Properties Of Vanadium Dioxide Research Articles

Terahertz dynamic multichannel holograms generated by spin-multiplexing reflective metasurface.

In recent years, metasurfaces have attracted considerable interest for their unprecedented capabilities to manipulate intensity, phase, and polarization of an electromagnetic wave. Although metasurface-based wavefront modulation has achieved numerous successful results, implementation of multifunctional devices in a single metasurface still meet significant challenges. Here, a novel multilayer structure is designed using properties of vanadium dioxide (VO2). Propagation phase and geometric phase are introduced in this structure to achieve multichannel holographic imaging in terahertz band. When the temperature is above 68°C, VO2 becomes a metal and it plays a role in wavefront modulation for terahertz wave. The left-handed channel realizes a hologram letter L and the right-handed channel realizes a hologram letter R. When the temperature is below 68°C, VO2 changes to an insulator, and electromagnetic wave is controlled by gold structures embedded inside a VO2 film. In this case, hologram number 2 is realized in the left-handed channel and hologram number 6 appears in the right-handed channel. Our structure has advantages of low crosstalk, multiple channels, and large bandwidth. This novel design paves a new road for multichannel imaging and information encryption.

Infrared and Terahertz Spectra of Sn-Doped Vanadium Dioxide Films

This work reports the effect of tin (Sn) doping on the infrared (IR) and terahertz (THz) properties of vanadium dioxide (VO2) films. The films were grown by hydrothermal synthesis with a post-annealing process and then fully characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and temperature-controlled electrical resistivity as well as IR and THz spectroscopy techniques. Utilizing (NH4)2SnF6 as a Sn precursor allows the preparation of homogeneous Sn-doped VO2 films. Doping of VO2 films with Sn led to an increase in the thermal hysteresis width while conserving the high modulation depth in the mid-IR regime, which would be beneficial for the applications of VO2 films in IR memory devices. A further analysis shows that Sn doping of VO2 films significantly affects the temperature-dependent THz optical properties, in particular leading to the suppression of the temperature-driven THz transmission modulation. These results indicate Sn-doped VO2 films as a promising material for the development of switchable IR/THz dichroic components.

Electro-Thermal Simulation of Vertical VO2 Thermal-Electronic Circuit Elements

Advancement of classical silicon-based circuit technology is approaching maturity and saturation. The worldwide research is now focusing wide range of potential technologies for the “More than Moore” era. One of these technologies is thermal-electronic logic circuits based on the semiconductor-to-metal phase transition of vanadium dioxide, a possible future logic circuits to replace the conventional circuits. In thermal-electronic circuits, information flows in a combination of thermal and electronic signals. Design of these circuits will be possible once appropriate device models become available. Characteristics of vanadium dioxide are under research by preparing structures in laboratory and their validation by simulation models. Modeling and simulation of these devices is challenging due to several nonlinearities, discussed in this article. Introduction of custom finite volumes method simulator has however improved handling of special properties of vanadium dioxide. This paper presents modeling and electro-thermal simulation of vertically structured devices of different dimensions, 10 nm to 300 nm layer thicknesses and 200 nm to 30 μm radii. Results of this research will facilitate determination of sample sizes in the next phase of device modeling.

Thin Films of Nanocrystalline Vanadium Dioxide: Modification of the Properties, and Electrical Switching

Vanadium oxide films have been fabricated by the acetylacetonate and triethoxy vanadyl sol-gel methods on silicon substrates, as well as by magnetron sputtering on glass-ceramic substrates. Additional annealing in reducing atmosphere results in formation of vanadium dioxide or mixed phases with a VO2 predominance. The obtained films demonstrate the metal-insulator transition and electrical switching. In the films produced from triethoxy vanadyl, the peculiarities of electrical properties are related to the size effect, heterophase character of vanadium oxide films, and different types of charge carriers in the bulk of nanocrystallites and on their surfaces. Also, the effect of doping with hydrogen by means of plasma-immersion ion implantation on the properties of vanadium dioxide is explored. It is shown that the transition parameters in VO2 thin films depend on the hydrogen implantation dose. At doses exceeding a certain threshold value, the films are metallized, and the phase transition no longer occurs.

