Roughness of surfaces and interfaces

X-ray reflectivity is now a common tool for investigating density profiles of thin films and multilayers in a nondestructive manner. In contrast to the specularly reflected beam the nonspecular diffuse intensity is sensitive to the lateral structure of rough interfaces. The most reliable results are obtained from simultaneous fits of all available data (i.e. reflectivity together with all diffuse scans) with a single set of parameters. It turns out that diffuse scattering experiments from a large class of systems can be described by correlation functions of self-affine fractal surfaces. Two layer systems serve as test cases: (1) A CoSi2/Si-layer system grown by molecular beam epitaxy (MBE) and (2) Langmuir-Blodgett films. The analysis within the distorted-wave Born approximation (DWBA) of the scattering from the silicide sample gives a large amount of information, e.g. strong vertical correlations. For the topmost surface a comparison between scanning tunneling microscopy (STM) and X-ray results leads to very good agreement. Nine and eleven monolayer Langmuir-Blodgett films with high defect concentrations also can be successfully analyzed with the fractal model. The lateral lengths obtained from the diffuse scattering and grazing-incidence diffraction (GID) agree.