TiO(2) metasurfaces: From visible planar photonics to photochemistry

TiO(2) metasurfaces have been intensively studied in the past few years. To date, the TiO(2) metadevices only used their high reflective index (n). The controllable light extinction coefficient (k) of TiO(2) has not been exploited yet. Here, we converted TiO(2) metasurfaces to black TiO(2) metasurfaces and explored their new opportunities in photochemistry. A complementary metal oxide semiconductor (CMOS)–compatible technique has been developed to reversibly and precisely control the absorption of TiO(2) metasurfaces without spoiling their internal nanostructures. Consequently, two types of black TiO(2) metasurfaces were realized for photochemical experiments. The metasurface with an ultrawide absorption band can substantially enhance the white light absorption and accelerate the solar-based photochemistry process by a factor of 18.7. The other metasurface with an absorption band of <20 nm only responded to the resonant wavelengths, making the photochemistry process capable of being monitored in real time. In addition, the reversible switch between normal and black states makes TiO(2) metasurfaces suitable for dynamic metadevices as well.