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

Abstract

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.