3D-chiral transparent single-crystal silicon metasurface for visible light

We report a chiral dielectric metasurface with regular 3D nanorelief patterned by focused ion beam in a 300 nm thin single-crystal silicon film on sapphire. Upon annealing, the metasurface features a high transparency along with a circular dichroism and an optical activity reaching 0.5 and 20° respectively in the visible range, possesses crystal-grade hardness, chemical inertness of glass, and thermal stability of up to 1000° C. The developed technique paves the way for new types of 3D-structured silicon meatsurfaces and metadevices.