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Effect of thickness and post deposition annealing temperature on the structural and optical properties of thermally evaporated molybdenum oxide films
摘要： In this paper, the influence of thickness and post deposition annealing temperature on thermally evaporated molybdenum oxide films has been studied. The X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) are used for crystal structural and surface morphological characterization of the films, respectively. The XRD analysis showed that the presence of α-MoO3 and MoO2 crystalline phase of the films annealed at elevated temperature ~ 250 °C after deposition. The optical constants are determined from UV–Vis transmission spectra. The optical band gap and Urbach energy is found to be temperature dependent. The refractive index of the films is estimated by the optical method as well as cross-sectional SEM image analysis. It is found that the refractive index of the films increases from ~ 1.70 to 2.03 with the decrease in film thickness from ~ 2.9 to 1.7 μm. It is also observed that the refractive index decreased from ~ 2.03 to 1.61 with the increase in post deposition annealing temperature from room temperature (RT) to ~ 250 °C. Moreover, extinction coefficient, optical conductivity, porosity, and film density are investigated as a function of source-substrate distance and post deposition annealing temperature. The Photoluminescence (PL) properties of the films are also investigated by recording spectra under the excitation wavelength at 250 nm.
关键词： Optical constants,Molybdenum oxide,X-ray diffraction,Thermal evaporation,Scanning electron microscope
更新于2025-09-23 15:22:29
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[IEEE 2018 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium) - Boston, MA, USA (2018.7.8-2018.7.13)] 2018 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium) - Sub-Diffraction Holographic Imaging with Resonant Scatterers in Proximity of the Objects
摘要： To overcome the well-known 'diffraction limit' in the resolution of electromagnetic imaging systems, we propose the use of resonant near-field scatterers incorporated in the holographic imaging techniques. These scatterers convert a portion of the evanescent spectrum in the proximity of the object to propagating spectrum which is measurable by the antenna in the far-field.
关键词： microwave and millimeter wave imaging,sub-diffraction imaging,resonant scatterers
更新于2025-09-23 15:22:29
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Characterization of the morphology of titanium and titanium (IV) oxide nanolayers deposited on different substrates by application of grazing incidence X-ray diffraction and X-ray reflectometry techniques
摘要： X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXRD) and X-ray reflectometry (XRR) techniques were applied for analysis of titanium (Ti) and titanium (IV) oxide (TiO2) nanolayers with thickness of 25 nm, 50 nm and 75 nm deposited on silicon, quartz and BK7 glass substrates. The aim of studies was investigating the crystal structure and morphology of the nanolayers in dependence on the substrate type. The chemical phases of nanolayers and substrates were determined by using the XRD and GIXRD measurements. The benefits of applying low angle GIXRD and XRR analytical techniques, both for substrate and nanofilm analysis, is discussed based on theoretical calculations and simulations. Additional, analytical capabilities of the XRR technique to nanolayer and substrate morphology analysis are presented. Simulated XRR curves for titanium (Ti) and titanium (IV) oxide nanolayers are discussed depending on the substrate type as well as the substrate and nanolayer roughnesses. Experimental reflectometry curves are presented for all titanium and titanium (IV) oxide nanolayers deposited on the different substrates. As the result of the XRR analysis, the nanolayer thickness and roughness together with substrate roughness are estimated. The mean values of the Ti and TiO2 layer thickness and roughness are presented for all studied samples. The largest roughness, both for nanolayers and for substrates, is obtained for BK7 glass material. In the manuscript, sample properties, experimental setups and measurement conditions are presented in details.
