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(a) Sketch of the concave structure obtained via soft lithography (not in scale). (b) Scanning electron microscopy (SEM) surface image of PDMS inverse colloidal crystal. (c) SEM detail of the ordered hexagonal array. The bar corresponds to 1 µm. (d) Diffracted light from the hexagonal array of voids on transparent elastomeric substrate. Reproduced from [108] under CC BY 4.0 License.
