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VO2 microrods synthesized from V2O5 thin films
摘要： Self-assembled single crystal VO2 microrods (MRs) with a length up to 600 μm have been synthesized on Si and sapphire substrates by the annealing of V2O5 thin films. The nucleation and growth of VO2 MRs from V2O5 thin films were investigated. The morphology and microstructure evolutions of the intermediate phases during the reduction process were characterized by SEM, HRTEM, XPEEM, and Raman spectroscopy. The results have shown that the conversion of V2O5 thin films to VO2 MRs is dominated by a melting-nucleation-growth mechanism. The growth of VO2 MRs can be controlled by V2O5 melting process and a consistent feeding of V2O5 liquids to the growing VO2 MR would lead to ultra-long VO2 MRs. Further, epitaxial growth of VO2 MRs can be induced by using an r-cut sapphire substrate.
关键词： Growth mechanism,Reduction,V2O5 thin films,VO2 microrods,Epitaxial growth
更新于2025-09-23 15:23:52
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ZnO Micro- and Nanostructures Obtained by Thermal Oxidation: Microstructure, Morphogenesis, Optical, and Photoluminescence Properties
摘要： ZnO micro- and nanostructures were obtained through thermal oxidation of Zn powders at high temperature under air atmosphere. A detailed study of the microstructure, morphology, optical, and photoluminescence properties of the generated products at different stages of thermal oxidation is presented. It was found that the exposure time has a strong influence on the resulting morphology. The morphogenesis of the different ZnO structures is discussed, and experimental parameters for fabricating ZnO tetrapods, hollow, core-shell, elongated, or rounded structures by thermal oxidation method are proposed on the basis on the obtained results. Notoriously, the crystal lattice of the ZnO structures has negligible residual strain, although, the density of point defects increases when the thermal treatment is extended; as consequence, their visible luminescence upon UV excitation enhances.
关键词： growth mechanism,ZnO structures,thermal oxidation,physical properties
更新于2025-09-23 15:23:52
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A novel growth strategy of TiO<sub>2</sub> anodic films using surface residual stress as driving force
摘要： The relationship between residual stress and growth behavior of anodic titanium oxide films (TiO2) was investigated in terms of defect chemistry and the nanocrystalline materials thermodynamic. The results showed that the surface residual stress can be controlled by acting on the duration of the surface mechanical attrition treatment (SMAT). When samples are processed by grinding for 30 min, the residual stress value reaches a maximum of 73.13 MPa, approximately 7.2 times higher than the one obtained with untreated sample. Under these conditions, the thickness of the anodic film was about 1200 nm, three times that of the TA2 anodic film. Furthermore, the results of electrochemical tests showed that following the surface mechanical attrition treatment, the anodic film show lower density vacancies, higher resistance to the diffusion of Cl-, higher density, and an improved corrosion resistance when compared to TA2. Generally speaking, the growth behavior of the anodic film can be improved by identifying the suitable residual stress.
关键词： Surface mechanical attrition treatment,Anodic oxidation,Corrosion resistance,Growth mechanism
更新于2025-09-23 15:23:52
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Morphology Controllable Synthesis of Hierarchical WO3 Nanostructures and C2H2 Sensing Properties
摘要： In this paper, we reported the morphology controllable synthesis of hierarchical WO3 nanostructures, i.e. nanorods, nanospheres and nanoflowers, via a facile hydrothermal route. All the obtained WO3 nanostructures were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET), respectively. A possible growth mechanism for the three various nanomaterials was proposed in detail. WO3 based gas sensors were fabricated with the synthesized nanomaterials and the gas sensing performances to acetylene (C2H2), one of the fault characteristic gases dissolved in power transformer oil, were systematically measured. It was found that the sensor based on nanosheet-assembled nanoflowers with largest surface (56.74 m2g-1) exhibits the highest sensing performance including gas response (32.31) and response-recovery time (12 s, 17 s) to 200 ppm C2H2. The results indicate that WO3 sensing materials could be a promising choice for synthesizing high-performance C2H2 sensors for the judgement of the early latent faults of the oil immersed transformer.
关键词： Hierarchical WO3,Gas sensors,Growth mechanism,C2H2 sensing performances
更新于2025-09-23 15:22:29
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Catalytic synthesis of SiC nanowires in an open system
摘要： SiC nanowires (NWs) are usually synthesized in a closed vacuum reaction system which limits the yield of SiC NWs. In this work, SiC NWs and carbon nanotubes were synthesized in an open tube furnace at 1550 ℃ with Si powder as silicon sources, ethanol as carbon sources and ferrocene as catalyst. The as-synthesized products were ultralong β-SiC NWs with the diameter about 80-100 nm and the length up to several tens micrometers. The diameter of the carbon nanotubes was about 20-30 nm. The carbon nanotube yarns about 20 cm in length were obtained at the end of the tube furnace. The growth mechanism of SiC NWs and carbon nanotubes were proposed. Compared with the traditional synthetic techniques in the high vacuum closed system, the novel synthesis method in the open system provided a new approach to the synthesis of SiC NWs.
