Optical Characterization of Organic Thin Films and Interfaces with Evanescent Waves

Abstract

Among the numerous experimental techniques available for comprehensive materials characterization, light optical methods play an outstanding role. Based, in all cases, on the interaction of electromagnetic radiation with matter in various configurations (e.g., for absorption, thermalization, re-emission, elastic and inelastic scattering, or for microscopic imaging experiments), optical techniques provide detailed information about many structural, electronic, and other materials properties. Typically, propagating electromagnetic waves (“normal” photons) are used for these studies, and a broad spectrum of powerful optical instruments is available for investigating all kinds of bulk materials. However, where thinner and thinner samples are of interest—eventually only one monomolecular layer (or even less) thick—some of these standard techniques lack the sensitivity necessary to be useful. On the other hand, there is a growing (nano)tech-nological demand for thin-film preparations especially in the polymeric materials area, e.g., as thin lubricating, isolation, or protective coatings, for integrated or nonlinear optical devices, or to increase the biocompatibility of inorganic materials. This has stimulated the development of novel optical techniques with increased sensitivity, specificity, and spatial resolution. For interfacial properties and thin film samples, the use of a different kind of light, called evanescent waves, has proved in recent years to be particularly helpful because their high surface specificity allows sensitive monitoring of the properties of interfaces and thin layers without the interference of information from the bulk.