Multi Spectral Switchable Infra-Red Reflectance Resonances in Highly Subwavelength Partially Oxidized Vanadium Thin Films

Abstract: Phase transition materials are promising for realization of switchable optics. In this work, we show reflectance resonances in the near-infrared and long-wave infrared wavelengths in highly subwavelength partially oxidized Vanadium thin films. These partially oxidized films consist of a multilayer of Vanadium dioxide and Vanadium as shown using Raman spectroscopy and four-probe measurements. As Vanadium dioxide is a phase transition material that shows insulator to metal phase transition at 68 C, the observed infra-red resonances can be switched with temperature into a high-reflectance state. The wavelength of these resonances are passively tunable as a function of the oxidation duration. The obtained reflectance resonance at near-infrared wavelength red shifts from 1.78 um to 2.68 um with increasing oxidation duration while the long-wavelength infrared resonance blue shifts from 12.68 um to 9.96 um. To find the origin of the reflectance resonances, we model the reflectance spectra as a function of the oxidation duration using the transfer matrix method. The presented model captures the dual reflectance resonances reasonably well. These passive wavelength-tunable and switchable resonances with easy to fabricate lithography-free multilayer structure will be useful for multispectral applications such as camouflage, spectral selective microbolometer, and thermal management.