Multiple-scattering effects in the K-edge x-ray-absorption near-edge structure of crystalline and amorphous silicon.

摘要: We report the experimental extraction of multiple-scattering contribution to K-edge x-ray-absorption near-edge structure spectrum (XANES) crystalline silicon. The signal, is obtained by taking difference ${\mathrm{\ensuremath{\chi}}}_{\mathrm{expt}}$(k)-${\mathrm{\ensuremath{\chi}}}_{2}$(k)=${\mathrm{\ensuremath{\chi}}}_{\mathrm{MS}}$(k)= where ${\ensuremath{\chi}}_{\mathrm{expt}(\mathrm{k})}$ defined as [\ensuremath{\alpha}(k)-${\ensuremath{\alpha}}_{0}$(k)]/${\ensuremath{\alpha}}_{0}$(k), ${\ensuremath{\chi}}_{2}$ spherical-wave-calculated extended fine-structure (EXAFS) and ${\ensuremath{\chi}}_{n}$'s are contributions total absorption coefficient \ensuremath{\alpha}(k) assumed have form \ensuremath{\alpha}(k)=${\mathrm{\ensuremath{\alpha}}}_{0}$(k)[1+ over full wave-vector range, ${\ensuremath{\alpha}}_{0}$(k) being atomic coefficient. term has been calculated energy range using a spherical-wave formula including mean-free-path Debye-Waller effects. By subtraction procedure we find ${\ensuremath{\chi}}_{\mathrm{MS}}$ oscillation large amplitude in first 70 eV spectrum. Comparison with theoretical double scattering ${\ensuremath{\chi}}_{3}$(k) gives account main features ${\ensuremath{\chi}}_{\mathrm{MS}(\mathrm{k})}$ show that ${\ensuremath{\chi}}_{3}$ comes from paths involving atoms well second shell higher terms series (ng3) damped finite core hole lifetime inelastic losses photoelectron final state. Finally analyze spectra amorphous contrary case, suppressed. Its suppression assigned orientational disorder bond angles phase.