SPHERICAL WAVE EXAFS ANALYSIS OF THE SILICON K-EDGE X-RAY ABSORPTION-SPECTRUM

The silicon K-edge EXAFS spectrum was analyzed by spherical wave formalism. The agreement between the exptl. EXAFS spectrum at >50 eV beyond the K-threshold and the theor. one was obtained using exptl. values of the mean free path and of the different Debye-Waller factors for each shell. Seven shells around the absorbing atom were considered in the calcn., but the amplitude due to the distant shells decreased rapidly with the distance, and at >80 eV only the contribution of the 1st 3 shells is important. The single scattering contribution .chi.2(k) using the spherical wave approach can explain the exptl. .chi.(k) = (.mu.(k) - .mu.0(k))/.mu.0(k) spectrum only >50 eV. At lower energies there are strong multiple scattering effects and it is necessary to take account of other terms .chi.n(k) (with n >2) of the expansion .chi.(k) = nv2.chi.n(k).