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Cu measurements

The sample was a 25 mm diameter 2000Å thick Cu(111) film grown epitaxially by vapor deposition onto freshly cleaved mica. The c-axis mosaic spread of the film was about tex2html_wrap_inline1762 FWHM, making it relatively easy to track the Bragg peak versus energy. A thin sample was chosen to minimize the effects of sample x-ray absorption. The diffracted intensities at 8500 eV, about 500 eV below the edge, were tex2html_wrap_inline1768 photons per second for the Cu(111) Bragg reflection and tex2html_wrap_inline1770 photons per second for the Cu(222) reflection. Relative to the incident intensity, the diffracted intensities were tex2html_wrap_inline1772 and tex2html_wrap_inline1774 for these two Bragg reflections, and the diffracted intensities were well described by the kinematic approximation.

The measured intensities versus energy for the Cu(111) and Cu(222) Bragg reflections are shown in Fig. 5a together with the corresponding fluorescence XAFS signal for comparison. The cusp in the Bragg intensity drops at the edge energy, tex2html_wrap_inline1776 eV, to about tex2html_wrap_inline1778 of the pre-edge intensity at 8500 eV for the Cu(111) reflection and to about tex2html_wrap_inline1782 for the Cu(222) reflection. This difference in the relative cusp drop between the two reflections is caused by the decrease in tex2html_wrap_inline1398 with tex2html_wrap_inline1434. The fine structure oscillations above the absorption edge are present in both the DAFS and XAFS signals and have similar sizes, tex2html_wrap_inline1788 peak-to-peak, when normalized to their corresponding cusp drop or edge step sizes.