Ex situ and in situ characterization of surfactant monolayers adsorbed on nonmetallic substrate by infrared reflection spectroscopy

Abstract

AbstractThe adsorbed (self‐assembled) submonolayers and monolayers structure, orientation and chemical interaction at the interface of nonmetallic (semiconductor) have been studied by infrared reflection spectroscopy. The experimental data collected from in situ and ex situ measurements have led us to propose mechanisms of interaction between surfactants and surfaces. 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 major problem is the interpretation of the recorded reflection spectra which are modified by optical effects, compared with the corresponding transmission spectra of the same layer on a transparent support. The developed method makes it possible to interpret the experimental reflection spectra on the basis of spectral simulation data. It is shown that it is possible to obtain reliable chemical and structural information on the adsorption layer and distinguish it from other observed spectral modifications due to optical effects. The high sensitivity of this method permits the investigation of ultrathin layers (submonolayers). By combination of the simulated and experimental data, the orientation angles of the transition moments of the major infrared bands and the thickness of the adsorption layers were evaluated.