Peter Bolgert
Mentor: Yijin Liu
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What is porosity
What do you mean by pixel?
What is the 15 micron in the figure?
Do you know what your paper will show? E.g. An analysis of some sample
TXM XANES and X-Ray Tomography on Beamline 6-2: Data Analysis and Visualization
This summer I will be working at the SSRL with my mentor Yijin Liu. Specifically, I
will be analyzing two and three dimensional data taken via transmission X-ray microscopy
(TXM) at Beamline 6-2C. This microscope is capable of operating at energies from ~5 to 14
keV, with spatial resolution as high as 30 nm.
Although this beamline has just finished a user run, there is a considerable amount of data
to analyze. By imaging a sample using a variety of TXM techniques, we can determine the
elemental map (the exact spatial distribution of each element present in the sample), chemical
map (the exact location of each chemical phase, e.g. the location of NiO vs. Ni metal), density,
porosity, and much more.
Users and beamline scientists at 6-2 have been implementing XANES (X-ray absorption
near edge structure) spectroscopy when doing TXM imaging in order to get chemical distribution
at 30 nm resolution. Basically, every chemical species has a unique XANES spectrum (a graph
of the absorption coefficient vs. x-ray photon energy). Obviously there will be a big jump at the
K-edge of the element (the energy required to ionize an inner shell electron). For different
chemical species of the same element (e.g. NiO vs. Ni metal), the edge on the absorption plot
will be at the same energy (with a small edge shift), but with slightly different shapes. By
analyzing the subtle features of the absorption curve, you can determine the various chemical
species which are present.
The figure below summarizes the process. First the sample is imaged at a range of
energies, making sure to include the K-edge of interest. Then, for each pixel you have obtained a
XANES spectrum. By comparing your data with the XANES spectra of known chemical
species, you can determine the exact chemical distribution of the sample.
For my project, I will be performing the analysis depicted below. There are many steps
needed to prepare the images, such as reference correction, magnification correction, alignment,
etc. To perform these procedures, we use the Matlab program “TXM-Wizard,” written by Yijin
Liu, Florian Meirer, and Phillip Williams. In addition to performing XANES analysis, I will be
using the program Aviso Fire to create high quality visualizations. My group is fairly new to the
Aviso Fire software, and hopefully I can help the group use software more creatively and
effectively.
Figure 1 : Adapted from Florian Meirer et al., “3D imaging of chemical phase transformations,” J. Synchrotron Rad. (2011).