High performance metasurfaces for thermal radiative cooling applications can be identified using computational optimization methods. This work has identified an easy-to-fabricate temperature phase transition VO2 nanowire array laid atop dielectric BaF2 Fabry-Perot cavity-on-metal with total coating thickness of 2 um. This optimized structure has ability to self-adaptively switch between high reflectance at low temperature to high emissivity at high temperature in the broad thermal infrared spectrum. This design demonstrates exceptional turn-down figure-of-merit compared to previously realized configurations utilizing VO2 metasurfaces and multilayers. The mechanism is achieved with a sub-wavelength nanowire array effective medium that switches between anti-reflecting gradient coating and Fabry-Perot interference. This thin metasurface coating could impact self-cooling of the solar cells, batteries, and electrical devices where risk presents at high temperatures.
We present an electro-optic modulator exploiting an array of Vanadium dioxide nanorods operating in the epsilon near regime as the active switching material integrated in a silicon waveguide. The modulator takes advantage of the insulator-to-metal transition of Vanadium dioxide to achieve a robust modulation depth of 19.7 dB/micron with a broad wavelength of operation. Using simulations, we demonstrate how the effective permittivity of the metamaterial can be tuned to a near-zero value by varying the nanorod geometry. The paper also proposes a novel hexagonal array design which achieves low in…
We demonstrate the broadband operation of a switchable terahertz quarter-wave plate achieved with an active metasurface employing vanadium dioxide. For this purpose, we utilize anisotropically deformed checkerboard structures, which present broadband characteristics compatible with deep modulation. Moreover, the metasurface is integrated with a current injection circuit to achieve state switching; this injection circuit can also be employed to monitor the electric state of vanadium dioxide. We estimate the Stokes parameters derived from the experimental transmission spectra of the fabricated m…
We present a plasmonic modulator based on hybrid orthogonal silver junctions using vanadium dioxide as the modulating material on the silicon on insulator. The modulator has an ultra-compact footprint of 1.8μm x 1μm with a 100nm x 100nm modulating section based on the orthogonal geometry. We take advantage of large change in the refractive index of vanadium dioxide during its phase transition to achieve a high modulation depth of 46.89dB/μm. We also provide a fabrication strategy for the development of this device. The device geometry has potential applications in the development of next gener…
We present an experimental demonstration of passive, dynamic thermal regulation in a solid-state system with temperature-dependent thermal emissivity switching. We achieve this effect using a multilayered device, comprised of a vanadium dioxide (VO2) thin film on a silicon substrate with a gold back reflector. We experimentally characterize the optical properties of the VO2 film and use the results to optimize device design. Using a calibrated, transient calorimetry experiment we directly measure the temperature fluctuations arising from a time-varying heat load. Under laboratory conditions, w…
A limiting optical diode is an asymmetric nonlinear device that is bidirectionally transparent at low power, but becomes opaque when illuminated by sufficiently intense light incident from a particular direction. We explore the use of a phase-transition material, vanadium dioxide (VO2), as an active element of limiting optical diodes. The VO2 phase transition can be triggered by optical absorption, resulting in a change in refractive index orders of magnitude larger than what can be achieved with conventional nonlinearities. As a result, a limiting optical diode based on incident-direction-dep…
We conceptualized three-array scalable metasurfaces comprising only three thin strip grids and numerically demonstrated their characteristics in the mid-infrared spectral regime for switchable polarization manipulation and related asymmetric diodelike transmission (AT). A few or all of the grids were taken to be made of VO$_2$, a phase-change material. For each proposed metasurface, two effective structures and, therefore, two different functionalities exist, corresponding to the metallic and insulating phases of VO$_2$. The achieved scenarios of functionality switching that depend on the VO$_…
Resonant optical phased arrays are a promising way to reach fully reconfigurable metasurfaces in the optical and NIR regimes with low energy consumption, low footprint and high reliability. Continuously tunable resonant structures suffer from inherent drawbacks such as low phase range, amplitude-phase correlation or extreme sensitivity that makes precise control at the individual element level very challenging. In order to bypass these issues, we use 1-bit (binary) control for beam steering for an innovative nano-resonator antenna and explore the theoretical capabilities of such phased arrays.…
Dynamic radiative cooling with variable emissive power is experimentally demonstrated in this study by a wavelength-selective tunable metafilm emitter, which consists of an opaque aluminum film, a sputtered silicon spacer, and a thermochromic vanadium dioxide (VO2) layer fabricated by a furnace oxidation method. The temperature-dependent spectral emittance, experimentally obtained from spectral reflectance measurements, clearly shows a pronounced emission peak around 10 um wavelength when the VO2 experiences an insulator-to-metal phase transition near 65C. The tunable metafilm emitter achieves…
One route to create tunable metamaterials is through integration with "on-demand" dynamic quantum materials, such as vanadium dioxide (VO2). This enables new modalities to create high performance devices for historically challenging applications. Indeed, dynamic materials have often been integrated with metamaterials to imbue artificial structures with some degree of tunability. Conversely, metamaterials can be used to enhance and extend the natural tuning range of dynamic materials. Utilizing a complementary split ring resonator array deposited on a VO2 film, we demonstrate enhanced terahertz…
