Preparation and characterization of Langmuir-Blodgett-type arachidate films

Metal arachidate Langmuir-Blodgett (LB) films with Pb(2+) and Cd(2+) cations and varying numbers of monomolecular layers (2 and 4 monolayers, ML) were deposited on trimethylsilylated glass substrates. The arachidate salt formation was commenced during the film deposition from a water-based solution. The extent of salt formation and the build-up of the LB layer were evaluated by quantitative XPS. The completeness of the salt formation was assessed by the atomic ratio of the carboxylic (-COO-)-type carbon component with C 1s binding energy at similar to288.5 eV to that of the selected line of the actual cation. The surface coverage of the glass substrate by the LB film was assessed by calculations based on a substrate-overlayer model using the XPS MultiQuant program. According to this model, the attenuation of the Si 2p photoelectron signal from the substrate by the 2 and 4 ML LB films (with 56 and 112 A thickness, respectively) was calculated and compared with the measured intensities, enabling the completeness of the layer to be evaluated. The layer thickness values calculated from the measured intensity of the layer constituents reflected accurately the thickness derived from the geometry of the arachidate molecule, confirming both the adequacy of the model and the accuracy of the measurement. In agreement with earlier results it was confirmed that salt-based LB films are fairly stable under high vacuum conditions, although slow decomposition of lead arachidate films was detected during prolonged x-ray irradiation. Copyright (C) 2002 John Wiley Sons, Ltd.