Spherical Waves Exafs and Multiple-scattering Effects In Xanes of the K-edge Spectrum of Silicon

The siliconK-edgeEXAFS (extended X-rayabsorption fine structure) spectrum has been analyzed by sphericalwave formalism. The agreement between the experimental EXAFSspectrum in the energy range above 50 eV beyond the K-threshold and the theoretical one has been obtained using experimental values of the mean free path and of the different Debye-Waller factors for each shell. Seven shells around the absorbing atom have been considered in the calculation, but the amplitude due to the distant shells decreases rapidly with the distance, and above 80 eV only the contribution of the first three shells is important. We show that the single scattering contribution Ξ2 (k) using the sphericalwave approach can explain the experimental Ξ(k) = (μ(k) − μ0(k))/μ0(k) spectrum only above 50 eV. At lower energies there are strong multiple scattering effects and it is necessary to take account of other terms Ξn(k) (with n > 2) of the expansion Ξ(k) = Σn=2∞Ξn(k).