关键词： Carbon nanotubes,SiC nanowires,Open reaction system,Growth mechanism
更新于2025-09-23 15:22:29
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New Insights Into the Growth Mechanism of Ultrathin Au Nanowires from Combined In-Situ EXAFS and SAXS Studies
摘要： The synthesis at room temperature of Au nanowires (NWs) in hexane solution of HAuCl4.3H2O, oleylamine and triisopropylsilane, was “in-situ” monitored by means of X-ray Absorption Fine Structure Spectroscopies and Small Angle X-Ray Scattering to determine, under identical synthesis conditions, both the changes of the oxidation state of gold atoms and the evolution of the size and shape of the objects involved in the formation of Au NWs. We propose a multi-stage process for the formation of the NWs: first, Au(III) atoms form a planar-square geometry complex that is continuously reduced to give Au(I) disc-like structures with diameters bigger than that of the final NWs. In a second stage, characteristic length/thickness ratio of these disc-like objects increases to form cylinders, presumably by aurophilic interactions between Au(I) centers and stacking of the discs. When most of the Au atoms have been reduced to Au(I), the reduction to Au(0) begins (third stage) and the NWs grow forming an hexagonal arrangement, separated by a bilayer of oleylamine molecules (fourth stage). Finally, a slow reduction leads the reaction to the final product, formed by bundles of long, ultrathin Au NWs.
关键词： triisopropylsilane,in-situ EXAFS,growth mechanism,SAXS,Au nanowires,oleylamine
更新于2025-09-23 15:21:21
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Dependence of h-BN film thickness as grown on nickel single crystal substrates of different orientation
摘要： Chemical vapor deposition of 2D materials has been an active area of research in recent years because it is a scalable process for obtaining thin films that can be used to fabricate devices. The growth mechanism for hexagonal boron nitride (h-BN) on metal catalyst substrates has been described to be either surface energy driven or diffusion driven. In this work, h-BN is grown in a CVD system on Ni single crystal substrates as a function of Ni crystallographic orientation to clarify the competing forces acting on the growth mechanism. We observed that the thickness of the h-BN film depends on the Ni substrate orientation, with the growth rate increasing from the (100) surface to the (111) surface, and the highest on the (110) surface. We associate the observed results with surface reactivity and diffusivity differences for different Ni orientations. Boron and nitrogen diffuse and precipitate from the Ni bulk to form thin multilayer h-BN. Our results serve to clarify the h-BN CVD growth mechanism which has been previously ascribed to a surface energy-driven growth mechanism.
关键词： surface diffusion,electron backscatter diffraction,growth mechanism,hexagonal boron nitride
更新于2025-09-23 15:21:01
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Growth mechanism of porous 3Ca??SiC films prepared via laser chemical vapor deposition
摘要： Porous SiC film is an excellent electrode material for robust micro-supercapacitors used in extremely harsh environments. In one of our previous studies, porous 3C–SiC film with high areal capacitance and high deposition rate was prepared via laser chemical vapor deposition (LCVD). However, it is still urgent to explore the formation mechanism of porous structures using LCVD. In this study, the microstructure of the porous cubic SiC film prepared via LCVD was analyzed in detail using scanning and transmission electron microscopy techniques. The growth mechanism of the deposits has been proposed according to the “growth competing theory” and “shadow effect theory.”
关键词： Growth mechanism,Porous 3C–SiC film,Microstructure,Laser chemical vapor deposition (LCVD)
更新于2025-09-23 15:19:57
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Metallic indium segregation control of InN thin films grown on Si(1?0?0) by plasma-enhanced atomic layer deposition
摘要： InN thin films were grown on Si(1 0 0) substrates by plasma-enhanced atomic layer deposition (PEALD). In this work, It is found that the island growth of InN on Si(1 0 0) easily happens at the initial PEALD period. The PEALD parameters have been systematically investigated to optimize the size, density, coalescence and distribution uniformity of InN grains with good crystallinity and no metallic indium clustering. Especially, indium segregation of PEALD-grown InN has a direct dependence on the deposition temperature (T), the supply of tri-methylindium (TMIn) precursor and nitrogen plasma (NP) source. Based on our proposed PEALD mechanism of InN, a polycrystalline hexagonal InN thin film in the thickness of 24.2 nm has been well deposited at the growth per cycle (GPC) of 0.8 ?/cycle. And it shows a (0 0 2) preferential orientation and no any structural phase of metallic indium segregation. As a result, it may provide a useful guide for deeply understanding the PEALD growth mechanism of InN and In-rich nitrides, which further extends the promising applications in high-efficiency photovoltaics and high speed electronic devices.
关键词： Indium segregation,PEALD,Growth mechanism,InN,Polycrystalline
更新于2025-09-23 15:19:57
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Thermal Shock Synthesis of Metal Nanoclusters within On-the-fly Graphene Particles
摘要： Metal nanoclusters (1-10 nm) have drawn great attention due to their potential applications including energy storage, catalysis, nanomedicine and electronic devices. However, manufacturing ultra-small metal nanoparticles at high concentrations in an unaggregated state is not a solved problem. Here we report an aerosol-based thermal shock technique for in situ synthesis of well-dispersed metal nanoclusters in on-the-fly graphene aerosols. A rapid thermal shock to the graphene aerosol has been used to nucleate and grow the metal nanoclusters with subsequent quenching to freeze the newly formed nanoclusters in the graphene aerosol matrix. A characteristic time analysis comparison with experiment shows that the nanocluster formation is governed by nucleation and subsequent surface growth, and that the graphene retards coagulation, enabling unaggregrated metal nanoclusters. The method is generic, and we show the formation of sub-10 nm Ni, Co and Sn nanoclusters. This continuous aerosol-based thermal shock technique offers considerable potential for the scalable synthesis of well-dispersed and uniform metal nanoclusters stabilized within a host matrix. As an example of potential application, we demonstrate very favorable catalytic properties.
关键词： thermodynamics,in situ growth,growth mechanism,thermal shock synthesis,kinetics,metal nanoclusters
更新于2025-09-19 17:15:36