Iron K-edge absorption spectroscopic investigations of the cores of ferritin and haemosiderins.

The extended X-ray absorption fine structure (EXAFS) associated with the iron K-edge has been measured and interpreted for ferritin and haemosiderin extracted from horse spleen, and haemosiderin extracted from the livers of humans with treated primary haemochromatosis, and from the spleens of humans with treated secondary haemochromatosis. For ferritin, the data are consistent with, on average, each iron atom being in an environment comprised of approx. six oxygen atoms at 1.93 +/- 0.02 A, approx. 1.5 iron atoms at 2.95 +/- 0.02 A and approx. 1.1 iron atoms at 3.39 +/- 0.02 A, with a further shell of oxygens at approx. 3.6 A. Iron in horse spleen haemosiderin is in an essentially identical local environment to that in horse spleen ferritin. In contrast, the EXAFS data for primary haemochromatosis haemosiderin indicate that the iron-oxide core is amorphous; only a single shell of approx. six oxygen atoms at approx. 1.94 +/- 0.02 A being apparent. Secondary haemochromatosis haemosiderin shows an ordered structure with approx. 1.4 iron atoms at both 2.97 +/- 0.02 and 3.34 +/- 0.02 A. This arrangement of iron atoms is similar to that in horse spleen haemosiderin, but the first oxygen shell is split with approx. 2.9 atoms at 1.90 +/- 0.02 A and approx. 2.7 at 2.03 +/- 0.02 A, indicative of substantial structural differences between secondary haemochromatosis haemosiderin and horse spleen haemosiderin.

Structure of nickel layers in ni-C multilayer coatings: influence of annealing.

The structure of Ni-C multilayer and single nickel layer samples has been analyzed before and after annealing, using two techniques: fluorescence EXAFS (F1EXAFS) at the Ni-K. edge and CuKα reflection. Annealing at a temperature of 450°C resulted in a change in the structure of the nickel layers from amorphous like to crystalline like. A reduction of the Bragg reflectivity by a factor of 7 was also found. Comparison between the EXAFS data of the annealed sample and of a nickel foil show a difference in the amplitude of the EXAFS. This is ascribed to a non-Gaussian atomic distribution of the backscattering atoms in the annealed sample around their average positions, whereas the atomic distribution in the (polycrystalline) Ni foil is a Gaussian one. From the annealing experiments we conclude that no irreversible changes take place in the structure of the nickel layers at temperatures below 200°C.