Specific approach of generalized ellipsometry for the determination of weak in-plane anisotropy: application to Langmuir–Blodgett ultrathin films

Abstract

We report on a procedure of generalized ellipsometry for the determination of the optical constants of stratified samples that present a weak in-plane anisotropy. We first derive the analytical expressions of the Jones reflection matrix and of the detected intensity for a rotating-polarizer ellipsometer configuration. These expressions show that the in-plane birefringence and the orientation of the principal axes of the dielectric tensor can be obtained from a measurement of the normalized off-diagonal terms of the reflection matrix as a function of the sample azimuth, followed by a Fourier analysis and a wavelength-by-wavelength inversion of these experimental data. We apply this method to the optical characterization of Langmuir–Blodgett molecular films deposited on silicon substrates. The obtained results show that even for transparent and ultrathin films it is possible to accurately determine very weak in-plane birefringence and axis orientations.