Vanadium Dioxide Layer Research Articles

Design and theoretical analysis of near-infrared multiband metamaterial absorber with concentric sub-resonators for solar applications

Metamaterial absorbers with multiple frequency bands can be designed by stacking sub-resonators vertically or arranging them co-planarly. However, to increase the number of absorption peaks, we often need more sub-resonators. Therefore, a study explores dynamic infrared multiband metamaterial absorbers to enhance electromagnetic wave absorption and addresses tunability challenges by utilizing a periodic sub-wavelength structure-based unit cell. The novel design comprises a concentric triangular strip within a central hollow of a square patch, with four hollow cylindrical spaces at the patch corners, each containing four small square pillars. The design comprises a metal–dielectric–metal architecture, with silver as the top patch and the ground metal layer separated by a thin magnesium fluoride dielectric layer. A temperature-controlled material vanadium dioxide layer is introduced below the upper metal layer to enhance the absorbance. Moreover, extensive parametric investigations have been conducted involving the manipulation of shape while keeping other dimensions constant. The goal is achieving perfect multiple absorptions within the 90–300 THz frequency range, ensuring impedance match and exhibiting plasmonic resonance characteristics. The study also investigates unit cell behavior regarding polarization and incident angle variations. Simulations are conducted using CST Microwave Studio Suite® with finite integration technology and validated with COMSOL Multiphysics® using the finite element method in the frequency domain. The simulated results reveal multiple absorption peaks in the terahertz range, averaging 98.32% with a maximum absorption of up to 99.99% and exhibiting high absorption coefficients at discrete resonance frequencies, suggesting promising applications in terahertz technology-related fields.

Multi-wavelength and broadband plasmonic switching with V-shaped plasmonic nanostructures on a VO2 coated plasmonic substrate

In this paper, periodic arrays of identical V-shaped gold nanostructures and variable V-shaped gold nanostructures are designed on top of a gold-coated silicon dioxide (SiO2) substrate with a thin spacer layer of vanadium dioxide (VO2) to realize multi-wavelength and broadband plasmonic switches, respectively. The periodic array of identical V-shaped nanostructures (IVNSs) with small inter-particle separation leads to coupled interactions of the elementary plasmons of a V-shaped nanostructure (VNS), resulting in a hybridized plasmon response with two longitudinal plasmonic modes in the reflectance spectra of the proposed switches when the incident light is polarized in the x-direction. The x-direction is oriented along the axis that joins the V-junctions of all VNSs in one unit cell of the periodic array. On exposure to temperature, electric field, or optical stimulus, the VO2 layer transforms from its monoclinic semiconducting state to its rutile metallic state, leading to an overall change in the reflectance spectra obtained from the proposed nanostructures and resulting in an efficient multi-wavelength switching action. Finite difference time domain modelling is employed to demonstrate that an extinction ratio (ER) >12 dB at two wavelengths can be achieved by employing the proposed switches based on periodic arrays of IVNSs. Further, plasmonic switches based on variable V-shaped nanostructures—i.e. multiple VNSs with variable arm lengths in one unit cell of a periodic array—are proposed for broadband switching. In the broadband operation mode, we report an ER >5 dB over an operational wavelength range >1400 nm in the near-IR spectral range spanning over all optical communication bands, i.e. the O, E, S, C, L and U bands. Further, it is also demonstrated that the wavelength of operation for these switches can be tuned by varying the geometrical parameters of the proposed switches. These switches have the potential to be employed in communication networks where ultrasmall and ultrafast switches with multi-wavelength operation or switching over a wide operational bandwidth are inevitably required.

Reconfigurable image processing metasurfaces with phase-change materials.

Optical metasurfaces have enabled analog computing and image processing within sub-wavelength footprints, and with reduced power consumption and faster speeds. While various image processing metasurfaces have been demonstrated, most of the considered devices are static and lack reconfigurability. Yet, the ability to dynamically reconfigure processing operations is key for metasurfaces to be used within practical computing systems. Here, we demonstrate a passive edge-detection metasurface operating in the near-infrared regime whose response can be drastically modified by temperature variations smaller than 10 °C around a CMOS-compatible temperature of 65 °C. Such reconfigurability is achieved by leveraging the insulator-to-metal phase transition of a thin layer of vanadium dioxide, which strongly alters the metasurface nonlocal response. Importantly, this reconfigurability is accompanied by performance metrics-such as numerical aperture, efficiency, isotropy, and polarization-independence - close to optimal, and it is combined with a simple geometry compatible with large-scale manufacturing. Our work paves the way to a new generation of ultra-compact, tunableand passive devices for all-optical computation, with potential applications in augmented reality, remote sensing and bio-medical imaging.