关键词： Titanium nanolayers,Titanium (IV) oxide nanolayers,Layer ion modification,X-ray reflectometry,Grazing incidence X-ray diffraction,Silicon, quartz substrates
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE 4th International Forum on Research and Technology for Society and Industry (RTSI) - Palermo, Italy (2018.9.10-2018.9.13)] 2018 IEEE 4th International Forum on Research and Technology for Society and Industry (RTSI) - Structural and Optical Behaviour of MAPbI<inf>3</inf> Layers in Nitrogen and Humid Air
摘要： The tendency of MA+-containing perovskites to degradation under humid air is still the main challenge which limits the durability of technologies. We indeed frame the behavior of MAPbI3 layer through structural and optical characterization under thermal cycles and using the environmental composition as a variable parameter (humid air, N2, Ar, O2). Within the temperature range explored (RT-80°C) we likely approach the thermal operation of the material under the sun and find that the degradation mechanism is linked to the action of water molecules by the formation of lattice defects. They rise the lattice disorder, especially at the crossover of the tetragonal to cubic transition wherein an acceleration of the degradation kinetics is observed. Nitrogen can help rationalizing solutions to stabilize the materials even at this critical transition step, since it behaves as more than an inert species.
关键词： Spectroscopic Ellipsometry,Photovoltaics,X-ray diffraction,Hybrid Perovskites,Stability,Thermal Cycle
更新于2025-09-23 15:22:29
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Structural, energetic and spectroscopic studies of new luminescent complexes based on 2-(2′-hydroxyphenyl)imidazo[1,2- <i>a</i> ]pyridines and 1,2-phenylenediboronic acid
摘要： Three new blue-luminescent complexes of selected imidazo[1,2-a]pyridine derivatives and 1,2-phenylenediboronic acid have been synthesized and structurally characterized using single-crystal X-ray diffraction. Additionally, the crystal structures of two of the (N,O)-donor compounds have been evaluated for the first time. The crystal packing and molecular motifs observed in the studied crystals have been thoroughly analysed, including computational studies, and are also discussed within the context of analogous systems reported in the literature. It appears that the new compounds form different crystal networks with regard to the asymmetric unit content and packing, although some similarities can be found. In all cases a typical centrosymmetric dimer bound via boronic acid groups is formed, characterized by an interaction energy of about -80 kJ mol-1, while the 2-(2'-hydroxyphenyl)imidazo[1,2-a]pyridine complex and its methoxy derivative form solvate structures, somewhat resembling the previously studied 8-oxyquinolinate analogues. As far as the spectroscopic properties are concerned, the lowest energy excitation observed in the studied complexes is based on the highest occupied molecular orbital–lowest unoccupied molecular orbital transition, and both these molecular orbitals are centred predominantly on the (N,O)-donor species according to the results of time-dependent density functional theory. Thus, the charge transfer observed for the 8-oxyquinolinate equivalents does not occur in these cases. Consequently, the spectroscopic behaviour of the series is very much comparable with that of the parent imidazo[1,2-a]pyridine derivatives, if the excited-state intramolecular proton-transfer process does not take place, as shown by the absorption and emission spectra collected in toluene and acetone solutions. Complexation causes a reduction in the Stokes shift compared with the respective (N,O)-donor molecules.
关键词： periodic calculations,TDDFT,UV–Vis spectroscopy,X-ray diffraction,time-dependent density functional theory,spectroscopic properties,luminescent boron complexes,transferred aspherical atom model (TAAM) refinement
更新于2025-09-23 15:22:29
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Electrical Properties of Midwave and Longwave InAs/GaSb Superlattices Grown on GaAs Substrates by Molecular Beam Epitaxy
摘要： In the present work, we report on the in-plane electrical transport properties of midwave (MWIR) and longwave infrared (LWIR) InAs/GaSb type-II superlattices (T2SLs) grown by molecular beam epitaxy (MBE) system on GaAs (001) substrate. The huge lattice mismatch between the T2SL and GaAs substrate is reduced by the growth of GaSb buffer layer based on interfacial misfit array (IMF) technique. In order to compensate the strain in the InAs/GaSb T2SL, we utilized a special shutters sequence to get InSb-like and GaAs-like interfaces. It is found that the MWIR InAs/GaSb T2SL exhibits a p- and n-type conduction at low and high temperatures, respectively. Interestingly, the conduction change temperature is observed to be dependent on the growth temperature. On the other hand, LWIR T2SL conduction is dominated only by electrons. It is important to note that the dominant scattering mechanism in LWIR T2SL at low temperatures is the interface roughness scattering mechanism.
