THE SURFACE SENSITIVITY OF FLUORESCENCE EXAFS AT REFLECTION CONDITIONS

Abstract
The development of reflection EXAFS methods has led to the technique becoming a potentially important tool for the study of solid surfaces. Here we present the results for thin films of silver supported on quartz substrates. Two experimental measurements can be used to collect reflection EXAFS data, i.e. detection of 1) the emitted fluorescence or 2) the reflected X-ray beam. Both detection methods have been employed in this work and, of the two, the latter method has been shown to be more surface sensitive. Fluorescence is less so because of contributions from deeply penetrating X-rays which are not involved in the reflection process. These effects can be understood by considering the dynamical theory of X-ray scattering which is consistent with our experimental data. The results from Ag films indicate that, under atmospheric conditions, the metal surface is covered with a thin layer of oxide. Additional data suggests that the surface coating is 2 monolayers of oxide, the reflection EXAFS data suggests that this coating has a structure similar to AgO.