In the transfer project InCamS@BI, the Innovation Campus for Sustainable Solutions of HSBI and Bielefeld University, the research group Analytics and Material Development is looking for new methods to analyze plastics. Doctoral student Judith Bünte uses electron beams to track down atoms, lattice structures and layer systems. After all, plastics can only be integrated into a circular economy if their components are known precisely.



Wearing protective goggles and gloves, Judith Bünte carefully opens an inconspicuous container and takes out a cylindrical object. It steams out of the top end. Bünte tips the smoke into a three-meter-high device: the transmission electron microscope. It's steaming liquid nitrogen, which the experimental physicist uses to keep her sample clean . She is currently still working with samples made of metal, but in the future she would like to analyze plastic samples. The 24-year-old is part of InCamS@BI, the Innovation Campus for Sustainable Solutions, a transfer project of Bielefeld University of Applied Sciences (HSBI) and Bielefeld University. In the laboratories of the university's Experimental Physics, she demonstrates the equipment she uses for this purpose.



With the electron beam through the sample

The entrance to the modern building is glazed, and the neon yellow walls can already be seen through the front. Three doors are passed, then the visitors stand in a small hallway. From here, one reaches the clean room, the scanning electron microscope (SEM) and the transmission electron microscope (TEM). Anyone expecting merely a small microscope on a table is in for a surprise: in room E0-311 there is a huge shapeless gray instrument that takes up most of the room and is connected by cables to various other elements. On a desk next to the TEM are various control units, three monitors, keyboard and mouse. Bünte knows the complicated TEM well - she already spent a lot of time here for her master's thesis.



In a transmission electron microscope, electron beams are directed at a sample and penetrate it, provided it is thin enough. The electrons are scattered by the sample and "caught" by a detector on the other side . Depending on which atoms they encounter, they behave differently. The different interactions affect such things as energy and exit angle. The interactions reveal from which areas of the sample the electrons are scattered.



In a holder, the researcher places the metal sample, which is about three millimeters in diameter. "This is a sample of the metal cobalt. A colleague made it in a so-called sputtering system because we need very thin samples for the TEM. On top of the 50 nanometer thin cobalt layer is another two nanometer layer of ruthenium to protect the sample from oxidation." Bünte slides the holder into the TEM, flips a switch. The sample is now in an airlock that prevents air from outside from entering the instrument. To prevent residual gas molecules from sticking to the sample during the study, she fills a Dewar vessel on the column of the TEM with liquid nitrogen. This serves as a refrigerant because it can maintain a temperature well below the freezing point of water - in this case, minus -196.15 degrees Celsius. The nitrogen cools a "copper cooling finger," located above the sample in the TEM, on which unwanted gases condense. This keeps the sample pure and it can now be analyzed in the TEM. A vacuum prevails in the instrument so that the air molecules do not deflect the electron beams.



Making atoms in plastics visible

"We only see tiny sections of the sample here. So small that we can look at individual atomic columns and crystal lattices," explains Bünte, who is looking at the results on the screen together with Prof. Dr. Andreas Hütten. He is her doctoral supervisor, has already supervised her first scientific work and is involved in InCamS@BI as her mentor. They are part of the InCamS@BI research group Analytics and Materials Development. The group is based at Bielefeld University and in turn consists of three working groups: AG Prof. Dr. Andreas Hütten, AG Prof. Dr. Harald Gröger and AG Prof. Dr. Dario Anselmetti. Judith Bünte is a technology scout in Andreas Hütten's group and is doing her doctorate under the expert on the physics of nanostructures, who has been researching and teaching at the university since 1997.



Back to the lab: another device used here is the FIB. The stands for Focused Ion Beam. Here, high-energy ions are used to cut a piece out of a sample and examine it with the scanning electron microscope (SEM), which is integrated into the FIB. Unlike the TEM, in the SEM an electron beam is passed over the sample in a fixed pattern. The beam does not pass through the sample, but is backscattered. Both SEM, TEM and FIB are currently used for metallic or biological samples. "What excites me most here is that I can actually see the atomic column with the microscopes," says the doctoral student. "It's a good feeling when you've adjusted the settings to the sample to get clean images. In the best case, we learn something new from the images that helps us move forward."



The next step: transferring methods for metal analysis to plastics

In the InCamS@BI project, Bünte's task is to try out these methods on plastics . "At the moment, I'm still doing a lot of literature research. I'm reading scientific publications that already exist on this subject and thinking about how we can proceed . Because depending on the type of plastic, the method would have to be adapted ," says Bünte. "The difficulty is that the atoms in plastic molecules are very light, unlike metals. So the electrons are hardly deflected and there is too little contrast on the images. So one question is: How can researchers make plastics more visible?" Another challenge: Plastics are quickly destroyed by the energy of the electron beam . Bünte and Hütten exchange ideas a lot, discuss, try new things.



Hütten has already collaborated with researchers from HSBI on various other projects and knows that interdisciplinarity pays off: "Our team is now linking up with the analytical work at the Center for Interdisciplinary Materials Research and Technology Development, or CiMT for short. There we developed toolboxes for determining the aging mechanisms of various polypropylene materials, which we can now apply to the challenges of the InCamS@BI project." Toolboxes, or more specifically a toolbox for optimizing the reuse of plastics, are what Analytics and Materials Development Research Group is now working on. The toolboxes are intended to support companies in managing circularly in the future.



A contribution to sustainability

"The more I familiarize myself with the topic of plastics on a scientific level, the more difficult it seems to me to bring this topic to society, to people outside the field, to scientific laypeople," says Bünte. Because that is also the goal of InCamS@BI: to exchange knowledge and ideas not only with industry, but also with society. And it is precisely for society that materials research in the field of plastics is enormously relevant: Hardly anyone can do without plastic products in everyday life. "There are many challenges associated with plastics - the littering of our oceans is just one of them. I find it all the more exciting that here in Bielefeld, in research, we can make our contribution to greater sustainability ."