Vapor Deposition of Hybrid Organic–Inorganic Dielectric Bragg Mirrors having Rapid and Reversibly Tunable Optical Reflectance

Rapid (0.3 s) and reversible biomimetic response of flexible dielectric mirrors was achieved by alternating inorganic (titania) and organic (poly(2-hydroxyethyl methacrylate, pHEMA) layers. Tunable reflectance bands in the visible range resulted from water swelling of the un-cross-linked pHEMA layers, without affecting the optical thickness of the high refractive index inorganic layer, which is in precise analogy to the structural color changing mechanism employed by many natural species. Larger refractive index contrast than accessible for all organic mirrors allow the desired reflectivity to be achieved with fewer layers and hence less overall thickness. The observed optical responses quantitatively match model predictions and are completely reversible. There is no loss in reflectivity intensity upon swelling. Hybrid heterostructures were grown within a single hot-wire chemical vapor deposition (CVD) chamber, resulting in smooth and uniform nanoscale layers of high interfacial quality. To the best of our knowledge, this is the first ever combination of an inorganic thin film with a fully functional polymer thin film having interfacial smoothness at the nanoscale. The room-temperature solventless HWCVD process is scalable to large area roll-to-roll deposition and is compatible with deformable substrates such as paper and plastic.