AN ELLIPSOMETRIC METHOD FOR THE CHARACTERIZATION OF MACROSCOPICALLY HETEROGENEOUS FILMS

In conventional compensating ellipsometry one usually measures a polarizer and an analyzer angle and computes from them two optical parameters of a layered structure, provided the individual layers are laterally homogeneous. In order to study a macroscopically heterogeneous thin layer with domains larger in lateral dimension than the wavelength of light, we suggest that furthermore the light intensity be measured at compensation. The additional light intensity, delta I, exceeding the value for the homogeneous layer, results from the incoherent superposition of the light reflected from the different domains. From the polarizer and analyzer angles at compensation one obtains the arithmetical average of the optical single domain properties, whereas delta I quantifies the heterogeneity, i. e. the relative areas of the domains and the differences in their optical thicknesses. In special cases this allows for the determination of the optical properties of the domains separately. The model is tested with films composed of two phases, the difference being a fatty acid bilayer of 5. 6 nm in thickness. Application of the model include the study of phase transitions in lipid monolayers.