Herstellung und Charakterisierung von duennen Schichten im Hinblick auf die Monochromatisierung von Synchrotronstrahlung mit Hilfe des Moessbauereffekts

SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Phonon density of states in Fe/Cr (001) superlattices and Tb-Fe thin-film alloys.

Inelastic nuclear scattering of X-rays from the 14.413 keV nuclear resonance of {sup 57}Fe was employed to measure directly the Fe-projected phonon density of states (DOS) in MBE-grown Fe/Cr(00l) superlattices on MgO(001). The Moessbauer-inactive {sup 56}Fe isotope was used in the Fe layers. A 1{angstrom} thick Moessbauer-active {sup 57}Fe-probe layer (95% enriched) was placed at different locations within the Fe layers. This procedure permits one to distinguish phonon density of states at the Fe-Cr-interface from that at the center of the Fe-film. Distinct differences have been observed in the DOS of our samples. The phonon DOS of an amorphous Tb{sub 33}Fe{sub 67} alloy film was found to be a broad and structureless hump, contrary to that of an epitaxial TbFe{sub 2} film, which exhibits characteristic features

Disentangling magnetic order on nanostructured surfaces

We present a synchrotron-based x-ray scattering technique which allows disentangling magnetic propertiesof heterogeneous systems with nanopatterned surfaces. This technique combines the nanometer-range spatialresolution of surface morphology features provided by grazing incidence small angle x-ray scattering and thehigh sensitivity of nuclear resonant scattering to magnetic order. A single experiment thus allows attributingmagnetic properties to structural features of the sample; chemical and structural properties may be correlatedanalogously. We demonstrate how this technique shows the correlation between structural growth and evolutionof magnetic properties for the case of a remarkable magnetization reversal in a structurally and magneticallynanopatterned sample system

Spectral narrowing of x-ray pulses for precision spectroscopy with nuclear resonances

Spectroscopy of nuclear resonances offers a wide range of applications due to the remarkable energy resolution afforded by their narrow linewidths. However, progress toward higher resolution is inhibited at modern x-ray sources because they deliver only a tiny fraction of the photons on resonance, with the remainder contributing to an off-resonant background. We devised an experimental setup that uses the fast mechanical motion of a resonant target to manipulate the spectrum of a given x-ray pulse and to redistribute off-resonant spectral intensity onto the resonance. As a consequence, the resonant pulse brilliance is increased while the off-resonant background is reduced. Because our method is compatible with existing and upcoming pulsed x-ray sources, we anticipate that this approach will find applications that require ultranarrow x-ray resonances

Towards meV resolution above 40 keV with sapphire X-ray ultraoptics

Recent developments of the sapphire backscattering monochromator enabled an energy resolution of ΔE/E~10-8 in the 21-40keV energy range. Nuclear inelastic scattering, NIS, studies of the lattice dynamics on Eu, Sm, Sn, Te, Sb and Xe compounds are thus possible with meV to sub-meV resolution at the ID18 ESRF beam line.Although theoretical calculations show the possibility to use sapphire backscattering monochromator above 40keV with resolution ΔE/E~10-8 or better, an experimental realization has not yet been achieved.meV-monochromatization above 40keV is required in order to perform nuclear resonance scattering experiments on 183-W at 46.5keV, 238-U at 44.9keV, 232-Th at 49.4keV, 157-Gd at 54.5keV, 239-Pu at 57.3keV, 127-I at 57.6keV, 159-Tb at 58.0keV, 237-Np at 59.5keV and to measure element specific density of phonon states in related compounds