“…The accuracy of indirect characterization methods such as ellipsometry rely on the accuracy of user-defined material parameters such as refractive index, which are often assumed or entirely unknown. X-ray reflectivity (XRR), or low-angle X-ray diffraction, provides nondestructive, accurate characterization of thin films and multilayers. ,, X-ray reflectivity probes the intensity of scattered X-rays at small angles, providing information about film thickness, roughness, and density. The fundamental framework for quantitative interpretation of X-ray reflectivity data was derived in the 1950s by Parratt, though the task of carrying out the necessary recursion calculation by hand limited its application initially to simple systems. , The advent of high-performance desktop PCs drastically reduced the requisite calculation time, allowing simulated reflectivity for complicated multilayer systems to be carried out in a matter of seconds…”