Surface‐Guided Crystallization of Xanthine Derivatives for Optical Metamaterial Applications
Angelica Niazov‐Elkan, Margarita Shepelenko, Lotem Alus, Miri Kazes, Lothar Houben, Katya Rechav, Gregory Leitus, Anna Kossoy, Yishay Feldman, Leeor Kronik, Peter G. Vekilov, Dan Oron
Abstract
Numerous bio-organisms employ template-assisted crystallization of molecular solids to yield crystal morphologies with unique optical properties that are difficult to reproduce synthetically. Here, a facile procedure is presented to deposit bio-inspired birefringent crystals of xanthine derivatives on a template of single-crystal quartz. Crystalline sheets that are several millimeters in length, several hundred micrometers in width, and 300-600 nm thick, are obtained. The crystal sheets are characterized with a well-defined orientation both in and out of the substrate plane, giving rise to high optical anisotropy in the plane parallel to the quartz surface, with a refractive index difference Δn ≈ 0.25 and a refractive index along the slow axis of n ≈ 1.7. It is further shown that patterning of the crystalline stripes with a tailored periodic grating leads to a thin organic polarization-dependent diffractive meta-surface, opening the door to the fabrication of various optical devices from a platform of small-molecule based organic dielectric crystals.