Generalized fabrication of monolayer nonclose-packed colloidal crystals with tunable lattice spacing

Here, we report a simple colloidal transfer technology that enables scalable fabrication of monolayer nonclose-packed silica colloidal crystals on a large variety of substrates. Two-dimensional colloidal crystals with an unusual nonclose-packed structure are first assembled on silicon wafers by a spin-coating technique. A poly(vinyl alcohol) (PVA) film cast upon the spin-coated colloidal crystal is used to transfer the nonclose-packed particle arrays onto various substrates. The lattice spacing of the transferred monolayer colloidal crystal can easily be adjusted by thermally treating the PVA-silica spheres composite film for varied durations. We also have demonstrated the templating fabrication of periodic arrays of gold nanodots using a transferred monolayer nonclose-packed colloidal crystal as a structural template. The resultant plasmonic array exhibits high surface-enhanced Raman scattering enhancement factor (~3.8 × 10(7)) for adsorbed benzenethiol molecules.