Abstract: An induced-transmission filter (ITF) uses an ultrathin layer of metal positioned at an electric-field node within a dielectric thin-film bandpass filter to select one transmission band while suppressing other transmission bands that would have been present without the metal layer. Here, we introduce a switchable mid-infrared ITF where the metal film can be "switched on and off", enabling the modulation of the filter response from single-band to multiband. The switching is enabled by a deeply subwavelength film of vanadium dioxide (VO2), which undergoes a reversible insulator-to-metal…
Tuning of Localized Surface Plasmons in Vanadium Dioxide Nanoparticles via Size and Insulator-Metal Transition
Brno University of Technology（布尔诺理工大学）；Central European Institute of Technology（中欧技术研究所）；Center for Nanophase Materials Sciences, Oak Ridge National Laboratory（橡树岭国家实验室纳米材料科学中心）
This paper proposes a reconfigurable planar metamaterial that can be switched between capacitive and inductive responses using local changes in the electrical conductivity of its constituent material. The proposed device is based on Babinet's principle and exploits the singular electromagnetic responses of metallic checkerboard structures, which are dependent on the local electrical conductivity. Utilizing the heating-induced metal-insulator transition of vanadium dioxide ($\mathrm{VO}_2$), the proposed metamaterial is designed to compensate for the effect of the substrate and is experimentall…
The insulator-to-metal transition (IMT) in vanadium dioxide (VO2) can enable a variety of optics applications, including switching and modulation, optical limiting, and tuning of optical resonators. Despite the widespread interest in optics, the optical properties of VO2 across its IMT are scattered throughout the literature, and are not available in some wavelength regions. We characterized the complex refractive index of VO2 thin films across the IMT for free-space wavelengths from 300 nm to 30 μm, using broadband spectroscopic ellipsometry, reflection spectroscopy, and the application of ef…
Sub-milliwatt threshold power and tunable-bias all-optical nonlinear activation function using vanadium dioxide for wavelength-division multiplexing photonic neural networks
We propose and analyze theoretically an approach for realizing a tunable optical phased-array antenna utilizing the properties of VO2 for electronic beam steering applications in the near-IR spectral range. The device is based on a 1D array of slot nano-antennas engraved in a thin Au film grown over VO2 layer. The tuning is obtained by inducing a temperature gradient over the device, which changes the refractive index of the VO2, and hence modifies the phase response of the elements comprising the array, by producing a thermal gradient within the underlying PCM layer. Using a 10-element array,…
Vanadium dioxide (VO2) transforms from purely monoclinic to purely tetragonal on being heated from 58 deg C to 72 deg C, the transformation being reversible but hysteretic. Electromagnetically, VO2 transforms from a dissipative dielectric to another dissipative dielectric if the free-space wavelength is less than 1100 nm, but from a dissipative dielectric to a plasmonic metal (or vice versa) if the free-space wavelength exceeds 1100 nm. Calculating the extinction, total scattering, absorption, radiation-pressure, back-scattering, and forward-scattering efficiencies of a VO2 sphere, we found cl…
We use apertureless scattering near-field optical microscopy (SNOM) to investigate the nanoscale optical response of vanadium dioxide (VO2) thin films through a temperature-induced insulator-to-metal transition (IMT). We compare images of the transition at both mid-infrared (MIR) and terahertz (THz) frequencies, using a custom-built broadband THz-SNOM compatible with both cryogenic and elevated temperatures. We observe that the character of spatial inhomogeneities in the VO2 film strongly depends on the probing frequency. In addition, we find that individual insulating (or metallic) domains ha…
Thermodynamics of the ultrafast phase transition of vanadium dioxide
IMDEA Nanoscience（IMDEA纳米科学研究所）；CNRS, Univ Rennes, Institut de Physique de Rennes（法国国家科学研究中心，雷恩大学，雷恩物理研究所）；The University of Tokyo（东京大学）；Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST（加泰罗尼亚纳米科学与技术研究所（ICN2），西班牙高等科学研究理事会和巴塞罗那综合理工学院）；Department of Physics and Astronomy, Aarhus University（奥胡斯大学物理与天文系）
We demonstrate spatial modification of the optical properties of thin-film metal oxides, zinc oxide and vanadium dioxide as representatives, using a commercial focused ion beam (FIB) system. Using a Ga+ FIB and thermal annealing, we demonstrated variable doping of a band semiconductor, zinc oxide (ZnO), achieving carrier concentrations from 10^18 cm-3 to 10^20 cm-3. Using the same FIB without subsequent thermal annealing, we defect-engineered a correlated semiconductor, vanadium dioxide (VO2), locally modifying its insulator-to-metal transition (IMT) temperature by range of ~25 degrees C. Such…
Vanadium Dioxide (VO2) is a strongly correlated material, which exhibits insulator to metal transition at ~68 C along with large resistivity and infrared optical reflectance modulation. In this work, we use atmospheric pressure thermal oxidation of Vanadium to synthesize VO2 films on glass and ITO coated glass substrates. With the optimized short oxidation durations of 2 min and 4 min, the synthesized VO2 film shows high optical reflectance switching in long-wavelength infrared on glass substrates and mid-wavelength infrared on ITO coated glass substrates, respectively. Peak reflectance switch…
Vanadium dioxide (VO2) as a phase-change material controls the transferred heat during phase transition process between metal and insulator states. At temperature above 68C, the rutile structure VO2 keeps the heat out and increases the IR radiation reflectivity, while at the lower temperature the monoclinic structure VO2 acts as the transparent material and increase the transmission radiation. In this paper, we first present the metal-insulator phase transition (MIT) of the VO2 in high and low temperatures. Then we simulate the meta-surface VO2 of metamaterial reflector by Ansys HFSS to show t…
We present the model of an ultrasensitive mid-infrared (mid-IR) photodetector operating in the mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) domains consisting of a hybrid heterostructure made of nanopatterned graphene (NPG) and vanadium dioxide (VO$_2$) which exhibits a large responsivity of $R\sim 10^4$ V/W, a detectivity exceeding $D^*\sim 10^{10}$ J, and a sensitivity in terms of noise-equivalent power $\mathrm{NEP}\sim 100$ fW/$\sqrt{\rm Hz}$ close to room temperature by taking advantage of the phase change of a thin VO$_2$ film. Our proposed photodetector can reach a…
