Determination of Porosity of TiO[sub 2] Films from Reflection Spectra

Reflection spectra of films on titanium substrates were measured at different incident angles of visible light (wavelength 400-800 nm). Porosities of the films were estimated from the refractive indexes of the films which were determined from the dependency of the interference wavelength on the incident angle. Porous films formed in NaOH solutions mostly exhibit refractive indexes smaller than 2.1, indicating that the porosity is greater than 30%. As the porosity increases, the refractive index becomes less dependent on wavelength. The porosities determined from reflection spectra are in good agreement with the pore space ratios obtained by the density profile analysis of scanning electron microscopic images.