Two-dimensional (2D) photonic structures, widely used for generating photonic band gaps (PBG) in a variety of materials, are for the first time integrated with the temperature-dependent phase change of vanadium dioxide (VO). VO possesses thermochromic properties, whose potential remains unrealized due to an undesirable yellow-brown color. Here, a SiO/VO core/shell 2D photonic crystal is demonstrated to exhibit static visible light tunability and dynamic near-infrared (NIR) modulation. Three-dimensional (3D) finite difference time domain (FDTD) simulations predict that the transmittance can be tuned across the visible spectrum, while maintaining good solar regulation efficiency (ΔT = 11.0%) and high solar transmittance (T = 49.6%). Experiments show that the color changes of VO films are accompanied by NIR modulation. This work presents a novel way to manipulate VO photonic structures to modulate light transmission as a function of wavelength at different temperatures.

This study presents a novel approach towards achieving high luminous transmittance (T(lum)) for vanadium dioxide (VO(2)) thermochromic nanogrid films whilst maintaining the solar modulation ability (ΔT(sol)). The perforated VO(2)-based films employ orderly-patterned nano-holes, which are able to favorably transmit visible light dramatically but retain large near-infrared modulation, thereby enhancing ΔT(sol). Numerical optimizations using parameter search algorithms have implemented through a series of Finite Difference Time Domain (FDTD) simulations by varying film thickness, cell periodicity, grid dimensions and variations of grid arrangement. The best performing results of T(lum) (76.5%) and ΔT(sol) (14.0%) are comparable, if not superior, to the results calculated from nanothermochromism, nanoporosity and biomimic nanostructuring. It opens up a new approach for thermochromic smart window applications.

We demonstrate a reflection-type sensor in the midinfrared spectra based on resonant excitation of surface phonon polaritons (SPhPs). In this range, SPhPs are characterized by the high density of states associated with slow surface waves that lead to enhanced resonance absorption. Delocalized SPhPs were excited by irradiating TM-polarized light on a one-dimensional grating embedded in a SiC substrate. The sensor response was characterized by changing the refractive index (RI) of a lossless CO2 gas. A detection limit of 2×10−5 RI units was obtained at a wavelength of 11.9 μm.

Surface patterning is a popular approach to produce photonic metasurfaces that are tunable when electro-optic, thermooptic, or magneto-optic materials are used. Vanadium oxides (V y O x ) are well-known phase change materials with many applications, especially when used as tunable metamaterial photonic structures. Particularly, VO 2 is a well-known thermochromic material for its near-room-temperature phase transition from the insulating to the metallic state. One-dimensional (1D) VO 2 nanograting structures are studied by numerical simulation, and the simulation results reveal that the VO 2 nanograting structures could enhance the luminous transmittance (T lum ) compared with a pristine flat VO 2 surface. It is worth mentioning that T lum is also polarization-dependent, and both larger grating height and smaller grating periodicity give enhanced T lum , particularly at TE polarization in both insulating (20 °C) and metallic (90 °C) states of VO 2 . Femtosecond laser-patterned VO 2 films exhibiting nanograting structures with an average periodicity of ≈500−700 nm have been fabricated for the first time to enhance thermochromic properties. Using X-ray photoelectron spectroscopy, it is shown that at the optimum laser processing conditions, VO 2 dominates the film composition, while under extra processing, the existence of other vanadium oxide phases such as V 2 O 3 and V 2 O 5 increases. Such structures show enhanced transmittance in the near-infrared (NIR) region, with an improvement in NIR and solar modulation abilities (ΔT NIR = 10.8%, ΔT sol = 10.9%) compared with a flat VO 2 thin film (ΔT NIR = 8%, ΔT sol = 10.2%). The slight reduction in transmittance in the visible region is potentially due to the scattering caused by the imperfect nanograting structures. This new patterning approach helps understand the polarization-dependent optical response of VO 2 thin films and opens a new gateway for smart devices.

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