Synchrotron
BESSY II Synchrotron – BERLIN
At the Helmholtz Zentrum in Berlin, I work at the BESSY II synchrotron. This impressive building, shaped like a ring, hide a very impressive and powerful research tool.
Learn more here!
What is a Synchrotron?
A synchrotron is a type of particle accelerator that uses a combination of electric and magnetic fields to accelerate electrons to very high speeds. The electrons are then directed into a circular path (storage ring) giving the annular shape of the building. They can reach speeds close to the speed of light, and the resulting high-energy beams can be used to produce X-rays. For that, the electrons go through so called ondulators, composed of strong magnets, moving the electrons around, accelerating them and thus producing the X-ray photons. This is called Bremsstrahlung emission. These X-rays are then used for spectroscopy such as X-ray absorption, Photoemission, etc.
Where can I find a Synchrotron?
In Europe, there are 10 main synchrotrons in 8 different countries. Each of them have they specificities. For instance, DESY synchrotron, with the PETRA III storage ring, is one of the most brilliant storage ring based X-ray source worldwide. The accelerator produces a particle energy of 6 GeV and three experimental halls host up to 30 experiments simultaneously. Because of the large energy of the electrons accelerated, DESY is also one of the largest synchrotron with circumference of more than 2 km!
On the contrary, BESSY II, in Berlin, where I work, opened in 1998, is 1.7 GeV for a circumference of 240 m. However, in contrary to other synchrotrons, BESSY produces low energy X-ray, called soft X-ray, perfect to study carbon materials and diamonds!
The biggest is not always the best.
What do I do with BESSY II?
In BESSY II synchrotron, I characterize diamond materials such as single crystals, diamond wafers and nanodiamonds using X-ray. I perform X-ray absorption spectroscopy (XAS), which enables to determine the surface chemistry of the diamonds with great precision, and X-ray photoemission spectroscopy (XPS), that enables to quantify the different atoms and chemical bonds on the diamonds.
The great advantage of using a synchrotron for XPS, in contrary to lab based XPS, is that the resolution in energy is much better and that changing the excitation energy, I can probe the sample more or less deep. And believe me, it helps to understand the measurement!
I also develop in situ XAS in order to measure the diamonds in contact with water. This is extremely important to understand what happens at the interface between the diamond and the liquid, and develop new materials for (photo)electrochemistry. However, it is challenging because the X-ray we use only travel through vacuum and are easily absorbed by any materials. Did you ever try to put water under vacuum?
To measure at the synchrotron, we apply for a beamtime. If granted, we have one week, days, and nights to perform our experiments. It's quite an adventure! And it is a team work. We take shifts with colleagues to rest a bit, and we can count on the great support of the beamline scientists, working on the measurement station.