Engineering thermochromic properties with plasmonics, quantum dots, and 2D materials.

For temperature-sensing applications, it is desirable to obtain strong thermochromic response in visible spectral range. We experimentally evaluate possible enhancements of sensitive thermochromic materials based on vanadium oxide (VO_x) by nanophotonic engineering. First, we compare various growth methods, including a deposition and annealing of thin films and an electrochemical growth of single crystals. Second, we perform macro- and microscale temperature-dependent optical measurements of materials with different composition. Then, we demonstrate an enhanced thermochromic behavior by the application of plasmonic and quantum materials. With periodic gold hemispherical structures atop VO₂ crystals, the optical contrast at the VO₂ phase transition from semiconductor to metal is increased by ≈ 15 % at visible/near-infrared wavelengths. The enhancement is due to the localized surface plasmon resonances of gold particles and can be described within the Maxwell-Garnett effective medium theory. We also discuss other approaches, including the coupling of two dimensional materials and colloidal quantum dots, to further tailor temperature-dependent optical response of thermochromic materials. Finally, we introduce possible applications focusing on nanoscale temperature sensing.