Microsphere Autolithography—A Scalable Approach for Arbitrary Patterning of Dielectric Spheres

Abstract

Patchy particles, i.e., colloidal particles whose surface properties have been modified in predetermined patterns, can serve as building blocks for efficient self-assembly of well-defined, ordered structures. This paper introduces MicroSphere AutoLithography (µSAL), a scalable lithographic method for production of patchy particles with arbitrary patch motifs. This technique leverages dielectric microspheres as both a lithographic substrate and the illuminating optic, using the fact that when a plane wave of light is refracted through a sphere, it produces a circular patch of high-intensity illumination on the back hemisphere. Exposing a collection of microspheres to multiple plane waves, every sphere simultaneously projects identical patterns of illuminated patches onto its own surface. Here, µSAL is demonstrated in barium titanate glass (BTG) microspheres that are coated with a thin (≈40 nm) conformal film of poly(dopamine) acting as the photoresist, fixating the optical pattern into a permanent metal structure through light-induced reduction of silver ions from the liquid suspension. Varying the index of refraction of the BTG spheres and the suspension produces a range of patch sizes and geometries in good agreement with theoretical modeling.