Abstract
Photonic polystyrene (PS) opals with face-centered cubic structure were fabricated by convective evaporation. The influences of substrate and its physical properties, as well as deposition conditions were investigated. It is shown that the surface roughness must be less than about 30% of the bead diameter to form well- ordered opals, rendering substrates such as glass, ITO and quartz superior to thick Kapton, ordinary tape, thermal release semiconductor tape, plastic and hydrophilic plastic HHNW W (Kemafoil). Periodic stripe-like structures were found to form perpendicular to the growth direction defined by the receding meniscus of the solution front when the PS concentration is lower than 1.0 w/v%. Finally, we present the principles and results of using soft sacrificial layer deposited on quartz substrates to fabricate free standing inverse opal structures.
Highlights
Artificial opals are self-assembled face-centered cubic structures of spherically shaped beads, which show interesting applications as photonic band gap materials [1]
Inverse opals are photonic crystals consisting of fcc packed voids embedded in a high refractive index material matrix. [2,3,4]. such structures have been used to enhance the efficiency of photocatalytic materials [5,6,7], and motivates further studies to improve the deposition process and the quality of the template opals [812]
It was possible to deposit opals on quartz, indium tin oxide (ITO), thin Kapton film and glass, which were pre-treated with Decon90 to give them hydrophilic wetting properties
Summary
Artificial opals are self-assembled face-centered cubic (fcc) structures of spherically shaped beads, which show interesting applications as photonic band gap materials [1]. Convective evaporation is a common method to make artificial opals [13; 14], and has been used to deposit square centimeters of polystyrene or silica beads. Due to the strainexerted on the PS beads as the liquid is evaporated from the wet structure, opals tend to crack during the drying process and form millimeter-sized domains [20]. We show results of PS self-assembly of opal structures on soft sacrificial layers deposited on quartz substrates, which enables fabrication of free-standing opal structures which can reduce stress in the film upon drying facilitating larger domains of well-ordered structures
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