X-ray scattering and atomic force microscopy study of melting of Langmuir-Blodgett films

Abstract

Melting of 9-ML cadmium arachidate Langmuir-Blodgett (LB) films, having logarithmic and self-affine interfacial height-height correlations, has been studied by x-ray specular reflectivity, diffuse scattering, and atomic force microscopy (AFM). Although analysis of AFM images and diffuse scattering data for both films indicates that the respective in-plane correlation of the untreated films remains unchanged up to $100\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ it is evident from analysis of the diffuse integrated reflectivity data that a reduction of electron density at metal sites occurs as a function of temperature. Between 100 and $110\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ the film disorders completely and the bilayer structure breaks down. A systematic analysis of x-ray and AFM data suggest that a disordering prior to the melting of LB films takes place predominantly via lateral motion of molecules, keeping the interfacial correlation unchanged irrespective of the interfacial morphology of the untreated film.