Shear-Assembly of Crack-Free, Mesomorphic Ceramics from Zinc Oxide Nanorods for Waveplates

Abstract

Mesomorphic ceramics include inorganic solids with liquid crystalline superstructures and show great promise as waveplates for high-power lasers. Waveplates require sufficiently thick, birefringent, and uniform films, and mesomorphic ceramics made from shear-assembly of zinc oxide nanorods can offer both transparency and uniform birefringence over large areas. However, cracking occurs during processing of mesomorphic ceramics with a thickness beyond a micrometer. Crack formation impairs optical performance and is attributed to excess in-plane tensile stress generated during film processing. To reduce cracks, mesomorphic ceramic zinc oxide films were prepared using three different methods: (I) A single, sintered blade-coated layer was treated with inorganic precursors. (II) Multiple, thin layers were successively blade-coated and sintered. (III) Multiple coatings were combined for precursor treatment. A 2-μm-thick film with a birefringence of 0.09 and a transparency of >92% was achieved by Method III, and the film behaved as a quarter-waveplate at wavelengths between 700 and 725 nm. This reported method repairs cracks in anisotropic nanoparticle assemblies and enables the fabrication of large aperture optical devices such as ceramic waveplates. Such a processing methodology also benefits diverse applications including thin-film transistors, optoelectronics, and photocatalysis.