Fabrication of Phase Change Microstring Resonators via Top Down Lithographic Techniques: Incorporation of VO2/TiO2 Into Conventional Processes

The electronic, optical, and mechanical properties of vanadium dioxide (VO2) can be significantly altered by external stimuli such as heat, electric field, and so on, due to its metal-insulator transition (MIT). While the properties and potential applications of this material have been widely studied, minimal efforts were pursued to integrate VO2 into existing microfabrication processes. Here, in this paper, we present a process for fabricating VO2/TiO2-coated microstring resonators, where the stability of both films was monitored during the entire process. RIE, vapour HF, ablation, and ICP etching were used throughout the process and their effects on the VO2/TiO2 films, as well as the structural and masking layers was studied. Certain processes required the use of a metal hard mask rather than photo resist. VO2 shows excellent etch selectivity over the metal mask layer with RIE. Of all metals examined, Cr was found to be the most stable as a hard mask. Once fabricated, the mechanical and electrical characterizations of the microstring were carried out by measuring resonance frequency (fr) and electrical resistance which show over 6 % alteration in fr and two orders of magnitude change in resistance during the MIT, with a reversible transition and minimal hysteresis. This report provides a foundation for future processing of VO2 based MEMS/MOEMS devices.

Characteristics of RF Magnetron Sputtered VO2 Thin Films for Potential Applications of Solar Control Coatings

Properties of vanadium dioxide or vanadia (VO2) thin films prepared using radio frequency (RF) magnetron sputtering with a pure VO2 target were analysed. The properties consisted of crystal structure, surface topography, surface morphology as well as optical and thermochromic properties of VO2 thin films. The deposition was conducted in an argon atmosphere of flow rate of 30 sccm, substrate temperature of 500 °C and RF sputtering power of 100 W. The film, which was deposited with film thickness of 50 nm, exhibited a single orientation of (110) orientation. The film surface featured quite homogeneous and continuous surface topography, and spherical-like grains that represented grains in VO2(M) phase. The film had low surface roughness resulting in quite high optical transmittance and relatively low optical reflectance, at room temperature throughout visible and near-infrared regions. Meanwhile, the film also showed a phase transition at ∼65.0 °C with hysteresis width of 38 °C.

How optical excitation controls the structure and properties of vanadium dioxide

We combine ultrafast electron diffraction and time-resolved terahertz spectroscopy measurements to link structure and electronic transport properties during the photoinduced insulator-metal transitions in vanadium dioxide. We determine the structure of the metastable monoclinic metal phase, which exhibits antiferroelectric charge order arising from a thermally activated, orbital-selective phase transition in the electron system. The relative contribution of the photoinduced monoclinic and rutile metals to the time-dependent and pump-fluence-dependent multiphase character of the film is established, as is the respective impact of these two distinct phase transitions on the observed changes in terahertz conductivity. Our results represent an important example of how light can control the properties of strongly correlated materials and demonstrate that multimodal experiments are essential when seeking a detailed connection between ultrafast changes in optical-electronic properties and lattice structure.

Influence of Modifiers on the Morphology and Functional Properties of Vanadium Dioxide

Vanadium dioxide nanoparticles were obtained by the hydrothermal synthesis method in the presence of soluble Mo and W compounds as nucleating agents and of potassium and sodium chlorides as growth limiters. The influence of modifiers nature and synthesis conditions on the phase composition of the resulting product was studied.

Developments of Thermochromic VO2–Based Thin Films For Architectural Glazing

Investigation on properties of vanadium dioxide (VO2) thin films has received significant attention as it is a thermochromic material potentially for applications on architectural glazing in order to reduce energy consumption from usage of air-conditioning system. Most studies have focused on the hysteresis behavior of thermochromic VO2 thin films that occurs at a certain phase transition temperature. Although large area coating techniques have recently been developed, there are still many obstacles in trying to deploy energy-efficient windows. Hence, this work concisely reviews on VO2 thin films as thermochromic materials, and developments on preparation methodologies in order to enhance the thermochromic characteristics of VO2 thin films.

