Ellipsometry in Interface Science

This chapter presents the basics of ellipsometry and discusses some recent advances made in the field. It covers the formalism and theory used for data analysis as well as instrumentation. The treatment is also designed to familiarize newcomers to this field. The experimental focus is on adsorption layers at the air-water and oil-water interface. Selected examples are discussed to illustrate the potential as well as the limits of this technique. The aim of the chapter is to present the wider use of this technique in the colloidal physics and chemistry community. Ellipsometry refers to a class of optical experiments, which measure changes in the state of polarization upon reflection or transmission on the sample of interest. It is a powerful technique for the characterization of thin films and surfaces. In favorable cases, thicknesses of thin films can be measured to within A accuracy. Moreover, it is possible to quantify submonolayer surface coverages with a resolution down to 1/100 of a monolayer or to measure the orientation adopted by the molecules on mesoscopic length scales. The high sensitivity is remarkable if one considers that the wavelength of the probing light is on the order of 500 nm. The data accumulation is fast and allows to monitor the kinetics of adsorption processes. The technique can also be extended to a microscopy. Imaging ellipsometry allows under certain conditions a direct visualization of surface inhomogeneities as well as quantification of the images. Many samples are suitable for ellipsometry and the only requirement is that they must reflect laser light. Its simplicity and power makes ellipsometry an ideal surface analytical tool for many objects in interface science.