Silica single-layer inverse opal films: large-area crack-free fabrication and the regulation of transmittance in the visible region

Abstract

Crack-free large-area SiO₂ single-layer inverse opal (IO) films, which possess typical circular holes on their surface similar to an “inverse moth's eye” structure, were designed based on the “dynamic hard-template infiltration strategy” by using a wide range of sizes of sacrificial polystyrene (PS) sphere templates, ranging from 220 to 930 nm. According to this strategy, a dynamic opal single-layer film of PS spheres is firstly self-assembled on the surface of water, followed by the infiltration of SiO₂ precursor sol from underneath into the voids of the PS opal template. The obtained floating SiO₂/PS opal composite film is deposited on high alumina silicate glass substrates, followed by calcination at 680 °C to yield single-layer SiO₂ IO films with various pore sizes presenting a surface configuration similar to an inverse moth's eye structure. The effects of the porous structure on transmittance in the visible region are investigated. The pore depth, pore wall thickness and pore size concurrently play important roles in transmittance. It has been found that the transmittance increases as the opal period decreases and the intersection point between the transmittance spectra of the single-layer SiO₂ IO films and that of the bare substrate red shifts as the pore size increases. To our knowledge, this is the first time that the fabrication of silica single-layer IO films having an inverse moth's eye structure and the relationship between their porous structure and optical properties in the visible region have been reported.