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Evaporation‐induced self‐assembly of colloidal particles is one of the most versatile fabrication routes to obtain large‐area colloidal crystals; however, the formation of uncontrolled "drying cracks" due to gradual solvent evaporation represents a significant challenge of this process. While several methods are reported to minimize crack formation during evaporation‐induced colloidal assembly, here an approach is reported to take advantage of the crack formation as a patterning tool to fabricate microscopic photonic structures with controlled sizes and geometries. This is achieved through a mechanistic understanding of the fracture behavior of three different types of opal structures, namely, direct opals (colloidal crystals with no matrix material), compound opals (colloidal crystals with matrix material), and inverse opals (matrix material templated by a sacrificial colloidal crystal). This work explains why, while direct and inverse opals tend to fracture along the expected {111} planes, the compound opals exhibit a different cracking behavior along the nonclose‐packed {110} planes, which is facilitated by the formation of cleavage‐like fracture surfaces. The discovered principles are utilized to fabricate photonic microbricks by programming the crack initiation at specific locations and by guiding propagation along predefined orientations during the self‐assembly process, resulting in photonic microbricks with controlled sizes and geometries. [ABSTRACT FROM AUTHOR]

Photonic Microbricks: Fabrication of Photonic Microbricks via Crack Engineering of Colloidal Crystals (Adv. Funct. Keywords: colloidal crystals; fracture; nano/microfabrication; self-assembly EN colloidal crystals fracture nano/microfabrication self-assembly 1 1 1 06/27/20 20200625 NES 200625 In article number 1908242, Ling Li and co-workers provide a mechanistic understanding of crack formations during the evaporation-induced self-assembly of colloidal crystals, which allows for rational controlling of the location and orientation of cracks for fabricating photonic microstructures with controlled geometries and sizes. Colloidal crystals, fracture, nano/microfabrication, self-assembly. [Extracted from the article]