Ellipsometry techniques

Several techniques have been developed to measure the electro-optic susceptibility of single crystals or thin films. All are based on the measurement of variation of the refractive index of a material induced by the applied external field. We will shortly describe the modulation ellipsometry technique [18,19], which is relatively simple in use and can be applied to thin films, provided that some precautions are undertaken [20]. 

Fig.1. Schematic representation of multilayer structure and experimental set-up efficient measurements by the modulation ellipsometry technique...

The properties of adsorbed layers at liquid interfaces can be determined either indirectly by thermodynamic methods or directly by means of some particular experimental techniques, such as radiotracer and ellipsometry. For adsorbed layers of synthetic polymers or biopolymers the advantages of the ellipsometry technique become evident as it yields information not only on the adsorbed amount but also on the thickness and refractive index of the layer. The theoretical background of ellipsometry with regard to layers between two bulk phases has been described in literature quite frequently (243). In brief, the principle of the method assumes that the state of polarization of a light beam is characterized by the amplitude ratio Ep E and the phase difference (8 — 8g) of the two components of the electric-field vector E. These two components Ep and E are parallel (p) and normal (s) to the plane of incidence of the beam and given by... 

The optical constant such as refractive index, and the thickness of a film are determined by ellipsometry. For polymer thin films the reflection ellipsometry technique is commonly used. This technique is especially useful in the wavelength regions where the materials are strongly absorbing so that the transmission measurements are precluded. 

Monolayers of PDA were prepared by spreading a solution of PDA in petroleum ether or hexane on a thoroughly cleaned water surface (pH = 2)in a glass trough with paraffin coated edges. The surface density of molecules was controlled by a movable Teflon barrier and the surface tension was measured by a Wilhelmy plate. For the ellipsometry measurements we used a weak He-Ne laser at 632.8 nm. The phase shift was measured by a standard high resolution ellipsometry technique.5 The accuracy in (j> was 10 4 rad. 

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