Composition and structure of self-assembled layers at molecular level

Abstract

The structure, orientation and chemical interaction of self-assembled submonolayers and monolayers at the interface of non-metallic (semiconductor, dielectric) and metallic substrates were studied by IR reflection spectroscopy. The reflection spectra of the adsorbed layers on different substrates recorded at different angles of incidence and for two polarizations are an excellent source of information about the composition and structure of the layers. The reflection spectra of the surface layer can be recorded for any type of substrate: transparent, opaque or non-transparent. The major problem is the interpretation of the recorded spectra which are modified by optical effects, compared with the corresponding transmission spectra of the same layer without a substrate support. The method developed allows one to interpret the experimental reflection spectra on the basis of spectral simulation data. This work demonstrates that it is possible to obtain information on chemical and structural changes in the adsorption layer and distinguish them from other observed spectral modifications due to optical effects. The high sensitivity of this method permits the investigation of ultrathin layers (submonolayers). In this presentation the experimental and calculated spectra of adsorption layers of surfactants on different types of substrate are discussed for various experimental conditions. By combination of the simulated and experimental data, the orientation angles of the transition moments resulting from major IR bands and the thickness of the adsorption layers were evaluated.