Abstract
We have been sputtering TiO2 and SiO2 for use in wide-band anti-reflection coatings on glass. We have made a study of the the optical properties of single material depositions of each of the constituent films on Corning 7059 and Silicon Wafer substrates. We have also taken some of the TiO2 depositions and deposited a SiO2 film on top of them during the same run in which the individual SiO2 sample was deposited. We are interested in knowing if the optical properties of the TiO2 or the SiO2 are affected by the deposition of SiO2 on top of the TiO2. Optical studies have been made of the six types of samples: SiO2, TiO2, and SiO2/TiO2 on the 7059 glass and Silicon wafers. Data has been taken with a Variable Angle Spectroscopic Ellipsometer (VASE ref. 1) from 300nm to 1000nm in wavelength and at a variety of angles of incidence from 50 to 80 degrees. In addition transmission and reflection data near normal incidence has been taken using a VW reflection accessory on a CARY 17DI dual-beam spectrophotometer from 350 nm to 750 nm. First the TiO2 ellipsometric data was analysed. The TiO2 was sufficiently transparent in the visible and near infrared that it was possible to set the extinction coefficient to zero and solve for the index of refraction and physical thickness of the sample. Having established a value for the physical thickness, the ellipsometric data, Psi and Delta, was used to find the value of n and k at each wavelength by a recursive process. After making many studies of several different samples of TiO2, it was found that the simplest way to characterize a particular sample of TiO2 was as a mixture of two extreme material types labeled TiO2 (Low Index) and TiO2 (High Index). We have used the effective medium approximation (EMA) to combine them and use the volume fraction of the TiO2 (Low Index) that is mixed into the TiO2 (High Index) as the adjustable parameter, vf10.
© 1992 Optical Society of America
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