I visited the Advanced Photon Source (APS) at the Argonne National Lab (USA) from March 4 to March 17, 2017.  My main goal for this stay was to learn how to use synchrotron x-ray diffraction techniques in combination with externally heated diamond anvil cells (DAC).  The DAC is a high pressure device in which the sample is compressed between two diamond anvils. Due to the very high hardness of diamond, it is possible to build up a pressure of several hundreds of GPa with a DAC.
During my stay at the APS, I was supervised by Dr. C. Prescher. He taught me how to prepare DACs. In detail, I learned how to align and glue the diamonds and to prepare gaskets for different diamond culet sizes. This is only the first step for DAC preparation. The most challenging part for this kind of experiments is to load the sample in the DAC, due to the very small sample chamber size (usually below 250 µm). Therefore, every step has to be monitored under microscope, so this work needs a lot of patience since sample loading can take anything from a couple of minutes to a full day.
Beside the DAC preparation, I picked up a lot of theoretical background and concepts of x-ray diffraction, including the application of x-ray optics such as a soller slit to gain a higher resolution of the diffraction pattern.
I was also trained to run experiments at a beamline on my own. This procedure includes the insert of the DAC, the alignment of the beam and the measurements. Furthermore, I learned how to use the data processing software Dioptas to analyze the diffraction pattern.
During the two weeks, I met scientists from the Lawrence Livermore National Laboratory (LLNL), the Geophysical Laboratory (Washington DC) and the German Research Centre for Geosciences (GFZ Potsdam). The discussions we had were very stimulating and highly interesting. I got new insights into my research field.  

For me this was a great enrichment of my academic training. I was able to improve my skills in dealing with DAC experiments and I learned how to perform experiments at synchrotron facilities. Furthermore, I gained insight into the kind of heavy workload of operating the synchrotron day and night.

Johannes Stefanski   
PhD Student

Institute of Geology and Mineralogy

PhD Project “Properties and Structure of Fluids in Geological Processes”