Surface‐Guided Crystallization of Xanthine Derivatives for Optical Metamaterial Applications

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.

Stereochemically Active Lone Pair Leads to Birefringence in the Vacancy Ordered Cs3Sb2Cl9 Perovskite Single Crystals

“…In order to assign the birefringence axes, the crystallographic axes of the single crystal are characterized by the in-plane and out-of-plane XRD measurements, as schematically depicted in Figure a. , The out-of-plane XRD scan revealed that the (114) lattice planes are perpendicular to the elongated surface of the rod (Figure b) suggesting a preferred ⟨114⟩ growth direction along the elongated surface of the rod (Figure c). The in-plane XRD scan reveals that (012) lattice planes are parallel to the elongated surface of the rod (Figure d).…”