Novel preparation methods for the fabrication of thin-film EXAFS samples

Thin-film EXAFS samples have been fabricated using semiconductor-processing and wet-chemical etching techniques to eliminate artifacts associated with transmission and fluorescence measurements. Examples include crystalline Ge _xSi_1-x alloys, amorphous GaAs and Cu and Au nanocrystals in SiO₂. In general, thin films of several microns thickness were first formed on bulk substrates then EXAFS samples were fabricated by separating the thin film and substrate. For transmission measurements, thin films were stacked together to yield the optimum absorption while sample inhomogeneity, non-uniformity and non-continuity were readily eliminated. For fluorescence measurements, scattering/diffraction from the substrate was eliminated and stacking the thin films together increased the areal concentration of the absorber. The use of such techniques to fabricate EXAFS samples yielded a significant increase in accessible photo-electron wave number range and hence more accurate structural parameter determinations.