VO2 Temperature Research Articles

Multifunctional terahertz absorber based on the Dirac semimetal and vanadium dioxide.

In this paper, a multifunctional terahertz (THz) absorber based on Dirac semimetal and vanadium dioxide (V O 2) is proposed. By modulating the temperature of V O 2, the absorber can be switched between the narrow band and wide band. When V O 2 is in the metallic state, the absorber has a broadband absorption effect with a bandwidth of approximately 4THz. It has the advantages of insensitivity to polarization and wide-angle absorption. When V O 2 is in the insulating state, the absorber has two absorption peaks with absorptivity exceeding 90% and sensitivities of 297.7 and 402GHz/RIU, and thus can be used as a highly sensitive sensor for cell detection. When the Fermi level of the Dirac semimetal is changed, the absorption characteristics can be modulated. The absorber has broad application prospects in multifunctional modulated devices.

Effect of Sn on formation and transformation of VO2 phase

The role of stannum was investigated in formation and transformation of vanadium-dioxide phase in a deep perspective through characterization methods including Raman spectra, XRD, OM, SEM, UV–vis and electrochemical workstation. The result showed supersaturated stannum atoms could exist in SnxV2-xO5 as amorphous solid solution through non-equilibrium sputtering method, by which the unitary phase Sn-doped VO2 could be obtained under either thermal de-oxidation or thermal de-composition mechanism. Furthermore, cooperating stannum atoms with oxygen vacancies could regulate the formation of vanadium dioxide M1 or M2 phase, in turn engineer the phase transformation (M-R) temperature of VO2.

Switchable Terahertz Absorber from Single Broadband to Dual Broadband Based on Graphene and Vanadium Dioxide.

A multifunctional switchable terahertz (THz) absorber based on graphene and vanadium dioxide (VO2) is presented. The properties of the absorber are studied theoretically by the finite-difference time-domain (FDTD) method. The results illustrate that the structure switches between the single-broadband or double-broadband absorption depending on the temperature of VO2. Moreover, the amplitude of the absorptivity can be adjusted by changing the Fermi energy level (EF) of graphene or the conductivity of VO2 separately. Via impedance matching theory, the physical mechanism of the absorber is researched. Furthermore, the effects of incidence angle on absorption have also been studied. It is found that the absorber is insensitive to the polarization of electromagnetic waves.

Tunable multiband absorber based on metamaterial in the terahertz region

A multiband tunable metamaterial terahertz absorber based on VO2 material is introduced and studied. The absorber consists of gold planes and periodic metallic materials. The first layer is gold plane, the second layer is polyimide, the third layer is silicon film, and the fourth layer is super surface. From the simulation results, we can see that the phase transition occurs when the temperature of VO2 is greater than or equal to 68°C. After the phase transition, there are three absorption peaks, and the absorption rates are more than 99% at 2.53, 5.7, and 8.67 THz, realizing perfect absorption. When the temperature of VO2 is less than 68°C, the maximum absorption rate is 30.4%, which fails to meet the absorption requirements. By increasing the thickness of polyimide, the absorption spectrum moves slightly to the low frequency band to achieve redshift. Compared with most of the proposed multiband absorbers, the metamaterial absorber with adjustable absorption spectrum has better application prospects. VO2 is a phase change material with insulator metal phase transition characteristics and reversible process. By using the phase transition characteristics of VO2, the absorber has a switching function and is conducive to the flexible regulation of the absorption spectrum.

Dual-Tunable Polarization Insensitive Electromagnetically Induced Transparency in Metamaterials

A multilayer structure of a square ring of graphene with nesting vanadium dioxide (VO2) was investigated in this study. This structure exhibits electromagnetically induced transparency (EIT), which stems from a bright mode coupling with a dark mode. The permittivity values of graphene and VO2 can be modulated via chemical potential and temperature, respectively. The EIT effect can be tuned based on the chemical potential of graphene and temperature of VO2, resulting in a dual-tunable EIT effect. Simulation results confirmed that this dual-tunable EIT phenomenon is insensitive to polarization. These results may have potential applications in terahertz devices, such as slow light devices, switching devices, and sensors.

