?rmed that the basic structure belongs to the space group P 21/m and is described with a unit cell, formed of four pairs of symmetry-related trigonal prismatic (TP) columns [a0 = 0.96509(8) nm, b0 = 0.33459(2) nm, c0 = 1.9850(1) nm, and β0 = 110.695(4)?]. The incommensurate components of the two CDWs, (cid:3)q1 = (0, 0.298, 0) and (cid:3)q2 = (0, 0.352, 0), are related as q1b + 2q2b ≈ 1. Both CDWs form their own modulation patterns with unit cells (am = 2a0, bm = b0/qjb, cm = c0, βm = β0) and are ordered along adjacent isosceles TP columns either pairwise or with both columns modulated by either the (cid:3)q1 or (cid:3)q2 CDW only. The CDWs are ordered according to one of the two possible modulation pattern space groups, Cm or C2/m. If considered as long-period commensurate, the entire modulated structure with both CDWs included is described within experimental error with an enlarged unit cell (a = 2a0, b = 37b0, c = c0, and β = β0) and with all atoms displaced from their average positions in accord with the speci?ed modulation pattern.
关键词： synchrotron x-ray diffraction,ab initio calculations,charge density wave,scanning tunneling microscopy,transmission electron microscopy,NbS3-II
更新于2025-09-09 09:28:46
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The Invention of an Optical Antenna—A Personal Reminiscence
摘要： The subject of this article is my personal path from the near-field optical (NFO) microscope to the optical antenna and its potential for modern optics.
关键词： breaking the diffraction limit,optical antenna,lifetime of Q-dots,nonlinearities,antenna resonance
更新于2025-09-09 09:28:46
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[IEEE 2018 IEEE International Conference on Semiconductor Electronics (ICSE) - Kuala Lumpur (2018.8.15-2018.8.17)] 2018 IEEE International Conference on Semiconductor Electronics (ICSE) - Bandgap Engineering of GaAsBi Alloy for Emission of up to 1.52 μm
摘要： Band gap engineering by incorporating bismuth into GaAs to form ternary GaAs1-xBix alloy was investigated. Series of GaAsBi samples with different Bi concentrations were grown by molecular beam epitaxy. Based on high resolution X-ray diffraction (HR-XRD) measurements, Bi concentration of up to 0.108 was successfully incorporated into the lattice. Sample with the highest Bi concentration, GaAs0.892Bi0.108, show room temperature photoluminescence (PL) emission with a peak wavelength of 1.52 μm and full-width-at-half-maximum (FWHM) of 89 meV. It was found that the incorporation of Bi into GaAs lattice affected both the conduction band as well as the valence band. The conduction band minimum reduces linearly by 23 meV/%Bi while the valence band maximum was best fitted by using the valence band anti-crossing (VBAC) model with coupling parameter, CBi of 1.65 eV.
关键词： band gap engineering,X-ray diffraction,molecular beam epitaxy,GaAsBi,photoluminescence
更新于2025-09-09 09:28:46
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The structure of near stoichiometric Ge-Ga-Sb-S glasses: A reverse Monte Carlo study
摘要： The structure of Ge22Ga3Sb10S65 and Ge15Ga10Sb10S65 glasses was investigated by neutron diffraction (ND), X-ray diffraction (XRD), and extended X-ray absorption fine structure (EXAFS) measurements at the Ge, Ga and Sb K-edges. Experimental data sets were fitted simultaneously in the framework of the reverse Monte Carlo (RMC) simulation technique. Short range order parameters were determined from the obtained large-scale configurations. It was found that the coordination numbers of Ge, Sb and S are around the values predicted by the Mott-rule (4, 3 and 2, respectively). The Ga atoms have on average 4 nearest neighbors. The structure of these stoichiometric glasses can be described by the chemically ordered network model: Ge-S, Ga-S and Sb-S bonds are the most important. Long Sb-S distances (0.3–0.4 ? higher than the usual covalent bond lengths) are observed, suggesting that Sb atoms can be found in various local environments.
关键词： RMC,Structure,Ge-Ga-Sb-S,Diffraction,Chalcogenide glasses,EXAFS
更新于2025-09-09 09:28:46
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Máscara espectrográfica para registro digital de espectros de fontes brilhantes
摘要： In this work we present schematic diagrams for the construction of a spectrographic mask attachable to a camera objective in order to capture spectra using simple CD or DVD gratings. The mask is made of two parts: an adapter ring and elbow-shaped blockage for suitable registration of spectra in the lab and outdoors. By using a free software, we analyze and discuss the calibration of the wavelength scale of the solar spectrum, which allows us to identify many chemical elements in it. In the conclusion, we further discuss some interesting projects to be carried out by students using the idea.
