Wissenschaftliche Artikel der BAM
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- 2016 (2) (entfernen)
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- Englisch (2)
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- Synchrotron radiation (2) (entfernen)
Grating interferometric set-ups have been established in the last decade. They are promising candidates to obtain enhanced image contrast from weakly absorbing micro and nano structures. They are based on X-ray refraction and near-field diffraction using the Talbot effect.
At the expense of taking multiple images, Talbot-Lau grating interferometry allows separating the absorption, refraction, and scattering contributions by analysing the disturbances of a phase grating interference pattern. Contrary to other refraction enhanced methods, this technique can be applied using conventional X-ray tubes (divergent, polychromatic source). This makes it attractive to solve typical non-destructive testing problems.
We investigated the efficiency of phase gratings, i.e. the visibility (the amplitude of oscillations) upon variation of propagation distance and phase grating rotation around an axis parallel to the grid lines. This grating rotation changes the grating shape (i.e. the distributions of phase shifts). This can yield higher visibilities than derived from rectangular shapes.
Our study includes experimental results obtained from synchrotron radiation, as well as simulations for monochromatic radiation. The advantages of Talbot-Lau interferometry are demonstrated at the example of glass capillaries.
A combined analysis of EXAFS and Raman spectra is applied for the study of
InxGa1-xN alloys with 0.3<x<0.5. Alloying causes relaxation of the selection rules resulting in
Raman spectra that resemble the vibrational density of states. On the other hand, theoretical
simulation of the Raman spectra using the Equation of Motion routine of FEFF8 provides the
vibrational component of the Debye-Waller factor (DWF). The static disorder component of
the DWFs was obtained by fitting the Ga and In K-edge EXAFS spectra. The analysis revealed
that the nearest neighbor distances of the 1st and 2nd shell deviate from the values predicted by
the law of Vegard and the virtual crystal approximation. The static disorder in the first nearest
neighboring shell (In-N and Ga-N) is null whereas in the cation-cation neighboring shells the
static component is generally smaller than the vibrational.