Optical Properties and Microstructures of Colloidal Crystalline Arrays

Colloidal crystalline arrays are three dimensionally periodic lattices of self-assembled monodisperse colloidal spheres. We have demonstrated the synthesis of silica or polystyrene spheres uniformly coated with titania nanosheets and the fabrication of these spheres into close-packed colloidal crystalline arrays. The Bragg diffraction peak of the colloidal crystalline array shifted to longer wavelengths with increasing thickness of titania nanosheets layers. Angle-resolved reflection spectra measurements showed that this red shift was caused by increasing the mean effective refractive index n_eff of this crystalline lattice without changing interplanar spacing d₁₁₁ with increasing thickness of titania nanosheets layers.