Magneto-optical and thermo-optical modulations of Goos-Hänchen effect in one-dimensional photonic crystal with graphene-VO2

We have theoretically studied the magneto-optical and thermo-optical modulations of Goos-Hänchen (GH) effect in a one-dimensional photonic crystal with graphene-vanadium dioxide (VO2) periodic structure. Due to the characteristics of graphene and VO2 in the terahertz region, this structure can be used for magnetic field and temperature modulation. Magneto-Optical effect of graphene in the terahertz region and the first-order metal–insulator transition (MIT) of VO2 near 68 degreesC will have a significant effect on the GH shift modulation. We obtain their relationship between the amplified GH shift with the VO2 temperature under the magnetic field environment, and the relationship between the magnetic field and VO2 is in the insulation (298 K) and the metallic state (358 K), respectively. In the case of a constant magnetic field, the increase of temperature will decrease the GH shift before and after amplification, and the increase of magnetic field will significantly enhance the GH shift, including VO2 in a fully insulated state and a metallic state, respectively. This provides a new idea and method for the design of terahertz equipment which modulates by temperature and magnetic.

Thermally Controllable Infrared Absorption in Cylindrical Groove Array Covered by Phase Change Material

A perfect infrared spectrum absorber in a cylindrical groove array perforated in a metallic layer and followed by vanadium dioxide (VO2), a phase-change material, is introduced and analytically investigated. The phase-change material can change from insulator to metallic phase if proper stimuli, such as heat, voltage, and current, are applied, herein the phase change initiated by heating beyond the phase-transition temperature of VO2. The large refractive index variations between two phases enable the manipulation of optical properties. Simulation results reveal that in the metallic phase, the absorption is suppressed to one third, while VO2 works as a transparent medium for impinging light, and perfect absorption is observed in the insulation phase. The process is reversible in a picosecond time scale. Given the structure symmetry, the absorption is irreverent to impinging light polarization. The thermally controlled infrared absorber may have applications in various optical systems, like imaging and sensing, due to its simple and easy fabrication process.

Study on Transport Property of VO2 thin Film Observed by Temperature and Magnetic Field Dependence of Hall Effect and Temperature Dependence of Seebeck Effect

Here, we investigated the temperature and magnetic-field-dependent Hall effect and temperature-dependent Seebeck effect in VO₂ thin films by using physical property measurement systems. It was observed from the ordinary Hall effect measurement from room temperature to 370K that the Hall voltage decreased with increasing external magnetic field and dominant carriers changed near the critical temperature where an insulator-to-metal transition in VO₂ was triggered. The decrease of the Hall voltage implies the weakening of the strong electron correlation with increasing applied magnetic field. In the case of the Seebeck coefficient in VO₂ thin films, its negative slope variation was obtained with respect to the temperature gradient between two ends of the VO₂ film at room temperature. The Seebeck coefficient could be evaluated as -250 and -28㎶/K at 300 and 360K, respectively. Near the critical temperature of VO₂, the rate of change in the Seebeck coefficient with respect to the temperature gradient showed a gradual decrease in its magnitude and then changed its sign with increasing temperature gradient. This peculiar variation of the rate of change in the Seebeck coefficient in the vicinity of the critical temperature seems to stem from the percolated motion of the structural phase transition in VO₂.

Phase transition characteristics of vanadium oxide films under the CO2 laser irradiation

Vanadium oxide is a type of thermochromic material. At a certain temperature it undergoes a phase transition, The phase transition temperature of VO2 is about 68°C.Using the magnetron sputtering method, vanadium oxide thin films were prepared on glass substrates. Heat treatment was carried out. The film was analysed using X-ray diffraction (XRD) spectrum. The result shows that the main constituents of the film are VO2 and V2O3. A beam of CO2 laser was directed to the film. A laser power meter was used to measure the specular reflection power from the film. The test results showed that the temperature of the film and its base rose fast when the laser irradiated on it and a semiconductor-metal phase transition occurred in the film. As a result, the film's reflectivity grew high. The specular reflectivity of 10.6 μm laser from the film rose 76.4% after the phase transition.