MULTIPLE-SCATTERING EFFECTS IN THE K-EDGE X-RAY-ABSORPTION NEAR-EDGE STRUCTURE OF CRYSTALLINE AND AMORPHOUS-SILICON

The exptl. extn. is reported of the multiple-scattering contribution to the K-edge XANES of cryst. Si. The multiple-scattering signal, was obtained by taking the difference .chi.expt(k)-.chi.2(k) = .chi.MS(k) = n=3 .chi.n(k) where .chi.expt(k) is defined as [.alpha.(k) - .alpha.0 (k)]/.alpha.0(k), .chi.2 is the spherical-wave-calcd. extended EXAFS signal, and the .chi.n's are the multiple-scattering contributions to the total absorption coeff. .alpha.(k) assumed to have the form .alpha.(k) = .alpha.0(k))[1 + n=2.chi.n(k)] over the full wave-vector range, .alpha.0(k) being the at. absorption coeff. The .chi.2 term was calcd. over the full energy range by using a spherical-wave formula and including mean-free-path and Debye-Waller effects. By using the subtraction procedure, a .chi.MS oscillation of large amplitude was found in the 1st 70 eV of the spectrum. Comparison with the theor. double scattering .chi.3(k) gives account of the main features of the .chi.MS(k) spectrum. The main .chi.3 contribution comes from the double scattering paths involving atoms of the 1st as well as of the 2nd shell, and higher terms of the series (n > 3) are damped by the finite core hole lifetime and the inelastic losses of the photoelectron in the final state.