Fluorine doped vanadium dioxide thin films for smart windows

Thermochromic fluorine doped thin films of vanadium dioxide were deposited from the aerosol assisted chemical vapour deposition reaction of vanadyl acetylacetonate, ethanol and trifluoroacetic acid on glass substrates. The films were characterised with scanning electron microscopy, variable temperature Raman spectroscopy and variable temperature UV/Vis spectroscopy. The incorporation of fluorine in the films led to an increase in the visible transmittance of the films whilst retaining the thermochromic properties. This approach shows promise for improving the aesthetic properties of vanadium dioxide thin films.     

对硝基苯甲醛缩对氨基乙酰苯胺希夫碱的室温固相合成及其可逆热致变色研究

以对硝基苯甲醛和对氨基乙酰苯胺为原料,通过室温固相反应合成了一种希夫碱衍生物,用元素分析、核磁共振等方法对产物进行了表征,并利用DSC技术对其变色过程进行了研究。结果表明,采用室温固相反应的方法合成的化合物结构和目标产物一致,且产率较高,熔程较短,纯度较高,反应效果理想。标题化合物作为热致变色材料具有变色敏锐、颜色对比明显、可逆性好以及变色温度高等特点,是一种具有良好应用前景的可逆热致变色材料。     

基于Au/VO2纳米结构的可调控红外吸收器设计

设计了一种Au/VO_2周期性方形孔洞阵列结构的红外吸收器,利用时域有限差分法研究了吸收器的结构参数对吸收光谱的影响,优选出VO_2和Au膜层厚度分别为140 nm和80 nm,孔洞边长和阵列周期分别为1.1μm和1.2μm时,吸收可调控特性最为明显,在2.3μm处其高低温的吸收率差值可达80.3%.理论模拟计算了光以不同偏振、入射角入射时的吸收,结果表明,正入射时吸收器是偏振无关的;斜入射时吸收器具有广角吸收的特点,与TM偏振相比TE偏振下吸收器具有更强的角度依赖性.低温时吸收器中的电磁场呈高度局域化分布,表现为强的吸收;而高温时吸收器中的电磁场分布在吸收器表面,吸收被抑制.所设计的吸收器吸收效率高,吸收强度可以调控,可应用于新型可调控智能光电器件.     

Solvent and Temperature Effects on Spectral Properties of Two Poly(32alkyl)thiophene Derivatives

Two alkyl substituted polythiophene derivatives: poly(32hexylthiophene)(P3HT) and poly(32decylthiophene)(P3DT), have synthesized by oxidation coupling polymerization of 32alkylthiophene using iron (III) chloride as catalyst in chloroform. While both polymers in pure chloroform solution have maximum absorption at approximately same wavelength of 440 nm, they behave differently with respect to changes observed on their UV2visible and photoluminescence spectra when the quality of the poor solvent is changed in good solvent (chloroform) / poor solvent (methanol) mixtures. With increasing volume fraction of methanol in mixtures, the absorption spectra of P3HT and P3DT red2shift, peaking at maximum wavelength of 495 nm (P3HT) and 510 nm(P3DT). Furthermore, the absorption spectra of the two polymers in chloroform blue2shift as the temperature rises. P3HT shows 4.73 nm blue2shifts at 50℃in contrast to the case at 20℃, while P3DT blue2shifts about 5.04 nm. The photoluminescence spectra of the two polymers in mixed solution are also investigated, which show that the luminescence spectra shift to longer wavelength with an accompanying drop in the PL intensity as methanol is increased. The absorption and emission spectra of the two polymers in a poor solvent and a thin film are similar, which indicate that a similar longer conjugation length in the two cases. It could conclude that the polymers exist almost the same conformations and aggregations in both a poor solvent and a thin film. P3DT exhibits more sensitive spectra properties (big red2shifts in both absorption and luminescence spectra in poor solvents and large blue2shifts at high temperature) with contrast to P3HT, which imply that long side alkyl may improve the chromic properties of the polymer.     

Evidence of different oxygen states during thermal coloration of tungsten oxide

In this study, we report on the thermal reduction of tungsten oxide studied with in situ photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). XPS measurements of the O1s core level of the annealed oxide film in vacuum show the appearance of a second state displaced in 1.1 eV towards higher binding energy. We propose that the shifted component is due to the difference in the charge state of oxygen anions and results from oxygen that is not bonded to metal. Simultaneous increase of the O¹⁶ ion yield measured with ToF-SIMS suggests that this higher binding energy component is related to atomic oxygen that is released from the oxide but remains in film.     

Control of thermochromic spectrum in vanadium dioxide by amorphous silicon suboxide layer

Vanadium dioxide (VO₂) is a promising candidate for various thermochromic devices. Layering VO₂ film with amorphous silicon suboxide (a-SiO_x) is an effective approach for controlling the thermochromic spectrum efficiently, since a-SiO_x possesses an easily adjustable refractive index over a wide range. However, the crystalline quality of VO₂ is so sensitive to under- and/or over-coated materials that the a-SiO_x coatings may be disadvantageous with respect to material suitability. In this study, the controllability of the thermochromic spectrum of VO₂ by employing a-SiO_x layer was evaluated under several fabrication conditions and, as a result, it was found that an a-SiO_x layer can control thermochromism well without any decline in the stability of VO₂ crystalline growth, which strongly suggests the possibility of expansion in the optical design for efficient thermochromic control.     

The solution and solid-state thermochromism of unsymmetrically substituted polysilanes

The thermochromic behavior of a number of dialkyl-substituted polysilanes has been studied in some detail. The formation of a long wavelength-absorbing species in solution at low temperatures is dependent on the polymer structure. Evidence for polymer aggregation has been found in solutions as dilute as 10^–5 M (based on the monomer unit). Fluorescence emission studies at very low concentrations (<10^–6 M) suggest that single-molecule events can result in the observed thermochromic changes. We have obtained no evidence for the proposed coil-to-rod transition at low temperature by either light or neutron scattering; indeed the scattering studies seem to suggest that the polymer coil dimensions actually shrink slightly prior to the onset of aggregation. It is proposed that the thermochromism observed for many dialkyl polysilanes in solution is initiated by the formation of extended segments within a polymer chain which are long enough to stabilize intra- and intersegmental interactions. In extremely dilute solutions this interaction results in a shrinkage of a single polymer chain; at higher concentrations the interaction results in aggregation.This paper was presented at the Second International Topical Workshop, Advance in Silicon-Based Polymer Science.     

Advances in chromogenic materials and devices

Chromogenic materials allow the transmittance of visible light and solar energy to be varied under the action of an external stimulus. This paper first discusses buildings related energy savings that can be accomplished by chromogenic technologies, and their beneficial effects on comfort issues. We then summarize recent work on thermochromic VO₂-based thin films with particular attention to multi-layers of VO₂ and TiO₂ and to new VO₂:Mg films for which the doping gives significantly lowered absorption of visible light. The final part covers electrochromic materials and devices with foci on coloration efficiency and on durability issues for foil-type constructions based on films of WO₃ and NiO.