Simplified analysis of some complex film stacks in x-ray reflectivity

X-ray reflectivity (XRR) is commonly used to measure the thickness, density, and roughness of thin films. XRR can be used on multilayered films, however the data analysis then involves a complex fit. Such fits display many local minima for stacks of more than two layers. It is shown how the modulated diffuse scattering arising from the correlated roughness effect can sometimes be used to measure the thickness of the top film in the stack, hence reducing the size of the parameter space to be searched. Data for three- and four-layer stacks will be presented.