Multifunctional 2-bit coded reconfigurable metasurface based on graphene-vanadium dioxide

In this paper, a graphene-vanadium dioxide-based reconfigurable metasurface unit structure is proposed. Using the change at a graphene Fermi energy level on the surface of the unit structure to satisfy the 2-bit coding condition, four reflection units with a phase difference of 90∘ can be discovered. The modulating impact of the multi-beam reflection wave with 1-bit coding is then confirmed. Then we study the control of a single-beam reflected wave by metasurfaces combined with a convolution theorem in a 2-bit coding mode. Finally, when vanadium dioxide is in an insulating condition, the structure can also be transformed into a terahertz absorber. It is possible to switch between a reflection beam controller and a terahertz multifrequency absorber simply by changing the temperature of the vanadium dioxide layer without retooling a new metasurface. Moreover, compared with the 1-bit coded metasurface, it increases the ability of single-beam regulation, which makes the device more powerful for beam regulation.

Tunable and switchable multifunctional terahertz meta-mirror based on graphene and vanadium dioxide.

We design a multifunctional THz polarization modulation meta-mirror integrated with polarization conversion and dichroism functions switched by temperature and voltage. The meta-mirror is composed of two-layered graphene metasurfaces and a layer of vanadium dioxide (VO2) on a gold film substrate. Linear-to-linear polarization conversion and linear dichroism (LD) can be switched by temperature control in the VO2 film and Fermi level adjustments in the graphene metasurfaces, where the polarization conversion ratio (PCR) is higher than 0.9 in the range of 2.89 THz to 4.02 THz, LD value reached a maximum of 0.6 at 3.84 THz, and linear-to-circular polarization conversion and circular dichroism (CD) can also be tuned with ellipticity higher than 0.9 in the range of 2.32 THz to 2.69 THz and CD value as high as 0.71 at 2.45 THz. The proposed meta-mirror is the first THz metamaterial device integrating four switchable functions, including linear-to-linear polarization conversion, linear-to-circular polarization conversion, linear dichroism and circular dichroism. The meta-mirror is a promising design for compact system integration in THz imaging, sensing and biological detection applications.

Multifunctional terahertz device with active switching between bimodal perfect absorption and plasmon-induced transparency

In this paper, we propose a terahertz (THz) micronano device that can actively switch between bimodal absorption and plasmon-induced transparency (PIT). The device mainly consists of a continuous top layer of graphene, an intermediate layer of silica and a bottom layer of vanadium dioxide, and has a simple structure, easy tuning and wide angle absorption. Through impedance matching and electromagnetic field distribution, we explain the generation of perfect absorption with double peaks. The simulation and multiple reflection interference theory (MRIT) show that the device achieves perfect absorption at 3.02 THz and 3.68 THz, and is highly sensitive to environmental refractive index, with a sensitivity of 1.1 THz/RIU. In addition, when the PIT effect is realized through the phase change characteristic of VO2, the device not only has the function of three-frequency asynchronous optical switch, but also has a strong slow light effect, and the maximum group delay (τg) is 35.4 ps. Thus, our design allows simultaneous switching, modulation, sensing, and slow light functions in the optical path and will greatly facilitate the development of THz multifunctional devices.

A simple structured and homo-frequency point mode switchable THz full-space metasurface based on temperature-controlled vanadium dioxide

Terahertz (THz) full-space metasurfaces have attracted great attention in the field of modern communication systems due to their inherent advantages in electromagnetic (EM) wave manipulation. However, nearly all the reported full-space metasurfaces are realized by multilayer dielectric cascade structures. Furthermore, for mode switchable metasurfaces, reflection and transmission modes are always switched at different frequency points, which limits their application prospects. In this paper, we propose a full-space THz metasurface that can switch between reflection and transmission modes at the same frequency point only by controlling a single substrate layer of vanadium dioxide. The reflection and transmission properties can be independently controlled by rotating the optimized meta-atoms on the metasurface independently. To demonstrate its application potential for multifunctional devices, full-space focusing vortex beam generator and near-field imaging are practiced. A mode switchable focusing vortex beam generator using right circularly polarized (RCP) light at 1.312 THz is designed. The mode purity of the vortex beam under both the transmission and reflection directions is above 85 %. Then a full-space near-field imaging of letters “UPC” at 200 μm from the reference plane is achieved both in the reflection and transmission direction. The transmission and reflection modes can be switched simply by regulating the temperature of the vanadium dioxide substrate through a thermistor. Our suggested design concept of homo-frequency points and simple structure is more conducive to future practical engineering applications of metasurface and provides a worthwhile direction for future research of full-space functional devices.

