[Determination of optical parameters in thin films by transmittance spectra]

The high tin-doped SiO2 films prepared by CVD will bring some crystals, but sol gel can control the accurate chemical component of the films. So it can produce high tin-doped materials. In the present paper, the tin-doped SiO2 films were prepared by a sol gel dip-coating process on glass substrates at concentrations of 66 mol% and 75 mol%. Then dipping was performed several times to enhance the thickness of the films. The transmittance spectrum was obtained by spectrophotometer. Compared with the films prepared in a thin film on a thick substrate previously, the model here has been modified to describe the transmittance of a thick film (substrate) sandwiched between two thin films (coating method). The authors used the curves method to calculate the film's parameters. The result showed that uhe refractive index of different samples was increased with the wave-length. And the film thickness was about 900 nm.