Technique for Creating\n3D Ordered Colloidal Crystals\nwith Hexagonal Close Packing and Uniform Thickness over a Large Area

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