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Register a new userHigh Infrared Reflectance Modulation in VO2 Films Synthesized on Glass and ITO coated Glass substrates using Atmospheric Oxidation of Vanadium
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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 switching values of ~76% and ~79% are obtained on the respective substrates, which are among the highest reported values. Using the reflectance data, we extract VO2 complex refractive index in infrared wavelengths, in both the insulating and metallic phases. The extracted refractive index shows good agreement with VO2 synthesized using other methods. This demonstration of high optical reflectance switching in VO2 thin films, grown on low cost glass and ITO coated glass substrates, using a simple low thermal budget process will aid in enhancing VO2 applications in the optical domain.
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Vanadium dioxide is a complex oxide material, which shows large resistivity and optical reflectance change while transitioning from the insulator to metal phase at ~68 {deg}C. In this work, we use a modified atmospheric thermal oxidation method to oxidize RF-sputtered Vanadium films. Structural, surface-morphology and phase-transition properties of the oxidized films as a function of oxidation duration are presented. Phase-pure VO2 films are obtained by oxidizing ~130 nm Vanadium films in short oxidation duration of ~30 seconds. Compared to previous reports on VO2 synthesis using atmospheric oxidation of Vanadium films of similar thickness, we obtain a reduction in oxidation duration by more than one order. Synthesized VO2 thin film shows resistance switching of ~3 orders of magnitude. We demonstrate optical reflectance switching in long-wave infrared wavelengths in VO2 films synthesized using atmospheric oxidation of Vanadium. The extracted refractive index of VO2 in the insulating and in the metallic phase is in good agreement with VO2 synthesized using other methods. The considerable reduction in oxidation time of VO2 synthesis while retaining good resistance and optical switching properties will help in integration of VO2 in limited thermal budget processes, enabling further applications of this phase-transition material.
Vanadium dioxide (VO2) is a phase transition material that undergoes a reversible insulator-metal phase transition at ~ 68 C. Atmospheric pressure thermal oxidation (APTO) of vanadium (V) is a simple VO2 synthesis method in which V thin film is oxidized in open air. For an optimum oxidation duration, VO2 films are obtained with good phase transition properties. We recently reported a modified APTO process using a step temperature profile for oxidation (Thin Solid Films 706, 138003 (2020)). We demonstrated an ultra-low thermal budget synthesis of VO2 thin films with good electrical and optical phase transition properties. For a 130 nm room-temperature RF sputtered V thin film, an optimum oxidation duration of ~ 30 s was obtained. In this work, we study how the starting V film thickness and deposition temperature affects the optimum oxidation duration. V thin films of varying thickness (15-212 nm) and 120 nm thick V films with varying deposition temperature (~27-450 C) are prepared using RF magnetron sputtering. These films are oxidized for different oxidation durations and characterized using Raman and four-probe measurements to find the optimum oxidation duration for each deposition condition. We find that the optimum oxidation duration increases with the increase in V film thickness and V deposition temperature. We model the effect of V film thickness and deposition temperature on the optimal oxidation time using a parabolic law which can be used to obtain the optimal oxidation times for intermediate V thicknesses/deposition temperatures.
The optical/infrared properties of films of vanadium dioxide (VO2) and vanadium sesquioxide (V2O3) have been investigated via ellipsometry and near-normal incidence reflectance measurements from far infrared to ultraviolet frequencies. Significant changes occur in the optical conductivity of both VO2 and V2O3 across the metal-insulator transitions at least up to (and possibly beyond) 6 eV. We argue that such changes in optical conductivity and electronic spectral weight over a broad frequency range is evidence of the important role of electronic correlations to the metal-insulator transitions in both of these vanadium oxides. We observe a sharp optical transition with possible final state (exciton) effects in the insulating phase of VO2. This sharp optical transition occurs between narrow a1g bands that arise from the quasi-one-dimensional chains of vanadium dimers. Electronic correlations in the metallic phases of both VO2 and V2O3 lead to reduction of the kinetic energy of the charge carriers compared to band theory values, with paramagnetic metallic V2O3 showing evidence of stronger correlations compared to rutile metallic VO2.
Highly flexible electromagnetic interference (EMI) shielding material with excellent shielding performance is of great significance to practical applications in next-generation flexible devices. However, most EMI materials suffer from insufficient flexibility and complicated preparation methods. In this study, we propose a new scheme to fabricate a magnetic Ni particle/Ag matrix composite ultrathin film on a paper surface. For a ~2 micro meter thick film on paper, the EMI shielding effectiveness (SE) was found to be 46.2 dB at 8.1 GHz after bending 200,000 times over a radius of ~2 mm. The sheet resistance (Rsq) remained lower than 2.30 Ohm after bending 200,000 times. Contrary to the change in Rsq, the EMI SE of the film generally increased as the weight ratio of Ag to Ni increased, in accordance with the principle that EMI SE is positively related with an increase in electrical conductivity. Desirable EMI shielding ability, ultrahigh flexibility, and simple processing provide this material with excellent application prospects.
This work reports the strain effect on the electrical properties of highly doped n-type single crystalline cubic silicon carbide (3C-SiC) transferred onto a 6-inch glass substrate employing an anodic bonding technique. The experimental data shows high gauge factors of -8.6 in longitudinal direction and 10.5 in transverse direction along the [100] orientation. The piezoresistive effect in the highly doped 3C-SiC film also exhibits an excellent linearity and consistent reproducibility after several bending cycles. The experimental result was in good agreement with the theoretical analysis based on the phenomenon of electron transfer between many valleys in the conduction band of n-type 3C-SiC. Our finding for the large gauge factor in n-type 3C- SiC coupled with the elimination of the current leak to the insulated substrate could pave the way for the development of single crystal SiC-on-glass based MEMS applications.
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