Fabrication and optical properties of a ring-shaped colloidal photonic crystal

The quick fabrication of ring-shaped colloidal photonic crystal was demonstrated on the circle-patterned photoresist substrate by spin-coating, which is promising for practical application. Latex spheres were designed with a hydrophobic core and a hydrophilic shell of poly(styrene-methyl methacrylate-acrylic acid). Scanning Electron Microscopy (SEM) images and reflectance spectra of the as-prepared ring-shaped colloidal photonic crystals were acquired. The influences of spinning speed, latex sphere concentration and different circle-patterned photoresist substrates on the morphology of the ring-shaped colloidal photonic crystal were investigated. The results indicate that the optimal parameters for preparing a ring-shaped colloidal photonic crystal are achieved with a spinning speed of 2000 r/min, a latex sphere concentration of 7.5% and a circle-patterned photoresist structure (diameter: 22.8 µm). The SEM images showed that the latex spheres were almost all deposited at the periphery of the ring and were dispersed with relative order, which was attributed to fast evaporation. This fast self-assembly method for preparing ring-shaped colloidal photonic crystals was achieved by spin-coating and relied on the physical confinement of patterned photoresist substrates and their wettability difference. It will have important applications in optical devices, sensing materials and anti-counterfeiting.