As a strongly correlated metal oxide, VO2 inspires several highly technological applications. The challenging reliable wafer-scale synthesis of high quality polycrystalline VO2 coatings is demonstrated on 4” Si taking advantage of the oxidative sintering of chemically vapor deposited VO2 films. This approach results in films with a semiconductor-metal transition (SMT) quality approaching that of the epitaxial counterpart. SMT occurs with an abrupt electrical resistivity change exceeding three orders of magnitude with a narrow hysteresis width. Spatially resolved infrared and Raman analyses evidence the self-assembly of VO2 disordered metamaterial, compresing monoclinic (M1 and M2) and rutile (R)domains, at the transition temperature region. The M2 mediation of the M1-R transition is spatially confined and related to the localized strain-stabilization of the M2 phase. The presence of the M2 phase is supposed to play a role as a minor semiconducting phase far above the SMT temperature. In terms of application, we show that the VO2 disordered self-assembly of M and R phases is highly stable and can be thermally triggered with high precision using short heating or cooling pulses with adjusted strengths. Such a control enables an accurate and tunable thermal control of the electrical switching.

https://cyberleninka.org/article/n/702062.pdf

Electrical Switching in Semiconductor-Metal Self-Assembled VO2 Disordered Metamaterial Coatings.

Although di-vanadium pentoxide (V2O5) has been a candidate of extensive research for over half a century, its intrinsic thermochromism has not been reported so far Films of V2O5 grown on silicon, glass, and metal substrates by metal organic chemical vapor deposition in this study exhibit a thermally induced perceptible color change from bright yellow to deep orange Temperature-dependent UV–vis spectroscopy and X-ray diffraction allow the correlation between the reversible continuous red shift of the absorption and the anisotropic thermal expansion along the (001) direction, that is, perpendicular to the sheets constituting the layered structure Furthermore, the possibility of tuning the thermochromic behavior was demonstrated via a chemical doping with chromium

https://hal.archives-ouvertes.fr/hal-01651488/document

Visible Thermochromism in Vanadium Pentoxide Coatings.

Vanadium oxide thin films were grown on both quartz and Si(111) substrates, utilizing a pulsed RF magnetron sputtering technique at room temperature with the RF powers at 100 W to 700 W. The corresponding thicknesses of the films were increased from 27.5 nm to 243 nm and 21 nm to 211 nm as the RF power was increased from 100 W to 700 W for the quartz and silicon substrates, respectively. X-ray diffraction and field emission scanning electron microscopy were carried out to investigate the phase and surface morphology of the deposited films. The electronic structure and the vanadium oxidation states of the deposited films were investigated thoroughly by X-ray photoelectron spectroscopy. The as-grown films show only stoichiometric vanadium oxide, where vanadium is in V5+ and V4+ states. The phase transitions of the vanadium oxide films were investigated by the differential scanning calorimetric technique. The reversible i.e. smart transition was observed in the region from 337 °C to 343 °C. The average hemispherical infrared emittance of the deposited vanadium oxide films was evaluated by an emissometer in the wavelength range of 3 μm to 30 μm. The sheet resistance of the deposited films was measured by a two-probe method and the data were in the range of 106 to 105 Ω per square. The optical properties of the films, such as solar transmittance, solar reflectance and solar absorptance, as well as optical constants e.g. optical band gap, were also evaluated. Finally, mechanical properties such as the hardness and the Young’s modulus at the microstructural length scale were evaluated by employing a nanoindentation technique with a continuous stiffness mode.

Study of the structural, thermal, optical, electrical and nanomechanical properties of sputtered vanadium oxide smart thin films

Preparation, infrared emissivity and thermochromic properties of Co doped ZnO by solid state reaction

Highly axis-oriented V2O5 thin films were fabricated by metal–organic decomposition (MOD) on SiO2/Si substrates. V2O5 thin films were reduced to VOx thin films by heat treatment with a temperature of 530–580 °C, pressure of 1.2–3 Pa in O2 and heating time of 2–5 h. The VOx thin films exhibited an abrupt transition, with a resistivity change of up to 3 orders of magnitude at a transition temperature of about 55 °C. The hysteresis loop width in the transition was about 3 °C. The grain size of the VOx thin films with an abrupt transition was 200–300 nm. Furthermore, these films had a temperature coefficient of resistivity (TCR) of up to 2.2%/K at 300 K.

https://iopscience.iop.org/article/10.1143/JJAP.50.025803/pdf

Characteristics of Vanadium Oxide Thin Films Prepared by Metal?Organic Decomposition for Bolometer Detectors

Thermochromic vanadium dioxide (VO2) exhibits a semi-conducting to metallic phase transition at about 68°C, involving strong variations in electrical and optical properties A simple method was proposed to prepare VO2 thin films from easily gained V2O5 thin films The detailed thermodynamic calculation was done and the results show that V2O5 will decompose to VO2 when the post annealing temperature reaches 550°C at the atmospheric pressure of less than 006Pa The initial V2O5 films were prepared by sol-gel method on fused-quartz substrates Different post annealing conditions were studied The derived VO2 thin film samples were characterized using X-ray diffraction and X-ray photoelectron spectroscopy The electrical resistance and infrared emissivity of VO2 thin films under different temperatures were measured The results show that the VO2 thin film derived from the V2O5 thin film annealed at 550°C for 10 hours is pure dioxide of vanadium without other valences It was observed that the resistance of VO2 thin film with thickness about 600nm can change by 4 orders of magnitude and the 75-14μm emissivity can change by 06 during the phase transition

Thermochromic VO2 Thin Film Prepared by Post Annealing Treatment of V2O5 Thin Film

Three-dimensional carbon fiber reinforced mullite composites (3D-Cf/mullite) were fabricated by sol-gel method with diphasic mullite sol as raw materials. SiC interfacial coatings were deposited by polycarbosilane infiltration and pyrolysis before sol-gel process. The as-fabricated composites showed 285.7MPa in flexural strength, relatively close to 277.6MPa of those without coatings. After treated at 1300°C and 1500°C in Ar atmosphere for 1h, the retention rates of flexural strength were 80.0% and 69.9%, respectively, which showed a great improvement compared to the composites without coatings. This was attributed to the prevention of carbothermal reduction between carbon fiber and matrix by SiC coatings.

Hai Tao Liu

Papers

Thermochromic VO2 Thin Film Prepared by Post Annealing Treatment of V2O5 Thin Film

Fabrication and Properties of 3D-Cf/Mullite Composites with SiC Interfacial Coatings

Preparation and Mechanical Properties of 3D‐Cf/Mullite Composites Fabricated by Sol‐Gel Process