Light-Induced Printing of Helical Arrays on Solid Substrates

Chemical structures with helical geometries aligned perpendicularly to the substrate display unique optical, biosensing, catalytic, and mechanical properties but are difficult to produce. At the molecular scale, self-alignment of helices along the surface normal was accomplished for biopolymers with thiol anchors. However, the helical segments had to be pre-assembled and orientational defects were frequent. At the nanoscale, the difficulties are exacerbated because the out-of-plane alignment of nanoscale structures is associated with prohibitively high energy costs. Overcoming the unfavorable thermodynamics by light-guided formation of silver nanocrystallites, the stand-up arrays of homochiral helicoids are produced by illumination with circularly polarized light (CPL). The handedness of the silver helicoids and their polarization spectrum are controlled by the ellipticity and wavelength of the incident photons. CPL-induced printing of centimeter-scale metasurfaces with on-the-fly control of polarization effects was demonstrated using a programmable motorized stage. Substrate versatility and high efficiency of light-to-matter chirality transfer enable rapid engineering of metamaterials with chiral patterns for multiple technologies.