Multiple scattering calculations of FeK EXAFS for Fe surfaces and nanocrystals

The curved-wave multiple-scattering theory and program FEFF were used for calculations of extended X-ray absorption fine structure (EXAFS) at the Fe K edge for the Fe (100) surface. The shape of EXAFS calculated for each atomic layer placed beneath an Fe surface down to the depth of 0.8 nm was different from the EXAFS of bulk Fe, while the EXAFS fur deeper layers was identical to that of bulk. The surface EXAFS contribution was obtained as an averaged EXAFS value for atomic layers within a depth of 0.8 nm. Three models of atomic ordering at the surfaces were taken into account: (i) an ideal surface, (ii) rough surface and (iii) statically disordered surface. It was obtained that the first peak of Fourier transform (FT) at radius R = 2.3 A is less by only 6% in the case of surface EXAFS contribution from an ideal Fe surface in comparison to that for bulk Fe, while in the case of a rough surface it is less by 24%, respectively, to bulk Fe. The FT peak at radius R = 4.5 Angstrom, which is strongly related to multiple scattering effects is even more reduced, namely by 15 and 30% for an ideal and rough surface, respectively. The Fe K EXAFS spectra were also calculated for an Fe nanocrystal in the form of a cube of size ranging from 3 to 10 nm. The theoretical model calculations were used for interpretation of the Fe K EXAFS experimental data for the nanocrystalline Fe85Zr7B6Cu2 alloy measured using synchrotron radiation. (C) 1999 Elsevier Science S.A. All rights reserved.