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Gram scale synthesis of monoclinic VO2 microcrystals by hydrothermal and argon annealing treatment
摘要： We report gram scale synthesis of 100 % phase fraction of VO2 (M) monoclinic in powder form with reversible phase transition by combining hydrothermal method and Ar annealing at high temperature. Optimization of single phase VO2 (M) growth and its phase transition characteristics have been analysed systematically by varying growth parameters such as time, synthesis temperature and post growth annealing conditions. Argon annealing of hydrothermally grown VO2 powders at 800°C found to play key role in obtaining VO2 (M) phase in gram scale with characteristic phase transition temperature of 68°C. In-situ TEM has been performed to investigate the microstructure and phase change across the annealing temperature. Detailed characterizations have been carried out to correlate the phases, microstructure and transition temperature of VO2 with respect to growth parameters.
关键词： metal-insulator transition,annealing treatment,monoclinic VO2,in-situ TEM,microcrystals,Scalable synthesis
更新于2025-09-23 15:21:21
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Photocatalytic degradation of 4-chlorophenol with the use of FTO/TiO2/SrTiO3 composite prepared by microwave-assisted hydrothermal method
摘要： Microwave-assisted hydrothermal method was applied to obtain SrTiO3 photocatalyst by transformation of a thin TiO2 layer deposited on the conducting solid substrate (FTO-glass) via dissolution-precipitation reaction in alkaline solution. The influence of Sr2+ ions concentration on crystallinity, composition as well as photoelectrochemical and photocatalytic properties of the resultant materials was investigated. The XRD studies indicated the presence of some amount of co-deposited SrSiO3 due to reaction of metasilicates released from the glass substrate (not covered with FTO film). However, the process of glass dissolution was substantially prevented by protection of the back side of the sample with a Teflon tape. The best activity in photodecomposition of 4-chlorophenol under irradiation with 365 nm diode was obtained for FTO/TiO2/SrTiO3 composite fabricated in 6 h synthesis in the solution containing 0.1 M Sr(NO3)2, at temperature of 180 °C. The photoelectrochemical properties of the composites and FTO/TiO2 electrode were studied in the solution of Na2SO4 under illumination with a xenon lamp. The increased photocurrent density and longer electron lifetime for the hybrid system in comparison to those of TiO2 was discussed in terms of suppressed recombination rate due to formation of TiO2/SrTiO3 interface. It was also found that the side product, SrSiO3, reveals an excellent adsorption properties with respect to methylene blue and therefore, the system SrTiO3/TiO2/FTO/glass/SrSiO3 may be used as bifunctional composite for adsorption and photocatalysis.
关键词： 4-Chlorophenol photodecomposition,Photocatalysis,SrSiO3,Photoelectrochemical properties,Microwave-assisted hydrothermal synthesis,TiO2/SrTiO3,Electron lifetime
更新于2025-09-23 15:21:21
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[IEEE 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Odessa, Ukraine (2018.9.4-2018.9.7)] 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Active Aperture Synthesis Radar for High Spatial Resolution Imaging
摘要： To solve problems of high-precision mapping of spatially extended objects regardless of weather conditions and time of day, radar imaging systems are used. The globality and efficiency of the survey is provided by the placement of radars on aerospace carriers. At the same time, there has been a proliferation of side-scan radars (providing a wide viewing range with a low spatial resolution) and antenna aperture synthesis radars (these provide high resolution in spatial coordinates, which depends on the type of survey). Radars used for imaging are classified according to various characteristics determining their advantages and disadvantages. Among such features, we can also distinguish the radar viewing area, which is currently limited to angles of 15° to 60° to the right and left of the observation in the nadir. The viewing range from -15° to +15° from the nadir is characterized by a low resolution in range and traditionally is not visible by these radars (the so-called "blind zone"). In this regard, an alternative system for building radar images from aerospace carriers is proposed. It will provide imaging with high angular resolution of the viewing range from -15° to +15° from the nadir. The main feature of the developed radar lies in the signal processing algorithm that combines methods of active (the presence of probing UWB signal) and passive (aperture synthesis) radiolocation. In addition, the radar implements a new method of "spectral aperture synthesis," which allows from processing of UWB signals with the continuum spectrum to processing multi-band signal processing.
