Use of Sliding-Window Fourier Transform in the Analysis of X-Ray Reflectivity Data

摘要

X-ray reflectometry allows to determine the thickness, the density and the rugosity of thin layers on a substrate from several Angstroms to some hundred nanometers. The thickness is determined by simulation with trial-and-error methods after extracting start values of the layer thicknesses from the result of a classical FFT of the reflectivity data. Nevertheless, the order information of the layers is lost during classical FFT. The order of the layers has then to be known a prori. In this paper, it will be shown that the order of the layers can be obtained by a sliding-window Fourier transform, the so-called Gabor representation. This joint time-frequency analysis allows directly to determine the order of the layers and so, to use a more appropriate starting model for refining simulation. A simulated and a measured example show the interest of this method.