Thin films are nowadays utilized in many applications, ranging from semiconductor devices to optical coatings and are even present in pharmaceuticals (polymers). This wide-spread application of films with thicknesses from atomic monolayers to microns is due to the developments of thin film deposition techniques. Thin films are also important for studies of materials with new and unique properties due to the possibility of tuning their crystallographic and morphological properties. The thin film approach, i.e. the presence of interfaces (to a substrate or the film surface) adds more degrees of freedom for influencing the properties of materials, e.g. by lattice strain or surface functionalization. For these fundamental studies of material properties large research facilities such as synchrotron radiation or neutron spallation sources are one of the keys that the Paul Scherrer Institute (PSI) provides.
Our group focuses on the preparation of highly defined thin films by pulsed laser deposition (PLD) for applications in energy technology, but also for new properties, such as multiferroicity. We are working on the fundamental understanding of the PLD process, the influence of strain on material properties and we utilize the large facilities at PSI (neutrons, muons, and photons from the SLS). We therefore cooperate with many groups within the NUM, ENE and SYN divisions, and offer in addition a thin film deposition service.
Environmentally friendly energy conversion devices such as fuel cells are becoming more and more attractive. However, major impediments to large-scale application still arise on the material side, related to the cost and poor performance of the cathode catalyst. State-of-the-art electrocatalysts are all Pt-based materials, suffering from poor electrochemical oxygen reduction kinetics. Tuning the interatomic distance of Pt atoms represents a promising strategy for reducing the strength of adsorption of oxygenated species to the Pt surface and thus improving the kinetics. In this context, model Pt electrocatalysts of straininduced varied interatomic spacing were fabricated and tested. Strained Pt films
with high crystalline quality can be obtained via epitaxial growth on appropriate single-crystal substrates like (111) SrTiO3, which have lattice Parameters different from those of Pt using pulsed laser deposition. Through a proper selection of deposition parameters, the extent of strain in the Pt films can be controlled. This study shows that strain significantly modifies the electrochemical surface properties. In particular, cyclic
voltammetry and CO oxidation experiments provide valuable insights into the effect of strain on the adsorption properties of spectator species (e.g., OHad and bisulfates) relevant for oxygen reduction reaction (ORR) kinetics. Furthermore, the strained Pt films exhibit a remarkably higher oxidation reduction reaction activity compared to that of the fully relaxed bulk structure as obtained from ORR polarization curves. This research highlights the importance of proper model systems with defined physical properties to establish design principles for better-performing catalysts. Link