关键词： radar mapping,active aperture synthesis,aerospace systems of remote sensing,radar imaging methods
更新于2025-09-23 15:21:21
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[IEEE 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Odessa, Ukraine (2018.9.4-2018.9.7)] 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Combined Wide-Angle Scanning by a Two-Dimensional Dipole Array
摘要： An analytical solution of an impedance synthesis problem for a two-dimensional dipole antenna array is obtained. The array consists of thin impedance electric dipoles whose centers are located at nodes of a planar rectangular grid with double periodicity. Radiation patterns of each dipole in the array does not differ from that of an isolated dipole. A new method for wide-angle scanning of the array radiation pattern, combining the simultaneous variation of phases of the excitation currents in the dipoles and of their surface impedances is proposed.
关键词： thin impedance dipole,flat two-dimensional antenna array,wide-angle scanning,radiation pattern,wave zone,impedance synthesis method
更新于2025-09-23 15:21:21
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Soluble and insoluble polymer-inorganic systems based on poly(methyl methacrylate), modified with ZrO2-LnO1.5 (Ln = Eu, Tb) nanoparticles: Comparison of their photoluminescence
摘要： The study of the lanthanide ion luminescence as a function of their environment in polymer-inorganic composites is necessary for better understanding of the electron energy transfer processes in a condensed state. From a practical point of view, these materials are promising for optics and medicine. The nanoparticles of ZrO2-LnO1.5 (Ln = Eu, Tb) solid solutions were synthesized by hydrothermal method. The surface functionalization of the obtained nanoparticles by vinyl groups was carried out using 3-(trimethoxysilyl)propyl methacrylate. Soluble and cross-linked composites based on poly(methyl methacrylate) with ZrO2-LnO1.5 nanoparticles were synthesized using radical polymerization in solution and bulk. Molecular weight, thermal stability, and microhardness of the obtained composite materials were determined. The influence of both the polymerization conditions and the forming composite structure on the lanthanide ion photoluminescence in ZrO2 nanoparticles covalently bonded to the polymer matrix was studied. The combination of ZrO2-EuO1.5 and ZrO2-TbO1.5 nanoparticles in the poly(methyl methacrylate) resulted in the production of composites with photoluminescence spectra overlapping the red and green regions of the visible range. It was shown that the structure of the composite affects the absorbing capacity of luminescent centers and allows shifting the excitation spectrum in the longer wavelength region.
关键词： hydrothermal synthesis,poly(methyl methacrylate),rare-earth ions,solid solutions,zirconia,hybrid nanomaterials
更新于2025-09-23 15:21:21
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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) - Engineering the Properties of Nb<inf>2</inf>O<inf>5</inf>-ZnO Nanostructures via Dual Synthesis Techniques
摘要： In this paper, dual techniques; anodization and hydrothermal, were introduced to synthesize the Nb2O5-ZnO nanostructures. The purpose of this research is to engineer the properties of the Nb2O5-ZnO nanostructures which can offer new optical and electrical behaviors and also lead to large surface area. Synthesis of Nb2O5 has been conducted by anodizing the Niobium foil in the electrolyte containing NH4F and ethylene glycol. Meanwhile, ZnO was hydrothermalized with Zinc Nitrate precursor solution for 18 hr at different temperatures. All samples were characterized using FESEM, XRD and UV-Vis absorbance spectra. The morphological and properties changes of the Nb2O5-ZnO nanostructures are systematically investigated as a function of hydrothermal temperature.
关键词： ZnO,dual synthesis,anodization,Nb2O5,nanostructure,hydrothermal
更新于2025-09-23 15:21:21
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A Synthesizable Constant Tuning Gain Technique for Wideband LC-VCO Design
摘要： In this paper, an iterative method is proposed for the optimization of wideband voltage-controlled oscillators (VCOs). The proposed method attempts to improve two significant performance metrics of wideband VCOs, i.e., the non-uniform band distribution and the non-constant tuning gain KVCO. To address these non-ideality issues, we introduce the deviation as a prior knowledge for calibration in each iteration step. The optimal capacitor array weighting plan can be asymptotically approached through multiple iterations. To demonstrate the efficacy of the proposed method, we use it to implement a 1-to-2.4-GHz LC-VCO and achieve a frequency tuning range of 82.4%. The optimized LC-tank involves 64 mixed cells, and each cell contains 2-bit binary-weighted switching capacitors, leading to 256 tuning bands. The LC-VCO with the synthesized tank achieves uniform frequency steps around 5 MHz with the relative error within ±4.4%. Meanwhile, the tuning gain KVCO is around 10 MHz/V with the relative error within ±3.2%. For this LC-VCO design, each iteration step costs about 55.9 s. After 7 iterations, we approach the convergent solution where both the relative errors of the frequency steps and the tuning gains satisfy the given specifications.