Terahertz metamaterials for broadband, high modulation depth modulator, and tunable dual-band absorber based on metal-vanadium dioxide hybrid structure

Terahertz metamaterials for broadband, high modulation depth modulating, and tunable dual-band absorbing are designed based on the similar composite structure of metal and vanadium dioxide film arrays. By using external excitation to induce the insulator-metal phase transition of the vanadium dioxide layer, the transmission characteristics of the metamaterial can be manipulated. High modulation depths of more than 80% are achieved in the range of 0.2–0.8 THz, and the bandwidth width with modulation depths exceeding 60% is up to 140%. By increasing the dielectric thickness and adding a metal ground, the initial broadband modulator can be switched to a dual-band absorber when the vanadium dioxide is in the metal phase. Furthermore, the modulation effect and the absorption performance exhibit insensitive characteristics to the polarization angle of incident waves. This work provides potential applications in broadband modulation of terahertz communication as well as dual-band absorption for terahertz detection.

Analogy of polarization-independent, multi-band and tunable electromagnetically induced transparency with high sensitivity based on simple circular ring resonators and vanadium dioxide film

An analogy of polarization-independent, multi-band and tunable electromagnetically induced transparency (EIT) effect is proposed based on simple combination of circular ring resonators and vanadium dioxide film. The EIT-like effect is generated by bright-bright coupling resulting from adjacent ring resonators. High sensitivity up to 1.60 THz/RIU to the environmental refractive index is achieved utilizing the transparency peak. Accompanying with the EIT-like effect, the multi-band slow light phenomenon is obtained around the transparency windows. In addition, by inducing the insulator-metallic transition of the vanadium dioxide layer, the EIT-like curves can be actively manipulated while the multiple modulation is realized without refabricating the structure. Particularly, due to structural symmetry, the EIT-like windows keep unchanged and maintain noticeable with various polarization angles. The proposed structure has potential applications such as terahertz sensors, slow-light devices and modulators.

Single-frequency into dual-frequency absorption switch based on a one-dimensional photonic crystal containing graphene and vanadium dioxide layers

A terahertz absorber based on a one-dimensional photonic crystal (1DPC) containing VO2 and graphene sheet that connects single-frequency into dual-frequency absorption by temperature control is proposed in this paper. The structure consists of a graphene sheet on the Si layer, a Bragg reflector, and a VO2 layer at the end. At 300 K, the VO2 layer is in its insulator phase, and the structure behaves as a single-frequency absorber with 95% absorptivity at 0.472 THz (f1 mode). When temperature varies to 350 K, the VO2 transfer to the metallic phase and the proposed structure can be utilized as a dual-frequency absorber with 98% and 99% absorptivity at 0.472 THz and 0.523 THz (f2 mode), respectively. The physical reason for the absorption modes is explained by the electric field distribution and impedance-matching technique. The frequency position of the absorption modes, and their absorptivity can be tuned by adjusting the Fermi energy of graphene and the period numbers of 1DPC. Also, the first mode absorption shows high absorptivity over a wide incident angle range for TE and TM polarization at both temperatures; in contrast, the second mode absorption at 350 K vanishes over 25˚ of incidence angle. The proposed optical absorber would have potential applications in THz biosensors, filters, and emitters.

Hybrid Electrothermal Model for Insulator-to- Metal Transition in VO2 Thin Films

Comprehensive model for the insulator to metal phase transition in vanadium dioxide thin film in the presence of external electrical stimulus is proposed. This model divides the film layer into several segments and solves the Joule heating equations due to current flow and heat exchange with the environment and Poole–Frankel equation to obtain carrier concentration in response to the applied voltage, and transition is checked for each cell separately. The model follows the experimental results and exhibits both switching and hysteresis effect in planar structures and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}$ </tex-math></inline-formula> -shaped current–voltage characteristics in sandwich metal–insulator–metal structure based on the vanadium dioxide thin film. This model shows that by reducing the vanadium dioxide layer thickness, the electric field-assisted transition plays the dominant role in the transition, and therefore, it is a promising tool for the design and analysis of vanadium dioxide structures with various electrode distances.

