Michael, On Sun, Nov 20, 2016 at 5:41 AM, Karl-Michael Schindler < karl-michael.schindler@physik.uni-halle.de> wrote:
Hi.
I would appreciate hints about how to treat multiple domains in Athena. The simplest system would be one with only twofold rotational symmetry, but present in two domains rotated by 90°. Somehow equivalent to the case of unpolarized x-rays.
I am fairly new to using Athena and i may have simply missed the answer in the documentation.
Michael.
X-ray absorption averages over the atoms in the volume illuminated by the beam. As the beam is attenuated by the sample, fewer X-rays make it to portions of that volume at depth. If you have multiple local structures in your sample, the XAFS signal is a simple average of those local structures, weighted by the probability that an atom with a particular structure absorbs an X-ray. For a uniform sample with a mixture of sites, that weighting is the simply the fraction of atoms with each structure. If the sample is not uniform, it can be more complicated. In particular, heterogeneity that is a function of depth (say, a layered material) is more complicated, because atoms near the surface are more likely to absorb the X-ray than samples at depth. Hope that helps, --Matt