Controlling metal–insulator transitions in reactively sputtered vanadium sesquioxide thin films through structure and stoichiometry

We present a study of $$\hbox {V}_{2}\hbox {O}_{3}$$ V 2 O 3 thin films grown on c-plane $$\hbox {Al}_{2}\hbox {O}_{3}$$ Al 2 O 3 substrates by reactive dc-magnetron sputtering. Our results reveal three distinct types of films displaying different metal–insulator transitions dependent on the growth conditions. We observe a clear temperature window, spanning 200 $$^{\circ }$$ ∘ C, where highly epitaxial films of $$\hbox {V}_{2}\hbox {O}_{3}$$ V 2 O 3 can be obtained wherein the transition can be tuned by controlling the amount of interstitial oxygen in the films through the deposition conditions. Although small structural variations are observed within this window, large differences are observed in the electrical properties of the films with strong differences in the magnitude and temperature of the metal–insulator transition which we attribute to small changes in the stoichiometry and local strain in the films. Altering the sputtering power we are able to tune the characteristics of the metal–insulator transition suppressing and shifting the transition to lower temperatures as the power is reduced. Combined results for all the films fabricated for the study show a preferential increase in the a lattice parameter and reduction in the c lattice parameter with reduced deposition temperature with the film deviating from a constant volume unit cell to a higher volume.

Oxygen Storage in Transition Metal-Doped Bixbyite Vanadium Sesquioxide Nanocrystals

<p>Bixbyite vanadium sesquioxide (V₂O₃) is a metastable polymorph of vanadium oxide that has been shown to have a significant oxygen storage capacity with very low temperature oxidation onset. In this work, bixbyite V₂O₃ nanocrystals were synthesized with titanium and manganese dopants. Doped materials with varied dopant concentration were synthesized, and all were incorporated as aliovalent metal ions. The oxygen storage capacity of these nanocrystal materials was evaluated over ten oxidation and reduction cycles. It was found that over these ten cycles, the oxygen storage capacity of all the materials fell drastically. <i>In situ</i> X-ray diffraction evidence shows that manganese-doped materials degrade into an amorphous manganese-containing vanadate, while titanium-doped materials form crystalline degradation products. In all cases, this degradation causes an increase in the minimum mass achieved during oxygen release, indicating irreversible oxidation. </p>

Oxygen Storage in Transition Metal-Doped Bixbyite Vanadium Sesquioxide Nanocrystals

<p>Bixbyite vanadium sesquioxide (V₂O₃) is a metastable polymorph of vanadium oxide that has been shown to have a significant oxygen storage capacity with very low temperature oxidation onset. In this work, bixbyite V₂O₃ nanocrystals were synthesized with titanium and manganese dopants. Doped materials with varied dopant concentration were synthesized, and all were incorporated as aliovalent metal ions. The oxygen storage capacity of these nanocrystal materials was evaluated over ten oxidation and reduction cycles. It was found that over these ten cycles, the oxygen storage capacity of all the materials fell drastically. <i>In situ</i> X-ray diffraction evidence shows that manganese-doped materials degrade into an amorphous manganese-containing vanadate, while titanium-doped materials form crystalline degradation products. In all cases, this degradation causes an increase in the minimum mass achieved during oxygen release, indicating irreversible oxidation. </p>

Vanadium-Oxide-Based Thin Films with Ultra-High Thermo-Optic Coefficients at 1550 nm and 2000 nm Wavelengths

In this paper, the temperature-dependent dielectric properties of vanadium-sesquioxide-based thin films are studied to assess their suitability for thermally tunable filters at optical communication wavelengths. Spectroscopic ellipsometry is utilized to measure the optical constants of vanadium oxide thin films at temperatures ranging from 25 °C to 65 °C. High thermo-optic coefficients (dn/dTs) were observed. The highest dn/dTs, measured at approximately 40 °C, were −8.4 × 10−3/°C and −1.05 × 10−2/°C at 1550 nm and 2000 nm, respectively.

ULTRA-HIGH SENSITIVITY VANADIUM–VANADIUM SESQUIOXIDE–VANADIUM (V–V2O3–V) SYMMETRIC TUNNEL JUNCTION DIODE

In this paper, a symmetrical MIM tunnel junction diode with a novel material combination, vanadium–vanadium sequioxide–vanadium (V–V2O3–V) is fabricated and electrically characterized. Analysis of the measured current-voltage ([Formula: see text]–[Formula: see text] characteristics of the fabricated MIM diode revealed an ultra-high diode sensitivity of [Formula: see text]9.24[Formula: see text][Formula: see text] at an applied bias of [Formula: see text]0.104[Formula: see text]V. Based on the measured [Formula: see text]–[Formula: see text] characteristics, theoretical predictions were performed showing that the diode’s dynamic resistance can be tuned for matching to coupled antennas, in rectenna structures, whilst maintaining high levels of sensitivities using practically realizable V2O3 insulator thicknesses.