Fabrication and optical properties of binary colloidal crystal monolayers consisting of micro- and nano-polystyrene spheres

Self-assembling of binary colloidal crystals (bCCs) consisting of spherical particles with different diameters has been used for monolayer fabrication in glass cells. The procedure involves two crystallization steps. Upon crystallization of a colloidal suspension containing large spheres, a monolayer is formed on the bottom substrate of the cell. Then, a colloidal suspension containing small spheres, which assemble in the interstitial parts between the large spheres, is injected into the cell. The resulting bCC monolayers are characterized using scanning electron microscopy (SEM) and reflection spectroscopy. Reflection spectra reflect the bCC structure and forbidden bands corresponding to the grating constant of the second colloidal crystal. The structure and optical properties of the bCC monolayer can be specified depending on the ratio of the diameters of the spheres. The proposed process for bCC monolayer fabrication is extremely simple, and therefore ideal for practical uses.

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► Binary colloidal crystal (bCC) monolayers are fabricated by a simple process using wide gap glass cells.
► Fabricated bCCs are revealed by SEM observations in detail.
► The reasonable formation mechanism is inferred.
► Reflection spectra of the bCCs are investigated using a microscope.
► With decreasing the diameter ratio of spheres forming the bCC, the selective reflection in the spectrum is sharper.