No abstract

Spatially resolved dynamically reconfigurable control of thermal emission has comprehensive implications for fundamental science and technological applications, such as thermal camouflage and adaptive radiative heating/cooling. Materials and systems that can spatially control thermal emission with dynamic reconfigurability, simple manufacturability, and a large dynamic range have not been explored, so far. Here, a spatially resolved thermal emission control platform consisting of three components (a material with phase transition hysteresis, a thermal photonic device with a field‐optimized planarized structure, and an optically controllable patterning system) is built and validated. This platform presents excellent merits such as spatially resolved control of thermal emission, multilevel (up to nine levels) emission control with a large dynamic range of the emissivity modulation (0.19 for the insulating phase and 0.91 for the metallic phase) over a broad bandwidth (8–14 µm), and robust reconfigurability. The results demonstrate potential applications in the field of thermal photonics for information and energy harvesting.

In the pursuit of energy efficient materials, vanadium dioxide (VO) based smart coatings have gained much attention in recent years. For smart window applications, VO thin films should be fabricated at low temperature to reduce the cost in commercial fabrication and solve compatibility problems. Meanwhile, thermochromic performance with high luminous transmittance and solar modulation ability, as well as effective UV shielding function has become the most important developing strategy for ideal smart windows. In this work, facile CrO/VO bilayer coatings on quartz glasses were designed and fabricated by magnetron sputtering at low temperatures ranging from 250 to 350 °C as compared with typical high growth temperatures (>450 °C). The bottom CrO layer not only provides a structural template for the growth of VO (R), but also serves as an antireflection layer for improving the luminous transmittance. It was found that the deposition of CrO layer resulted in a dramatic enhancement of the solar modulation ability (56.4%) and improvement of luminous transmittance (26.4%) when compared to single-layer VO coating. According to optical measurements, the CrO/VO bilayer structure exhibits excellent optical performances with an enhanced solar modulation ability (ΔT = 12.2%) and a high luminous transmittance (T = 46.0%), which makes a good balance between ΔT and T for smart windows applications. As for UV-shielding properties, more than 95.8% UV radiation (250-400 nm) can be blocked out by the CrO/VO structure. In addition, the visualized energy-efficient effect was modeled by heating a beaker of water using infrared imaging method with/without a CrO/VO coating glass.

A novel thermochromic WO3/VO2/WO3 sandwich structure was deliberately designed and deposited by a reactive magnetron sputtering technique.

The PTFE (Teflon) has been selected as the self-template structural material in preparation of VO2 films using reactive magnetron sputtering systems and post annealing progress. Spontaneous random nano-porous structures of VO2 films growing on quartz glasses have been deliberately established via bottom-up processing through this novel and facile approach. The nano-porous VO2 films exhibit an excellent optical performance based on localized surface plasmon resonance (LSPR), with ultrahigh luminous transmittance (Tlum) up to 78.0% and the promoted solar modulation ability (ΔTsol) of 14.1%. Meanwhile, the ingenious microstructure of film provides an antireflection function from multiple perspectives in visible light, with the potential of the windshield on vehicles for smart solar modulation. The nano-porous films expand the practical application of thermochromic VO2 to a fire-new field, breaking the optical performance envelope of single-layer dense VO2 film away, and offering a universal method to prepare homogeneous nano-porous structures for thin films. IntroductionIntelligent windows, or smart windows, can automatically manage the heat by modulating the amount of solar radiation (especially the near-infrared region) in response to environmental temperature variations, exhibit potential application in building energy-saving and temperature control. 1-3 Among diverse thermochromic materials, vanadium dioxide (VO2) was regarded as the representative candidate due to the reversible phase change from an infrared-transmitted semiconductor-state (VO2(M)) to infrared-reflective metal-state (VO2(R)) when below/over the critical transition temperature (~340K), while nearly maintains the transmittance in luminous range. 4, 5 Therefore, VO2 films can be capable to impede unnecessary heat at high temperature while allow the incident solar radiation into indoors automatically, displays an ideal performance for energy savings. 6, 7 However, the relatively high phase transition temperature should be decreased to meet the requirement.Fortunately, bringing in high valence dopants like tungsten can provide an efficiently approach to reduce intrinsic transition temperature (~68°C) of VO2 by modifying the electronic density of states. 8,9 Nevertheless, some other drawbacks, such as the low luminous transmittance (Tlum) with unsatisfied solar modulation ability (ΔTsol) as well as the native dark brown color of films have still obstructed the actual use of VO2-based smart windows. 10, 11 Here, the low luminous transmittance and the native dark brown color of films were probably caused by small optical band gap of VO2, which gives rise to absorption in short-wavelength range. 12, 13 A large number of methods have been employed to enhance the optical performance (Tlum and ΔTsol) of VO2. Doping is also used here, dopants like Mg or F can increase Tlum but make a deterioration of ΔTsol. [14][15][16] In addition, antireflection layers such as TiO2, Cr2O3, WO3, have been introduced to enhance both Tlum (40-55%) and ΔTsol simultaneously ba...

Long-term stability is a great challenge for commercializing VO 2 film, but corresponding research is lacking. This work demonstrated that the cross-section of VO 2 films is important to the corresponding deterioration process. An encapsulation structure is designed to protect VO 2 films from deterioration by utilizing stable and naturally hydrophobic HfO 2 layers. The proposed structure shows greatly extended service life, which could be equal to 16 years in the real environment. It provides a new strategy for stable VO 2 films in commercialization of applications.

No abstract

No abstract