From a series of ellipsometric measurements it is now possible to obtain uniquely all of the optical parameters of the system; absorbing substrate+nonabsorbing surface film. The method utilizes the fact that the reflectance of such a system at normal incidence remains essentially constant for a small but finite range of surface-film thicknesses. Furthermore, it hinges on the fact that the ellipsometric parameters Δ and ψ, measured on different film thicknesses grown on the same sample, are compatible with only one choice of the complex refractive index n2 +ik2 of the substrate and the refractive index n1 of the film. Measurements on chemically etched samples of silicon yield n2 = 4.052 and k2 = 0.029, in agreement with the results of earlier workers. Measurements on cleaved samples of silicon, on the other hand, reveal that the true values are n2 = 4.140±0.02 and k2 = 0.034±0.01 for 5461 Å.
K. VEDAM, W. KNAUSENBERGER, and F. LUKES, "Ellipsometric Method for the Determination of All the Optical Parameters of the System of an Isotropic Nonabsorbing Film on an Isotropic Absorbing Substrate. Optical Constants of Silicon," J. Opt. Soc. Am. 59, 64-71 (1969)