Three-dimensional arrays formed by monodisperse TiO2 coated on SiO2 spheres

Uniform coatings of TiO2 on monodisperse spheres of silica have been obtained. The resulting particle sizes are within the range 0.4 to 1 mu m. The thickness of the coating can be controlled by adjusting nuclei sizes (silica sphere), reaction times, and water and surfactant concentrations. The TiO2/SiO2 spheres were sedimented to achieve structures with three-dimensional order. Three-dimensional ordered materials with higher refractive index were obtained by transforming the amorphous titania layer to rutile by thermal treatment with improved mechanical rigidity. The sphere composition, quality, and morphology have been assessed by different techniques, (C) 2000 Academic Press.