Vanadium dioxide (VO2) has been a promising energy-saving material due to its reversible metal-insulator transition (MIT) performance. However, the application of VO2 films has been seriously restricted due to the intrinsic low solar-energy modulation ability (ΔTsol) and low luminous transmittance (Tlum) of VO2. In order to solve the problems, the surface structure of VO2 particles was regulated by the quenching process and the VO2 dispersed films were fabricated by spin coating. Characterizations showed that the VO2 particles quenched in deionized water or ethanolreserved VO2(M) phase structure and they were accompanied by surface lattice distortion compared to the pristine VO2. Such distortion structure contributed to less aggregation and highly individual dispersion of the quenched particles in nanocomposite films. The corresponding film of VO2 quenched in water exhibited much higher ΔTsol with an increment of 42.5% from 8.8% of the original VO2 film, because of the significant localized surface plasmon resonance (LSPR) effect. The film fabricated from the VO2 quenched in ethanol presented enhanced thermochromic properties with 15.2% of ΔTsol and 62.5% of Tlum. It was found that the excellent Tlum resulted from the highly uniform dispersion state of the quenched VO2 nanoparticles. In summary, the study provided a facile way to fabricate well-dispersed VO2 nanocomposite films and to facilitate the industrialization development of VO2 thermochromic films in the smart window field.
Highly ordered single-crystal iron nanowire arrays with different diameters have been fabricated in anodic aluminum oxide (AAO) templates by DC electrodeposition method. The Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) show that the iron nanowires are highly uniform and exhibit a single crystal structure. The X-ray diffraction (XRD) patterns of iron nanowire arrays indicate that most of the iron nanowire arrays have the obvious preferred orientation along the [200] direction. From the hysteresis loops of the iron nanowires, it reveals that the easy magnetization axes of nanowire arrays are along the long axis. The sample with smaller diameter (d=35nm) has a high square ratio (up to 98%) and a high coercive filed (1265Oe) when the external magnetic field is applied along axis of the nanowires. When the diameter decreases, the square ratio and the coercive field increase due to the single-domain structure and the strong shape anisotropy in the smaller diameter nanowire arrays.
A simple and cheap method has been applied to synthesize single-crystal uniform ZnO tubes with high yield in a hydrothermal process using Zn(NO3)2⋅6H2O and methenamine as reaction precursors at low temperature. The products are characterized by XRD, SEM, TEM and SAED. ZnO tubes are uniform single-crystal structures and grow along the [0001] direction. They have straight and regular hexagonal configuration with faceted ends and slippery side surfaces. The growth mechanism of ZnO tubes is investigated and the processing conditions are critical for the formation of ZnO tubes.
Highly oriented plate-like rod/tube arrays of ZnO are synthesized by a solution-based approach at low temperature. The ZnO rod/tube arrays grow oriented vertically on silicon substrate and the intersectant ZnO nanosheets stand on the backbones of ZnO rods/tubes. The constructions of plate-like rod or tube arrays depend on the processing conditions. The growth mechanisms are investigated based on the nucleation and growth process. The initial ZnO film formed on substrate is crucial for the growth of ZnO rods/tubes perpendicular to the substrate. The nanosheets grow around the ZnO rods/tubes by the secondary nucleation and growth process. The ZnO tubes are formed by the etching of the ZnO polar faces. The novel ZnO structures are expected to have great potential for electronics, photoelectronics, sensors, and catalysis etc.
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