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Illustration of the structural symmetries of 2D patterns obtained by elastic deformation of a PDMS membrane with a square lattice of circular holes. (a) SEM image of the original PDMS membrane with hole diameter , pitch , and depth . [(b) and (c)] SEM images of “diamond plate” patterns imprinted from (b) PEGDMA and (c) nanoparticle assemblies, respectively. (b) The EGDMA monomers mixed with photoinitiator, Darocur 1173 (Ciba Specialty Chemicals Inc.), were applied to the PDMS membrane, which swelled the PDMS and deformed the holes into the diamond plate structure. The deformed pattern was captured by photo-cross-linking under UV light (dose of ), followed by peeling off of the solidified film for characterization. (c) A solution of nanoparticles suspended in toluene (2.5% w/v) is deposited onto the PDMS membrane. Nanoparticles convectively assembled on the PDMS membrane while it was swollen by toluene, capturing the deformed pattern. The nanoparticle film was then transferred to another substrate by microcontact printing for characterization. [(d)–(f)] SEM images of nanoparticle assemblies from the stretched PDMS membranes at a uniaxial strain level of (d) , (e) , and (f) . Scale bars: .
SEM images of a honeycomb structure with localized diamond plate patterns. (a) Overview. (b) Close-up. The PDMS membrane was treated with oxygen plasma (PDC-001, Harrick Scientific Products, Inc.) at a power of 100 W for 30 min through a copper grid, followed by swelling with nanoparticle/toluene solution. Since the oxidized region was not swollen by toluene, diamond plate pattern only appeared in the nonoxidized regions that were masked by the copper grid.
(Color online) Summary of PBG calculation results of Si posts with various symmetries. and is the light velocity in vacuum. Inset: SEM images of epoxy pillar array replica molded from undeformed PDMS membrane,14 PEGDMA, and nanoparticle assemblies imprinted from the deformed PDMS membranes, corresponding to those shown in Fig. 1. Scale bars: .
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