关键词： Constant tuning gain,Constant frequency step,Automatic synthesis,Iteration,Wideband voltage-controlled oscillator (VCO)
更新于2025-09-23 15:21:21
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Zinc Oxide Nanoparticles Synthesized by Suaeda japonica Makino and Their Photocatalytic Degradation of Methylene Blue
摘要： Green chemistry gained special attention for the environmental safety. In addition, green synthesized plant based nanoparticles for the degradation of industrial pollutant dye also received special focuses. Thus, photocatalytic activity of nanosized zinc oxide (Sj-ZnONps) synthesized by a simple co-precipitation method using sodium hydroxide, zinc nitrate, and Suaeda japonica extract as starting materials was carried out. The reaction was implemented in comparatively low temperature (50oC) without further calcination. The absorption spectrum demonstrated an extinction peak at ~362 nm, which is characteristic to the ZnO nanoparticles. Field-emission transmission electron microscope revealed smaller agglomeration of hexagonal Sj-ZnONps (~100 nm). X-ray diffraction patterns exposed polycrystalline ZnO with hexagonal wurtzite structure. The self-assembly of Sj-ZnONps was achieved due to the capping of phytoconstituents present in extract as evident from Fourier-transform infrared spectroscopy analysis. The photocatalytic degradation of Sj-ZnONps was estimated in reduction of methylene blue (MB). The reaction mixtures comprising of MB, S. japonica extract and Sj-ZnONps had the most significant decrease of MB by 54 %. In conclusion, the Sj-ZnONps can be used as a photocatalyst for decomposition of organic pollutions present in water.
关键词： Photocatalytic degradation,Green synthesis,Suaeda japonica Makino,Methylene blue,Zinc oxide nanoparticles
更新于2025-09-23 15:21:21
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Synthesis and Luminescence of Europium-Containing Compositions Based on Yttrium Oxide and Oxyfluorides
摘要： By heating the products isolated from an ethyl acetate medium, luminescent europium-containing compositions based on yttrium oxyfluorides and oxide have been synthesized. The concentration of Eu3+ ions in the compositions was from 0.10 to 10 at % of the yttrium content. It has been shown that the (EuхY1 – х)nOn – 1Fn + 2, (EuхY1 – х)OF, (EuхY1 – х)2O3, and (EuхY1 – х)5O4F7 phases are formed during the synthesis. The luminescence of the compositions is related to the 5D0 → 7Fj electron transitions of Eu3+ ions. It depends on the synthesis conditions, the type of matrix, the position of the Eu3+ ions in the crystal lattice, the excitation wavelength, and other factors.
关键词： europium,colloid synthesis,yttrium oxide,yttrium oxyfluorides,metal trifluoroacetates,luminescence,nonaqueous media
更新于2025-09-23 15:21:21
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Characterization and Formation Mechanism of the Nanodiamond Synthesized by A High Energy Arc-Plasma
摘要： A new fabrication strategy using thermal source of DC arc-discharge plasma is developed in the synthesis of nanodiamond particles. In the fabrication process, a solid mixture of Ni/Si/graphite coarse powders is used as the raw materials, meanwhile the gaseous mixture of H2/Ar served as the preparation atmosphere. The well-established arc-discharge plasma is significant in operation under a low gaseous pressure and an acceptable energy condition, and would be potential to become a novel process for synthesis of nanodiamond particles in large scale. The initially formed SiC clusters and the solid solution of Ni(C) particles are crucial in serving as crystal nuclei of diamond and an in situ carbon source which can gradually be released with cooling, respectively. Structural characterizations by high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), Raman spectra, and X-ray diffraction (XRD) confirm the existence nanodiamond particles, they are typically spherical with 5–20 nm in size. The formation of such nanodiamond particles by the arc-discharge thermal source is discussed in detail on the knowledge of binary phase diagram, constitution of raw materials, and nucleation/growth processes under the experimental conditions.
关键词： formation mechanism,synthesis,nanodiamond,DC arc-discharge plasma
更新于2025-09-23 15:21:21