关键词： Spectrum,Spectroscope,Image Processing,Diffraction Gratings,Optics
更新于2025-09-09 09:28:46
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New W-band Scattering Measurement System: Proof of Concept and Results for 2D Objects
摘要： The paper deals with a detailed study of an original system dedicated to scattering measurements of millimeter waves in the W-band. The system’s main innovations lie in its high-precision swivel arm, semi-anechoic environment, flexibility for positioning the object on the measurement tower, as well as the post-processing developed to correct measurement errors. We use canonical objects, i.e. cylinders, for tests and evaluate measurement errors and system performance by comparisons with the theoretical scattered field, which has an analytical expression. For the sake of generality, we work with both VV and HH-polarizations. We propose a complete workflow that performs noise suppression and positioning error correction, relying on two quantities: 1) the cut-off frequency of a low pass filter and 2) the pre-determination of the position of the device under test (DUT). The originality of our approach is that both quantities are fully-defined by the measurement data without a priori knowledge of the DUT. Since the different steps of the workflow are generic, it can easily be transposed to any scattering measurement system. Finally, once corrected, measurements at 75, 95, and 110 GHz exhibit signal-to-noise ratios (SNR) of close to 15 dB for dielectric cylinders and up to 25 dB for metallic ones. To the best of our knowledge, this is the first time that such values have been exhibited in the W-band.
关键词： Millimeter wave measurements,Measurement errors,Electromagnetic diffraction
更新于2025-09-09 09:28:46
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Mathematical Modeling of Droplet Formation, Evaporation, and Film Growth to Study Crystallite Size and Film Thickness of Spray Pyrolysis Deposited TiO<sub>2</sub> Thin Films
摘要： The pure TiO2 thin films were successfully deposited onto a glass substrate by using modified spray pyrolysis system. The TiO2 thin films were deposited at temperature 350?C using Titanium trichloride precursor solutions of concentration 0.075 M, 0.1 M, and 0.125 M. Also, TiO2 thin films with precursor solutions of concentration 0.1 M were deposited at different deposition temperature 350?C, 400?C, and 450?C. The prepared samples were further annealed at 500?C for 2 h to improve crystallinity. The XRD study revealed that the deposited TiO2 thin films were polycrystalline and showed anatase phase with pre-dominant (101) peak. The crystallite size calculated from XRD was found to increase with increase in precursor solution concentration. The mathematical model to calculate crystallite size and film thickness were developed and the predicted results were compared with experimental results. The experimentally calculated crystallite size and thickness was in good agreement with the predicted results. The details of mathematical model and calculations TiO2 thin films for were discussed in detail.
关键词： Growth,Liquid phase epitaxy,Crystallization,Titanium oxide,X-ray diffraction,Semiconducting films
更新于2025-09-09 09:28:46
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Linear and Third Order Non-Linear Optical Properties of Urea Salicylic Acid Crystal
摘要： An organic non-linear optical crystal urea salicylic acid was grown by slow evaporation method using the mixed solvent of ethanol and water in equal ratio. The lattice parameters of urea salicylic acid crystal were obtained by single X-ray diffraction study. The optical transmittance study revealed the good transmission window of the urea-salicylic acid and its suitability for optical applications. The non-linear refractive index, n2, absorption coefficient, β and third order susceptibility, χ(3) have been measured through the Z-scan technique with He-Ne laser at 632.8 nm. The grown urea salicylic acid crystal exhibits two photon absorption and self-defocussing performance.
关键词： Crystal growth,X-ray diffraction,Optical properties
更新于2025-09-09 09:28:46
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Investigation on Physical Properties of Semiorganic Nonlinear Optical Glycine Zinc Sulfate Single Crystal
摘要： Nonlinear optical single crystals of Glycine Zinc Sulfate (GZS) were grown by slow evaporation technique. Single crystal X-ray diffraction analysis revealed the crystal system and lattice parameter values. Powder X-ray diffraction analyses have been carried out and the diffraction patterns have been indexed. The optical properties of the crystals were determined using UV-Visible spectroscopy. Optical constants such as band gap, refractive index, extinction coefficient and electric susceptibility were determined from UV-Visible spectroscopy. The refractive index was determined using Brewster’s angle method. Hardness of the GZS crystal was estimated by Vicker’s hardness studies. Second Harmonic Generation (SHG) of GZS crystal was investigated by Kurtz powder technique. The dielectric constant and dielectric loss measurements were carried out for different temperatures and frequencies. The photoconductivity studies confirm that the grown crystal has negative photoconductivity nature. In order to investigate the growth mechanism and surface features, etching studies are carried out for the crystal.
关键词： NLO,single X-ray diffraction,SHG,UV-Vis-NIR spectrophotometer,dielectric loss studies,dielectric constant
更新于2025-09-09 09:28:46
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Structural Characterization of Two New Quaternary Chalcogenides: CuCo2InTe4 and CuNi2InTe4
摘要： The crystal structure of the chalcogenide compounds CuCo2InTe4 and CuNi2InTe4, two new members of the I-II2-III-VI4 family, were characterized by Rietveld refinement using X-ray powder diffraction data. Both materials crystallize in the tetragonal space group I 4 2m (No. 121), Z = 2, with a stannite-type structure, with the binaries CoTe and NiTe as secondary phases.
关键词： structural characterization,chemical synthesis,alloys,semiconductors,X-ray powder diffraction
更新于2025-09-09 09:28:46