The use of transmission EXAFS for concentrated systems is well established. In some cases, when the systems under investigation become increasingly dilute in the absorbing atom there is a point where the signal to noise (S/N) ratio favors alternative techniques which measure signals characteristic of the absorbing species (X-Ray fluorescence and Auger electron detection, for example). Auger emission and fluorescence are competing processes. Their relative strengths depend on the atomic number of the absorber. In light elements Auger emission is more probable, while for heavy elements fluorescence becomes more likely.
When energy discrimination is required, as for our samples, a fluorescence detector, single photon counting is necessary. Only the solid state and gas scintillation proportional detectors have resolutions sufficient for separating a fluorescence line from the background. The real need for energy resolution in the detector is to isolate interfering fluorescence lines from a multicomponent sample.
Samples for our studies were grown by molecular beam epitaxy of Ge and Si layers utilizing the Stranski-Krastanov growth mode on Si (001) substrates. We would like to present some EXAFS spectroscopy results for Ge single layers (with different thickness) buried in Si matrix at different temperatures of Ge layer deposition (about 210-250 and 700-750oC).
These measurements were done with using of X-Ray fluorescence 7 element Si detector at the A1 station (HASYLAB), which is equipped with high energy resolution monochromator. To reduce a temperature disorder we prefer to perform the measurements at LN temperatures.
Using these techniques we observed the changes in atomic order around the Ge, and respectively Si, atoms in investigated samples depending on the growth conditions and both the Ge and Si layer thickness and compared the formed atomic order with that in crystalline Ge and Si, and solid solution with different concentrations of Ge (x=0.1-0.9).