Preparation of Monodisperse SiO_2/TiO_2/SiO_2 Multiply Coated Submicrospheres

The monodisperse SiO2/TiO2/SiO2 multiply coated submicrospheres with uniform size, high refractive index and easily assembling property for constructing photonic crystals were prepared. The multilayer complex submicrosphere consisted of a colloidal silica sphere as core, a thick titania coating, and a outermost, thin coating of silica. Monodisperse colloidal silica spheres with 200nm in diameter were synthesized through the hydrolysis of tetraethyl orthosilicate(TEOS) in aqueous ethanol solutions with ammonia as catalyst. The titania coating about 40nm thick on silica cores was formed by the hydrolysis of titanium n-butoxide(TBOT). The hydrolysis of tetraethyl orthosilicate (TEOS) was still used to get the outermost silica coating about 10nm thick on titania coated silica submicrospheres. The SiO2, TiO2/SiO2 and SiO2/TiO2/SiO2 submicro- spheres were characterized with transmission electron microscopy(TEM), energy dispersive X-ray fluorescence spectroscopy(EDS), and the method of gravity sedimentation separately.