ln-Situ Characterization of Oxide Thin Films during Growth

Thin film technology is vital for several industrial sectors and it has a direct impact on many of our daily use items such as mobile phones, computers, LED lamps and many more. In this project, thin films made from a special class of materials is investigated, namely mixed ionic electronic conducting oxides. These materials are solids, consisting of different metal ions and oxygen ions and they can conduct electric current in two ways simultaneously; via electrons and via oxygen ions. These properties makes them very interesting not only for basic science, but also for several commercial applications such as sensors, fuel cells or oxygen membranes. The thin films to be investigated in the project rely in their functionality on defects, which are deviations from perfect atomic arrangement. Three types of defective structures are investigated, grains and grain boundaries, strained crystal lattices and dislocations, which are ordering faults on the atomic level. A cornerstone of the investigations is a novel technique which was recently developed in our research group at TU Wien. This technique allows to simultaneously produce thin films (with controlled variation of the three defect types discussed above) and to measure their properties with electrochemical impedance spectroscopy, an advanced measurement technique working with AC electric currents and voltages. After preparation and electrochemical analysis of the thin films, they are to be further investigated with atomic resolution. For this a special electron microscopy technique will be used, namely aberration corrected transmission electron microscopy, which allows also several further analytic techniques. Both of these project parts require very specialized equipment and experienced scientists, consequently this project will be realized at two research institutions in Austria, namely TU Wien and ESI Leoben. This project goes well beyond state-of-the-art by using (i) a novel in-situ deposition and measurement technique which is unique and gives direct insight into the thin film deposition process and (ii) by using highest resolution transmission electron microscopy techniques to correlate changes in catalytic activity or defect concentration to structural features on the atomic level.

The project "In-Situ Oxides" dealt with the investigation of so-called mixed conducting oxides (MIEC). This class of materials is important as active component in batteries or fuel cells and their further investigation is the key to novel energy (storage) technologies. We used a new investigation method called "i-PLD" at the TU Wien together with atomic resolution electron microscopy (HR-TEM) at ESI in Leoben as well as other techniques to gain a variety of new scientific insights. For example, we were able to show that several different MIEC oxides, even those with different crystal structures have the same reaction mechanism for oxygen exchange as long as their surfaces are clean. Our technique also allowed us to manipulate the surfaces at the atomic level. We were able to show that tiniest amounts (even less than a single layer of atoms, or only about 0.0000000001 grams per square centimeter) of certain surface atoms can massively improve or worsen the activity of materials. Furthermore, we found in our project that minute traces of acidic gases are often a major problem for the surface of MIEC materials. Quite similar to what was described above, smallest amounts can already make a big difference. In our scientific work, we were able to describe on the one hand how strongly the activity of surfaces is influenced, and on the other hand we were also able to clarify details about the mechanisms involved. We found out that a shift of electric charge plays a key role and that so-called double dipoles at the surface over a length of less than one nanometer (0.000000001 meter) determine whether a surface is either very active or completely unsuitable for use in a fuel cell. The interplay of three components is relevant for this: adhering gas molecules, surface atoms and the material directly underneath. In addition, we were able to present a number of other new scientific findings in 20 publications to date, in well-renowned scientific journals. They are accessible to experts and also to the general public (open access). We were also able to inspire the international scientific community for our work, our three PhD students employed through this project have won three prizes for the best presentations at conferences. Quite spectacularly, the already finished PhD thesis even received two major prizes, on the one hand from the Gemeinschaft Deutscher Chemiker as best thesis in the field of electrochemistry 2022, and on the other hand from the Austrian Academy of Sciences as best PhD thesis in Austria 2022 across all natural sciences.