## Capillary wave fluctuations and intrinsic widths of coupled fluid-fluid interfaces: An x-ray scattering study of a wetting film on bulk liquid

An x-ray specular reflectivity (XR) and off-specular diffuse scattering (XDS) study of the coupled thermal capillary fluctuations and the intrinsic profiles of two interacting fluid-fluid interfaces is presented. The measurements are carried out on complete wetting films of perfluoromethylcyclohexane (PFMC) on the surface of bulk liquid eicosane (C20), as a function of film thickness 30<D<160 A. In order to facilitate the analysis and interpretation of the data with minimal complexity, approximate methods for calculating scattering intensities are developed to take into account the subtleties of thermal diffuse scattering from layered liquid surfaces. With these methods, the calculations of XR/XDS intensitiesmore »