Comparison of glancing angle extended x-ray absorption fine structure obtained from fluorescence and reflectivity measurements

Abstract

At glancing angles the extended x-ray absorption fine structure (EXAFS) can be determined from either the fluorescence or reflectivity signals. This article presents a critical comparison of the two detection channels as they apply to thin film interface problems. Both signals are distorted by anomalous dispersion effects, and our previous method for correcting the distortions in the fluorescence signal is shown to work equally well for the reflectivity signal. Using results from a pure gold film and a Cu-Al bilayer as examples, it is demonstrated that both signals can be corrected to obtain accurate EXAFS information. Fluorescence detection generally offers greater sensitivity, improved signal-to-noise and less distortion of the EXAFS, but the reflectivity signal may be easier to obtain for in situ measurements. A complication for fluorescence is the possibility of an additional contribution to the signal caused by x rays scattered into the substrate layer. While generally small, this contribution is difficult to remove from the measured signal, and may make the reflectivity the preferred signal for some experiments.