Anna V. Shneidman

Tuning and Freezing Disorder in Photonic Crystals using Percolation Lithography.

Although common in biological systems, synthetic self-assembly routes to complex 3D photonic structures with tailored degrees of disorder remain elusive. Here we show how liquids can be used to finely control disorder in porous 3D photonic crystals, leading to complex and hierarchical geometries. In these optofluidic crystals, dynamically tunable disorder is superimposed onto the periodic optical structure through partial wetting or evaporation. In both cases, macroscopic symmetry breaking is driven by subtle sub-wavelength variations in the pore geometry. These variations direct site-selective infiltration of liquids through capillary interactions. Incorporating cross-linkable resins into our liquids, we developed methods to freeze in place the filling patterns at arbitrary degrees of partial wetting and intermediate stages of drying. These percolation lithography techniques produced permanent photonic structures with adjustable disorder. By coupling strong changes in optical properties to subtle differences in fluid behavior, optofluidic crystals may also prove useful in rapid analysis of liquids.

Bio-inspired tunable disorder in a 3D photonic crystal via highly controlled partial wetting and drying

We use highly controlled partial wetting in chemically encoded 3D photonic crystals to study tunable disorder in structurally colored systems. Our experimental and FDTD analyses also guide our design of a colorimetric indicator for organic liquids.

Nanocrystalline Precursors for the Co-Assembly of Crack-Free Metal Oxide Inverse Opals

Inorganic microstructured materials are ubiquitous in nature. However, their formation in artificial self-assembly systems is challenging as it involves a complex interplay of competing forces during and after assembly. For example, colloidal assembly requires fine-tuning of factors such as the size and surface charge of the particles and electrolyte strength of the solvent to enable successful self-assembly and minimize crack formation. Co-assembly of templating colloidal particles together with a sol-gel matrix precursor material helps to release stresses that accumulate during drying and solidification, as previously shown for the formation of high-quality inverse opal (IO) films out of amorphous silica. Expanding this methodology to crystalline materials would result in microscale architectures with enhanced photonic, electronic, and catalytic properties. This work describes tailoring the crystallinity of metal oxide precursors that enable the formation of highly ordered, large-area (mm2 ) crack-free titania, zirconia, and alumina IO films. The same bioinspired approach can be applied to other crystalline materials as well as structures beyond IOs.

Uniform and large volume microwave magnetic coupling to NV centers in diamond using split ring resonators

A microwave resonator for uniform coupling of microwave magnetic field into NV centers in diamond over a mm3 volume with an average Rabi frequency of 16 MHz with a 5% variance for 0.5 W microwave power is reported.

Wetting in color: from photonic fingerprinting of liquids to optical control of liquid percolation

We provide an overview of our recent advances in the manipulation of wetting in inverse-opal photonic crystals. Exploiting photonic crystals with spatially patterned surface chemistry to confine the infiltration of fluids to liquidspecific spatial patterns, we developed a highly selective scheme for colorimetry, where organic liquids are distinguished based on wetting. The high selectivity of wetting, upon-which the sensitivity of the response relies, and the bright iridescent color, which disappears when the pores are filled with liquid, are both a result of the highly symmetric pore structure of our inverse-opal films. The application of horizontally or vertically orientated gradients in the surface chemistry allows a unique response to be tailored to specific liquids. While the generic nature of wetting makes our approach to colorimetry suitable for applications in liquid authentication or identification across a broad range of industries, it also ensures chemical non-specificity. However, we show that chemical specificity can be achieved combinatorially using an array of indicators that each exploits different chemical gradients to cover the same dynamic range of response. Finally, incorporating a photo-responsive polyelectrolyte surface layer into the pores, we are able to dynamically and continuously photo-tune the wetting response, even while the film is immersed in liquid. This in situ optical control of liquid percolation in our photonic-crystal films may also provide an error-free means to tailor indicator response, naturally compensating for batch-to-batch variability in the pore geometry.

Highly selective colorimetric differentiation of organic liquids in 3D photonic crystals

We present a colorimetric indicator that distinguishes organic liquids, projecting small differences in wettability into visually distinct color patterns. Photonic crystals serve as both selective carriers for liquids and sources of responsive color.