Large-scale assembly of periodic nanostructures with metastable square lattices

This article reports a simple and scalable spin-coating technique for assembling non-close-packed colloidal crystals with metastable square lattices over wafer-scale areas. The authors observe the alternate formation of hexagonal and square diffraction patterns when the thickness of the colloidal crystals is gradually reduced during spin coating. No prepatterned templates are needed to induce the formation of the resulting metastable crystals with square arrangement. This bottom-up technology also enables the large-scale production of a variety of squarely ordered nanostructures that are consistent with the industry-standard rectilinear coordinate system for simplified addressing and circuit interconnection. Broadband moth-eye antireflection gratings with square lattices have been fabricated by using the shear-aligned colloidal monolayers as structural templates. Optical reflection measurement shows the squarely ordered arrays exhibit lower reflection than the nature-inspired hexagonal arrays with the similar structural parameters.