Development of a tunable terahertz absorber based on temperature control

AbstractMetamaterial structure‐based terahertz absorbers all are passive, once the preparation is complete, their absorption properties are also determined unable to adapt to the increasingly complex electromagnetic environment. In this paper, a kind of phase change film‐based tunable terahertz metamaterial absorber is proposed. And on the basis of current three‐layer type terahertz absorber on present metamaterial structure, a layer of vanadium dioxide (VO2) phase change film is added to change the conductivity of VO2 by controlling ambient temperature, so as to trigger the insulator metal transition characteristics of VO2 film, which can control the absorption rate of terahertz metamaterial absorber. Theoretically, design scheme in this paper has 80% modulation depth to the amplitude of absorption. That is, tunable terahertz electromagnetic absorber has potential application value in electromagnetic stealth in terahertz band, radiation detectors, and broadband communication fields.

Microwave Tunable Devices on the YIG-VO2 structures

The theory describing a tunability of the spin-wave spectrum for the ferrite/vanadium dioxide layered structures through changing the VO2 conductivity is suggested. An influence of the various parameters on the spin-wave wavenumber variations and damping decrement is studied. We show that an effective wavenumber variation with minimal losses is achieved by matching the thicknesses of the ferrite and vanadium dioxide films, as well as the value of external magnetic field. We show also that owing to the electrodynamic interaction, a quality of contact between the ferrite and vanadium dioxide layers is not critical.

Polarization-Independent Terahertz Tunable Analog of Electromagnetically Induced Transparency

The analogs of electromagnetically induced transparency (EIT) based on the concept of metamaterials (MMs) bring the primitive quantum phenomena into the scope of classical optics. However, most of the previous designs are anisotropic. Here, in this letter, a tunable isotropic classical analog of EIT is studied based on the wide-angle MM with a layer of vanadium dioxide underneath it. The tunable conductivity of vanadium dioxide is the key point to realize the dynamic modulation of EIT. The numerical calculation tells that the transmission peak of EIT can be tuned from 66% to 12% when the conductivity of vanadium dioxide is changed from 10 to $2000\;\Omega ^{-1}$ cm−1. Furthermore, such design possesses a nearly insensitive characteristic of transmission on polarization and incident angle. Although the simple planar structure presented here is a specific design to manipulate EIT-like phenomenon in terahertz MMs, it can be easily scaled to other electromagnetic spectra. This letter could provide one possible way for the plasmonic filter and sensing application.

Tunable polaritonic metasurface absorbers in mid-IR based on hexagonal boron nitride and vanadium dioxide layers

Here, a metasurface absorber with switchable spectral response is proposed and discussed. The device is constructed by combining a phase change material (vanadium dioxide, VO2) and a naturally hyperbolic materials (hexagonal boron nitride, hBN), utilizing surface plasmon polaritons (SPPs) and surface phonon polaritons (SPhPs), respectively, at different thermal conditions in the same system. Specifically, we take advantage of the excitation of SPhP in hBN below the VO2 critical temperature (T < Tc) and SPP from VO2 layers at higher temperatures (T > Tc), to switch between narrow-band near-perfect absorption at ~7.2 μm to broadband absorption at 8–12 μm. It is shown that SPPs and SPhPs can be excited, respectively, by controlling the temperature, offering new opportunities in designing tunable artificial materials and devices for promising nanophotonics applications.

Mass ablated controlled laser induced V2O5 plasma parameters for controllable VO2 films growth

The effect of the laser fluence on V2O5 plasma dynamics, composition, and ionization state was studied. By combining three plasma diagnostic techniques, fast imaging, optical emission spectroscopy, and Langmuir probe, two ablation regimes have been identified. These ablation regimes depend on the evolution of the amount of the ablated mass that was measured by the method of mass loss. The transition between the two regimes at 1.3 J cm−2. For fluences lower than this threshold value, the expansion velocity of the plasma elements, the plasma dimensions, and the ionic current increase rapidly, unlike the fluences higher than the threshold fluence. Reverse behavior was observed for the ablated mass. This effect of the ablated mass would have a significant impact on the control of the properties of vanadium dioxide layers deposited by pulsed laser deposition in a reactive atmosphere of oxygen.

Photoinduced surface plasmon switching at VO2/Au interface.

