Opal Crystals: Patterning Hierarchy in Direct and Inverse Opal Crystals (Small 12/2012)

This cover shows an optical image of a SiO2 ‘inverse opal’ fi lm having a combination of crystalline and localized quasi-ordered domains that are grown around a patterned hexagonal array of large posts. The contrast of colors corresponds to individual domains in the highly ordered, close-packed nanoporous film, due to Bragg diffraction as a photonic crystal. In this work, topographically patterned surfaces are designed to control the growth of direct and inverse colloidal photonic crystal films. As such, artificially imposed structures control the crystallographic domain nucleation and orientation, and modify the optical properties of these films. The close-packed colloids are forced to organize themselves around the curved surfaces of the posts, causing the nucleation of small domains. This method provides a bottom-up means of synthesizing complex, multi-layered, hierarchical direct and inverse opal structures with highly controlled optical properties and increased functionality. For more information, please refer to the Full Paper “Patterning Hierarchy in Direct and Inverse Opal Crystals” by J. Aizenberg and co-workers, beginning on page 1904.