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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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Diastereoisomer-Induced Morphology Tunable Self-Assembled Organic Microcrystals of Conjugated Molecules for Ultraviolet Laser
摘要： Precisely controlling self-assembly behavior and micro/nanostructure morphology of conjugated materials is significant for constructing optoelectronic devices. Inspired by natural functional materials, molecular stereoisomerism strategy (MSS) is an effective and convenient means to tune their molecular arrangement and macroscopic property of conjugated materials. Herein, a supramolecular chiral difluorenols, 9,9′-diphenyl-9H,9′H-[2,2′-bifluorene]-9,9′-diol (DPFOH), is set as a desirable model to reveal the diastereomeric effects of conjugated molecules toward controlling the micro/nanostructure morphology and optoelectronic behavior for deep-blue organic laser. Two diastereomers, raceme (rac)- and mesomer (meso)-DPFOH, are obtained and unambiguously elucidated by X-ray crystallography. It is common sense to observe the slight diastereomeric effects on photophysical properties and electrochemical characteristics in solution or pristine film state for the isotropic phase. Interestingly, as a consequent of the disparate multi-dimensional intermolecular interaction, rac-DPFOH molecule can self-assemble into 1D rod-shaped but rectangular plate-shaped microcrystals for meso-DPFOH. Impressively, rac-DPFOH microrod presents a well-defined emission with an excellent ultraviolet microlasing behavior at 398 nm, whereas the 2D microplate of meso-DPFOH show a broad emission centered at 420 nm without gain processing. Therefore, MSS provides a new approach to design conjugated molecules and tune superstructure morphology for optoelectronic applications.
关键词： optical properties,tunable morphology,organic ultraviolet microlasers,diastereoisomer effect,microcrystals
更新于2025-09-23 15:21:01
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A Study of the Structural Organization of Water and Aqueous Solutions by Means of Optical Microscopy
摘要： The structural organization of water and aqueous solutions under an optical microscope in a layer with a thickness of 8 μm was investigated. It is shown that under room conditions water (including “ultrapure” water) and aqueous solutions are microdispersed systems. The revealed effect does not depend on the properties of the substrate (texture, hydrophilicity/hydrophobicity) and is an inherent property of the liquid. The disperse phase is based on contrasting micron-sized formations located in the center of low-contrast homogeneous spheres observed in a layer with a thickness of the order of the diameter of the observed structures. They form loose millimeter-sized associates in the liquid phase. When the water is boiled, the associates become disordered, but the dispersed phase is preserved. An increase in the ionic strength of the solution is accompanied by coacervation of the dispersed phase. When the liquid part of the water evaporates, the microdispersed phase remains on the substrate. The central particles begin to grow and take on the form of crystals. On the basis of the literature data and their own research, the authors believe that the structures are sodium chloride microcrystals surrounded by a thick layer of hydrated water. Possible ways of salt penetration into the aquatic environment are discussed.
关键词： hydrated shells,water-salt units,microstructure of liquids,coacervates,salt microcrystals,self-assembly,air pollution
更新于2025-09-19 17:15:36
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Mixed-dimensional self-assembly organica??inorganic perovskite microcrystals for stable and efficient photodetectors
摘要： The unstability of organic-inorganic perovskites in humid air is a serious bottleneck that restricts their practical applications in optoelectronics, although tremendous achievements have been scored in organic-inorganic perovskite devices. Materials engineering is believed to be one of the most direct strategy to address this issue. Mixed-dimensional organic-inorganic perovskite microcrystals, which have the advantage of relatively good charge carrier transport owing to limited grain boundaries and low defect densities compared to perovskite thin films, integrate the good humidity stability of two-dimensional (2D) and single-phase quasi-2D perovskites and the high photoresponse of 3D perovskites in an individual crystal, rendering them an excellent candidate for the development of high-performance photodetectors. Herein, the (C6H5CH2CH2NH3, PEA)2(CH3NH3, MA)n-1PbnBr3n+1 (n = 1, 3, 5, ∞ ) perovskite microcrystals have been synthesized using an anti-solvent vapor-assisted method, and the optoelectronic properties of these microcrystals are investigated by fabricating photodetectors in a lateral configuration. The (PEA)2(MA)2Pb3Br10 and (PEA)2(MA)4Pb5Br16 perovskites are proved to be mixed-dimensional microcrystals, respectively, which consist of the single phases of 2D (PEA)2PbBr4, quasi-2D perovskite, and 3D MAPbBr3. The photodetectors based on the individual (PEA)2(MA)2Pb3Br10 and (PEA)2(MA)4Pb5Br16 perovskite microcrystals show better performances than the (PEA)2PbBr4 microcrystal photodetector, and exhibit higher humidity resistance than the MAPbBr3 device. The best performances are achieved in the (PEA)2(MA)4Pb5Br16 microcrystal photodetector with a high responsivity of 182.63A/W, detectivity of 2.51×1014 Jones, and gain of 5.58×102, which can detect an optical signal with an extremely low light power density of 2.47 nW/cm2. Our results demonstrate that developing mixed-dimensional perovskite microcrystals is a promising way to construct highly efficient and stable photodetectors.
关键词： organic-inorganic perovskites,stable and efficient photodetectors,mixed-dimensional microcrystals,humidity stability
更新于2025-09-19 17:13:59
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Electrically controlled growths of 4-N,N-dimethylamino-4a?2-Na?2-methyl-stilbazolium tosylate (DAST) organic microcrystals
摘要： 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) is one of the most important organic nonlinear optical (NLO) materials, but its controlled growth remains a challenge. Herein, we describe a novel method to control the growth of DAST on the surfaces of indium tin oxides coated with the patterned photoresists by electric field. Results indicate that zero-dimensional (0D) spherical DAST microcrystals tend to grow along the photoresist lines if an electric field with a low frequency of 500 Hz is applied. Rather differently, one-dimensional (1D) DAST microwires preferentially grow along the gaps of the photoresist lines under the control of an electric field with a high frequency of 1000 Hz. Growth of DAST microcrystals controlled by electric field leads to the increase in the crystallinity, but the chemical structures remain unchanged. Moreover, second harmonic generation signal was measured from the as-grown DAST microcrystals. The results presented in this work are helpful for rationally controlling the growth of 0D or 1D DAST microcrystals, and particularly, the strategy can be further expanded to control the growth of DAST derivatives or other organic NLO materials with similar chemical structures.
关键词： Spectral analyses,Growth mechanism,Electric field induction,DAST microcrystals,Nonlinear optical material
更新于2025-09-16 10:30:52
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UV Luminescence and Lasing in Ensembles of Zinc-Oxide Microcrystals with Copper
摘要： Microrod arrays of zinc oxide with copper have been grown by chemical vapor deposition on single-crystal sapphire substrates preliminarily covered with a nanoscale copper layer. The presence of copper (about 0.3%) in zinc-oxide microrods has been experimentally shown to increase the photoluminescence intensity of the ZnO microcrystal arrays, reduce the lasing threshold, and lead to a small (by ~2.5 nm) blue shift of the radiation intensity peak of the ZnO microcrystals. It is shown that the laser-radiation character depends on the morphology of the ZnO microrod arrays.
关键词： lasing,zinc-oxide microcrystals,UV luminescence,copper doping,chemical vapor deposition
更新于2025-09-09 09:28:46