Quantitative Analysis of Uniaxial Molecular Orientation in Langmuir-Blodgett Films by Infrared Reflection Spectroscopy

Abstract

In analyzing optical properties of multilayered LB films with the uniaxial anisotropy around the surface normal, a new method for calculating infrared reflection-absorbances was developed, by extending Drude's anisotropic calculation theory for two-phase system to Hansen's optical theory for thin isotropic multilayers. With this method, infrared external reflection spectra of a 9-monolayer LB film of cadmium stearate prepared on a gallium arsenide substrate were analyzed to obtain molecular orientations. The result was in fair agreement with that obtained by X-ray diffractometry. Reflection-absorbance spectra of the same LB film on a silver-evaporated slide glass at various temperatures were also analyzed by the same method and the orientation angle of each molecular group was quantitatively obtained, clarifying the process of disordering with the increase of temperature. Further, the dependence of the degree of disordering on the monolayer location in LB films were discussed in light of the isotope substitution experiment.