On the determination of the optical constants of very thin metallic films

The application of a recently developed spectrophotometric method for the determination of the complex refractive index h and the physical thickness d of very thin films (d congruent to lambda/50, lambda is the wavelength in VIS and NIR) to Au films deposited on transparent glass substrates is presented. The transmittance T-f, the front side reflectance R-f and the back side reflectance R-f' are used for the estimation of (n) over tilde and d. Utilizing the nanothickness of the films, we derive analytical expressions for R-f; R-f' and T-f, by development of the Abeles characteristic matrix elements up to the 4th order in (n) over tilded/lambda. An optimization procedure is used to estimate h and d. Thus, the problems related to multiple solutions or the lack of any solutions is minimized. For comparison with the h and d thus obtained, variable angle spectroscopic ellipsometry is used as an independent technique.