Rapid fabrication of high-quality bare silica monolayer and multilayers at the water/air interface

We report on a rapid and efficient method to self-assemble high-quality monolayer or multilayers of bare silica microsphere (MS) at the water/air interface. The key to our method is forming an ultra-thin 1-butanol layer achieved by using the mixed suspension with a proper volume ratio of ethanol and 1-butanol (2:1) on the water surface. This ultra-thin 1-butanol can deliver, confine and keep the movement of the SiO2 MS at the air/water interface throughout the self-assembly process, which is of crucial importance for achieving the high-quality of the assembled monolayer. By our method, the hexagonal-close-packed arrangement monolayers of bare SiO2 MS with millimeter-sized (similar to mm) single-domain regions are successfully fabricated for different sizes (diameters: 300, 480, 730, and 990 nm). In addition, the multilayers fabricated by the layer-by-layer transferring technique present the typical photonic bandgap materials feature in the measured transmission spectra. The fabricated high-quality monolayer or multilayers of bare SiO2 MS could be compatible with the high-temperature material grown process and may find potential applications in optoelectmnics and photocatalysis.