Angle-resolved reflection, light scattering and ultrafast pump-probe spectroscopy combined with a surface plasmon-polariton (SPP) resonance technique in attenuated total reflection geometry was used to investigate the light-induced plasmonic switching in a photorefractive VO2/Au hybrid structure. Measurements of SPP scattering and reflection shows that the optically-induced formation of metallic state in a vanadium dioxide layer deposited on a gold film significantly alters the electromagnetic field enhancement and SPP propagation length at the VO2/Au interface. The ultrafast optical manipulation of SPP resonance is shown on a picosecond timescale. Obtained results demonstrate high potential of photorefractive vanadium oxides as efficient plasmonic modulating materials for ultrafast optoelectronic devices.

Extraordinary pseudocapacitive energy storage triggered by phase transformation in hierarchical vanadium oxides

Pseudocapacitance holds great promise for improving energy densities of electrochemical supercapacitors, but state-of-the-art pseudocapacitive materials show capacitances far below their theoretical values and deliver much lower levels of electrical power than carbon-based materials due to poor cation accessibility and/or long-range electron transferability. Here we show that in situ corundum-to-rutile phase transformation in electron-correlated vanadium sesquioxide can yield nonstoichiometric rutile vanadium dioxide layers that are composed of highly sodium ion accessible oxygen-deficiency quasi-hexagonal tunnels sandwiched between conductive rutile slabs. This unique structure serves to boost redox and intercalation kinetics for extraordinary pseudocapacitive energy storage in hierarchical isomeric vanadium oxides, leading to a high specific capacitance of ~1856 F g–1 (almost sixfold that of the pristine vanadium sesquioxide and dioxide) and a bipolar charge/discharge capability at ultrafast rates in aqueous electrolyte. Symmetric wide voltage window pseudocapacitors of vanadium oxides deliver a power density of ~280 W cm–3 together with an exceptionally high volumetric energy density of ~110 mWh cm–3 as well as long-term cycling stability.

Tunable optical switching in the near-infrared spectral regime by employing plasmonic nanoantennas containing phase change materials

We propose the design of switchable plasmonic nanoantennas (SPNs) that can be employed for optical switching in the near-infrared regime. The proposed SPNs consist of nanoantenna structures made up of a plasmonic metal (gold) such that these nanoantennas are filled with a switchable material (vanadium dioxide). We compare the results of these SPNs with inverted SPN structures that consist of gold nanoantenna structures surrounded by a layer of vanadium dioxide (VO2) on their outer surface. These nanoantennas demonstrate switching of electric-field intensity enhancement (EFIE) between two states (On and Off states), which can be induced thermally, optically or electrically. The On and Off states of the nanoantennas correspond to the metallic and semiconductor states, respectively of the VO2 film inside or around the nanoantennas, as the VO2 film exhibits phase transition from its semiconductor state to the metallic state upon application of thermal, optical, or electrical energy. We employ finite-difference time-domain (FDTD) simulations to demonstrate switching in the EFIE for four different SPN geometries - nanorod-dipole, bowtie, planar trapezoidal toothed log-periodic, and rod-disk - and compare their near-field distributions for the On and Off states of the SPNs. We also demonstrate that the resonance wavelength of the EFIE spectra gets substantially modified when these SPNs switch between the two states.

An Optically-Triggered Switchable Mid-Infrared Perfect Absorber Based on Phase-Change Material of Vanadium Dioxide

Switchable nanoscale devices can be implemented in heterostructures that integrate plasmonic nanostructures with functional active materials and hence hold great potential for nanoscale-integrated circuits. The phase-change material of vanadium dioxide (VO2) has reversibly switchable optical/electrical properties and huge contrast in its refractive index in the infrared spectral range between insulator and metallic states. In this work, we numerically demonstrate all-optical manipulation of switchable absorption effect using the heterostructure incorporating the plasmonic resonance of Au nanoantennas with vanadium dioxide. Compared with the planar control device (without Au nanoantennas), the proposed design exhibits a pronounced resonant field enhancement as well as polarization-insensitive and omnidirectional absorption response. Meanwhile, the proposed device shows a large switching contrast (from ~ 99.9 to ~ 10% in absorption efficiency) at the mid-infrared wavelength of 3609 nm. Interestingly, the resonance of the proposed device can be continuously tuned by varying the side length of the antennas or governing the metallization level of vanadium dioxide layer. The photothermal mechanism is further investigated by numerical model calculations, indicating that the resonant, antenna-mediated local heating occurs on a sub-nanosecond time scale of 0.26 ns under a quite low incident intensity of 1.9 × 106 W/m2, which is about 12.5 times reduced with respect to that of control device. Therefore, the hybrid strategy of plasmonic antennas and vanadium dioxide provides a conceptual framework of switchable metamaterials for actively steering in ultrafast, energy-efficient electronic and photonic devices.