关键词： Hall effect,High-resolution X-ray diffraction,Type-II superlattices,Molecular beam epitaxy
更新于2025-09-23 15:22:29
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Fabrication and Photoluminescence Properties of Monodispersed SiO2@SrAl2Si2O8:Eu2+ Core-Shell Submicron Spheres
摘要： Nanocrystalline SrAl2Si2O8:Eu2+ phosphor layers were coated on the surface of preformed submicron silica spheres by sol-gel method. The resulted monodispersed SiO2@SrAl2Si2O8:Eu2+ core-shell submicron spherical phosphors were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and photoluminescence spectra. The XRD results demonstrated that the SrAl2Si2O8:Eu2+ layers began to crystallize on the SiO2 spheres at 900 °C and the crystallinity increased with raising the annealing temperature. The obtained monodispersed core-shell spherical phosphors have perfect spherical shape with narrow size distribution (average size 500 nm). The Eu2+ shows a strong photoluminescence (dominated by 4f65d1 → 4f7 red emission at 390 nm) due to an efficient energy transfer from vanadate groups to Eu2+. The photoluminescence intensity of Eu2+ increases with raising the annealing temperature.
关键词： Nanostructures,Sol-gel processes,Optical properties,X-ray diffraction,Phosphers
更新于2025-09-23 15:22:29
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Temperature effect on structural, optical and NH<SUB align="right">3 gas sensing properties of TeO<SUB align="right">2 thin films
摘要： TeO2 thin films with different temperatures (400, 450 and 500°C) were deposited on glass substrates by thermal evaporation technique from a Te powder. XRD patterns indicate that as the temperature increases, the crystallisation improves. Observing the images obtained by SEM, it is seen that the grain size decreases as the temperature increases. The optical energy gap of the films was determined from transmittance and reflectance spectra. The optical energy gap decreased continuously from 3.95 eV to 3.80 eV with increasing temperature. Studying the effect of deposition temperature on NH3 gas measurement, it became obvious that as the deposition temperature increases, the sensitivity increases and the response and recovery times decrease.
关键词： scanning electron microscope,XRD,thin films,sensitivity,X-ray diffraction,energy gap,SEM,optical
更新于2025-09-23 15:22:29
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Optical diffraction radiation from a dielectric and a metal nanowire excited by a modulated electron beam
摘要： The optical diffraction radiation that accompanies the motion of a modulated beam of electrons near a dielectric and silver nanowire scatterers is investigated in the two-dimensional formulation. Our goal is to compute the field in the near and far zones and analyze how it depends on electron beam parameters. We demonstrate the excitation of internal resonances of such a scatterer that can be useful in the design of nanoscale non-invasive beam position monitors.
关键词： Plasmon resonance,Diffraction radiation,Nanowire scatterers,Total scattering cross-section,Absorption cross-section,Smith–Purcell effect,Surface wave
更新于2025-09-23 15:22:29
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Photochromic properties in silver-doped titania nanoparticles
摘要： The Ag-doped TiO2 nanoparticles were synthesized at room temperature using a solution of titanium isopropoxide and silver nitrate as precursors. The inclusion of Ag in the nanocrystalline TiO2 lattice was systematically analyzed both from a morphological and a structural point of view. Raman spectroscopy, electron microscopy, electronic diffraction and x-rays allow us to testify that the dopant Ag does not modify the nanocrystalline anatase tetragonal structure of the nanoparticles, but causes a small distortion of the structure. UV–vis spectroscopy allowed to analyze the optical properties of the obtained nanoparticles. Kubelka Munk’s model allowed the interpretation of diffuse reflectance spectra. We have obtained a very different system from the hetero-system Ag-TiO2 described in the literature, but it shows an interesting photochromic behaviour. Ag-doped TiO2 nanoparticles darken and whiten under UV light and visible light, respectively, in a very fast way. A simple kinetic model has been used to process experimental data and describe the observed photochromic process and to determine the darkening and whitening constants.
关键词： photochromism,electron diffraction,nanoparticles,optical properties,Raman spectroscopy
更新于2025-09-23 15:22:29