Percolation lithography: Tuning and freezing disorder in 3D photonic crystals using partial wetting and drying

Kavli Affiliate: Anna V. Shneidman

| First 5 Authors: Ian B. Burgess, Navid Abedzadeh, Theresa M. Kay, Anna V. Shneidman, Derek J. Cranshaw

| Summary:

Although complex, hierarchical nanoscale geometries with tailored degrees of
disorder are commonly found in biological systems, few simple self-assembly
routes to fabricating synthetic analogues have been identified. We present two
techniques that exploit basic capillary phenomena to finely control disorder in
porous 3D photonic crystals, leading to complex and hierarchical geometries. In
the first, we exposed the structures to mixtures of ethanol and water that
partially wet their pores, where small adjustments to the ethanol content
controlled the degree of partial wetting. In the second, we infiltrated the
structures with thin films of volatile alkanes and observed a sequence of
partial infiltration patterns as the liquid evaporated. In both cases,
macroscopic symmetry breaking was driven by subtle sub-wavelength variations in
the pore geometry that directed site-selective infiltration of liquids. The
resulting patterns, well described by percolation theory, had significant
effects on the photonic structures’ optical properties, including the
wavelength-dependence and angular dependence of scattering. Incorporating
cross-linkable resins into our liquids, we were able create permanent photonic
structures with these properties by freezing in place the filling patterns at
arbitrary degrees of partial wetting and intermediate stages of drying. These
techniques illustrate the versatility of interfacial phenomena in directing and
tuning self-assembly of aperiodic structures.

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