Fabrication and Light-Transmission Properties of Monolayer Square Symmetric Colloidal Crystals via Controlled Convective Self-assembly on 1D Grooves

method to prepare high-quality monolayer square-lattice colloidal crystals has not been reported yet. In this Communication, we report our study of self-assembly of colloidal polystyrene (PS) spheres on a 1D-patterned substrate. Previous studies showed that colloidal structures formed on a 1D-patterned substrate are highly sensitive to the ratio between sphere diameter (d) and groove period (p). [10a] Here, we explore other factors that could have a key influence on the formation of 2D square symmetric colloidal crystals using a 1D-patterned substrate. By introducing an experimental cell that allows simultaneous actions and strong competition of forces on colloids exerted by the suspension drying front and the patterned substrate, we have identified distinct effects of convective assembly on the growth of colloidal crystal by controlling the angle orientation (a) between the colloidal suspension drying front and 1D template grooves. We find that those experimental configurations with a having a large deviation from a = 45° will introduce a large amount of defects during the self-assembly process. We demonstrate that, by controlling the angle a in the vicinity of 45°, convective assembly in a cell with a 1D groove template as the substrate can induce a highly ordered 2D square-lattice colloidal crystal with a minimum density of defects. The long-range ordering of the prepared 2D square symmetric colloidal crystals is characterized by electron and optical microscopy, laser diffraction, and light transmission. Transmission spectra of the prepared square symmetric colloidal crystal are measured at normal and off-normal incidence under different polarizations and are shown to be in good agreement with theoretical calculations.