Vicki Colvin
Department of Chemistry
Rice University
From Opals to Optics: Building Photonic Materials from the Bottom Up
The gemstone opal exhibits a brilliant visible iridescence
due to the regular spacing of sub-micron colloids which comprise its
structure. This natural motif can be replicated in the laboratory,
and artificial opals can be cast as thin films of controlled
thickness using colloidal assembly techniques. This assembly method
is well suited to forming photonic superlattices, which allow the
concentration of optical radiation in particular locations within a
colloidal structure. Numerous solids, ranging from polymers to
metals, can be cast around these assemblies and the colloids
subsequently removed. The macroporous materials that result have
arrays of spherical cavities interconnected by smaller windows. The
diffractive properties of these inside-out structures are even
stronger than the host opal, and can in some cases can possess nearly
complete photonic band gaps at visible wavelengths. In addition,
these sponge-like materials can serve as hosts for further growth of
nanostructured solids with complex architectures. We demonstrate
this using porous PMMA to construct solid, hollow and core-shell
nanospheres in a variety of shapes.