Volumetric Patterning of Gels via Super Resolved Interference Lithography

Here we demonstrate the volumetric patterning of photochromic gels by super-resolution interference lithography. Judicious choice of solvent, which impacts the photophysics of the photochromic switch, and ensuring the swollen nature of the gel, facilitate the highly parallelized patterning of thick gels via two-color interference lithography using cost-effective UV LEDs and visible-light laser diodes. Based on the predictions of a simple photokinetic model of the reversibly saturable writing process for contrast and feature size widths on the solvent-dependent thermal back reaction constant, ethylene glycol is chosen as the solvent. Polyacrylamide gels designed to maximize swelling in ethylene glycol are postfunctionalized with spirothiopyran photoswitches and simultaneously exposed to a featureless illumination of UV light and a standing wave of green light, resulting in volumetric patterning of films that are tens of microns in thickness. Features with super-resolved critical dimensions ∼ 90 nm are achieved. Resolutions of ∼ 220 nm are achieved by phase-shifted double exposures. Reducing exposure times from 80 s to 100 ms while keeping dose constant comes at the cost of reduced contrast.