Technique for Creating 3D Ordered Colloidal Crystals with Hexagonal Close Packing and Uniform Thickness over a Large Area.

Traditional approaches to creating colloidal crystals do not simultaneously achieve uniform thickness, three-dimensional ordering, and large areas of defect-free hexagonal close-packed domains. Only the realization of all these conditions will allow the use of colloidal crystals as templates for fabricating inverse opals with a tunable photonic band gap. Therefore, we propose a novel approach for creating 3D colloidal crystals. It combines the use of the Langmuir-Blodgett (LB) process to form the first layer and sequential spin-coating processes to form all following layers. The original automated LB trough, equipped with a feedback control system for surface pressure control, allowed the formation of a close-packed monolayer across the entire area of a 76 mm substrate, obtaining a defect-free domain area of 3000 μm². As a result of the developed spin-coating technique, bilayer and three-layer colloidal crystals based on polystyrene spheres (1.25 and 1.8 μm) were obtained. Three-dimensional HCP structure covered ≈96.5% of the substrate, and a defect-free domain area was obtained at least 1000 μm². The high degree of 3D ordering was confirmed by the presence of stop bands in the transmission spectra at wavelengths corresponding to Bragg diffraction from parallel planes and a 2D array of spherical particles.