Synchrotron-Based X-Ray Absorption Spectroscopy of Iron Silicon Germanide and Osmium Silicide Grown by Molecular Beam Epitaxy*

Some of the iron- and osmium-based metal silicide and germanide phases have been predicted to be direct band gap semiconductors. Therefore, they show promise for use as optoelectronic materials. We have used synchrotron-based x-ray absorption spectroscopy to study the structure of iron silicon germanide and osmium silicide films grown by molecular beam epitaxy. Osmium silicide films which are primarily in the Os$_{2}$Si$_{3}$ phase and a series of Fe(Si$_{1-x}$Ge$_{x})_{2}$ films with a nominal Ge concentration of up to x = 0.04 have been grown. X-ray absorption near edge structure (XANES) measurements on both the iron silicon germanide and osmium silicide films has been performed. An absorption edge shift of 0.9 eV is observed for the osmium silicide films; however, no shift was observed for the iron silicon germinide films. Extended x-ray absorption fine structure (EXAFS) measurements have also been performed on the iron silicon germanide films. The nearest neighbor co-ordination corresponding to the $\beta $-FeSi$_{2}$ phase of iron silicide provides the best fit with the EXAFS data.