Thickness effect on the extended-x-ray-absorption-fine-structure amplitude

The thickness effect, which is caused by inevitable leakage radiation accompanying the desired radiation, can cause significant decreases of extended-x-ray-absorption-fine-structure (EXAFS) amplitude when the sample is thick enough. The effect is illustrated by measurements of the $K$-edge EXAFS on a series of copper foils of varying thicknesses. Significant distortions in EXAFS amplitudes occur when $\Delta {\mu }_{0}x\ge 1.5$, where $\Delta {\mu }_0$ is the $K$-edge step in the absorption coefficient and $x$ is the sample thickness. Therefore, the optimum total sample thickness of ${\mu }_{T}x=2.6\mathrm{}$ as determined by statistical considerations will introduce errors in EXAFS amplitudes in concentrated samples due to the thickness effect. The measurements presented here determine the most accurate values of EXAFS amplitude for copper metal which agree well with theory as corrected for the many-body overlap effect.