Influence of Iron Alloying on the Properties of Vanadium Dioxide

Results of investigations of the x-ray structural parameters of the crystal lattice and their temperature dependences in the vicinities of the metal-dielectric phase transition for V1–xFe x O2 solid solutions are reported together with results of comparison of x-ray and pycnometric densities of these materials. The defect concentration in the materials under study is estimated at room temperature.

Modification of the Properties of Vanadium Oxide Thin Films by Plasma-Immersion Ion Implantation

The paper describes the effect of doping with hydrogen and tungsten by means of plasma-immersion ion implantation (PIII) on the properties of vanadium dioxide and hydrated vanadium pentoxide films. It is shown that the parameters of the metal-insulator phase transition in VO2 thin films depend on the hydrogen implantation dose. Next, we explore the effect of PIII on composition, optical properties, and the internal electrochromic effect (IECE) in V2O5·nH2O films. The variations in the composition and structure caused by the hydrogen insertion, as well as those caused by the electrochromic effect, are studied by nuclear magnetic resonance, thermogravimetry, Raman spectroscopy, and X-ray structural analysis. It is shown that the ion implantation-induced hydrogenation can substantially enhance the manifestation and performance of the IECE in V2O5 xerogel films. Finally, the effect of PIII-assisted doping with W on the parameters of electrical switching in Au/V2O5·nH2O/Au sandwich structures is examined. It is shown that implanting small tungsten doses improves the switching parameters after forming. When implanting large doses, switching is observed without electroforming, and if electroforming is applied, the switching effect, on the contrary, disappears.

Modification of the properties of vanadium dioxide by plasma-immersion ion implantation

The effect of hydrogenation of thin films of vanadium dioxide by plasma-immersion ion implantation on their conductivity is characterized. It is demonstrated that the parameters of the metal–insulator phase transition observed in VO2 films depend on the irradiation dose. If the dose exceeds a certain threshold, film metallization occurs and the phase transition vanishes. The time of retention of hydrogen within films is considerably longer than that typical for other hydrogenation methods.

钨钒共溅掺杂二氧化钒薄膜的制备及其光学特性

钨钒共溅掺杂二氧化钒薄膜的制备及其光学特性

Electromagnetic wave modulation in hollow vanadium dioxide microcrystals

The optical properties of vanadium dioxide (VO2) single crystals with a hollow rectangular inner channel are numerically simulated. In such microstructures, electromagnetic waves are shown to propagate in the form of waveguide modes, and the semiconductor-metal phase transition in VO2 results in substantial modulation of the mode propagation constant. The propagation constants are calculated for TE, TM, and EH modes in the spectral range 0.8–1.3 μm.

00/03639 Stability of electrical properties of vanadium dioxide based ceramics

00/03639 Stability of electrical properties of vanadium dioxide based ceramics

Optical properties of vanadium dioxide thin film as a windows thermochromic coating

The optical properties of vanadium dioxide (VO 2 ) thin film have been studied for the potential application of intelligent windows. The results show that VO 2 film deposited on sapphire substrates exhibits good thermochromic effects, its IR transmittance changes 60% before and after phase transition, and has less thickness dependence than UV transmittance. Doping can significantly reduce transition temperature, such as to 30°C for 1.5% Mo doped VO 2 .

The influence of substrate temperature on the optical properties of ion-assisted reactively evaporated vanadium oxide thin films

The properties of vanadium dioxide (VO2) films bombarded with oxygen ions during deposition are examined as a function of substrate temperature. Electrical and optical properties of the as-deposited films are discussed. After annealing to the VO2 form, these films exhibit phase transition temperatures reduced from a nominal 67 °C, the lowest thus far in this series being 38 °C. Rutherford backscattering analysis indicates low-level tungsten contamination of the films, presumably from the ion gun filaments. The contaminant has a role in properties modification but does not provide a complete explanation for our observations.