Electric field-assisted metal insulator transition in vanadium dioxide (VO2) thin films: optical switching behavior and anomalous far-infrared emissivity variation
Résumé
We present the vanadium dioxide (VO 2) thin films deposition using e-beam evaporation of a vanadium target under oxygen atmosphere on different substrates (sapphire, Si, SiO 2 /Si…) and we focus on their electrical and optical properties variations as the material undergoes a metal-insulator transition under thermal and electrical stimuli. The phase transition induces extremely abrupt changes in the electronic and optical properties of the material: the electrical resistivity increases up to 5 orders of magnitude while the optical properties (transmission, reflection, refractive index) are drastically modified. We present the integration of these films in simple planar optical devices and we demonstrate electrical-activated optical modulators for visible-infrared signals with high discrimination between the two states. We will highlight a peculiar behavior of the VO 2 material in the infrared and far infrared regions (2-20 m), namely its anomalous emissivity change under thermal-end electrical activation (negative differential emittance phenomenon) with potential applications in active coatings for thermal regulation, optical limiting or camouflage coatings.
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