Fabrication and optical characterization of a TiO2 thin film on a silica microsphere

We have fabricated a uniform TiO2 thin film on a silica microsphere by using the so-called sol–gel reaction. Characterization of the TiO2 thin film was carried out by scanning electron microscopy, Raman scattering, and the attenuated-total-reflection (ATR) method. We have observed optical resonances of microspheres with and without the TiO2 thin film by using the ATR method, which allowed us to evaluate optically the thickness and the refractive index of the TiO2 thin film from the resonance due to excited whispering gallery modes, which are resonance modes inherent of microspheres.