Facile Bottom-Up Assembly of Photonic Micropatterns via Surface-Guided Colloidal Crystallization.

Abstract

Photonic micropatterns derived from colloidal self-assembly are highly sought after for next-generation optical and functional devices. However, achieving high optical quality, spatial precision, and stopband tunability with a simple fabrication process remains challenging due to the limitations of conventional top-down techniques. Here, a bottom-up strategy is reported for fabricating high-resolution photonic micropatterns via regioselective heterogeneous nucleation and crystallization of polystyrene particles, directed by surface-dependent nucleation behavior. On strongly charged glass, nucleation is suppressed, while on weakly charged photoresist surfaces, it is promoted via depletion-mediated attraction. Photoresist micropatterns prepared by standard photolithography enable single-step, spatially localized crystal growth without physical confinement. The resulting crystalline grains exhibit uniform orientation and minimal intergrain gaps, displaying intense structural colors. By systematically tuning depletant and salt concentrations, an optimal pair potential well depth is identified that yields superior-quality photonic micropatterns. Full-spectrum color tunability is achieved by varying particle size while maintaining this optimal interaction range. Moreover, bidisperse systems show exclusive crystallization of distinct grain types within a single pattern, enabling in situ color mixing and extended color palettes. Beyond photolithography, that accessible charge-guided patterning is demonstrated using vapor-phase masking, oil stamping, and even fingerprints, highlighting the versatility and scalability of this bottom-up approach.