3 results
Search Results
Now showing 1 - 3 of 3
- ItemComparative study of sculptured metallic thin films deposited by oblique angle deposition at different temperatures(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2018) Liedtke, Susann; Grüner, Christoph; Gerlach, Jürgen W.; Rauschenbach, BerndMetals with a wide range of melting points are deposited by electron beam evaporation under oblique deposition geometry on thermally oxidized Si substrates. During deposition the sample holder is cooled down to 77 K. It is observed that all obliquely deposited metals grow as tilted, high aspect ratio columns and hence with a similar morphology. A comparison of such columns with those deposited at room temperature (300 K) reveals that shadowing dominates the growth process for columns deposited at 77 K, while the impact of surface diffusion is significantly increased at elevated substrate temperatures. Furthermore, it is discussed how the incidence angle of the incoming particle flux and the substrate temperature affect the columnar tilt angles and the porosity of the sculptured thin films. Exemplarily for tilted Al columns deposited at 77 K and at 300 K, in-plane pole figure measurements are carried out. A tendency to form a biaxial texture as well as a change in the crystalline structure depending on the substrate temperature is found for those films.
- ItemRole of Reaction Intermediate Diffusion on the Performance of Platinum Electrodes in Solid Acid Fuel Cells(Basel : MDPI, 2021) Lorenz, Oliver; Kühne, Alexander; Rudolph, Martin; Diyatmika, Wahyu; Prager, Andrea; Gerlach, Jürgen W.; Griebel, Jan; Winkler, Sara; Lotnyk, Andriy; Anders, André; Abel, BerndUnderstanding the reaction pathways for the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) is the key to design electrodes for solid acid fuel cells (SAFCs). In general, electrochemical reactions of a fuel cell are considered to occur at the triple-phase boundary where an electrocatalyst, electrolyte and gas phase are in contact. In this concept, diffusion processes of reaction intermediates from the catalyst to the electrolyte remain unconsidered. Here, we unravel the reaction pathways for open-structured Pt electrodes with various electrode thicknesses from 15 to 240 nm. These electrodes are characterized by a triple-phase boundary length and a thickness-depending double-phase boundary area. We reveal that the double-phase boundary is the active catalytic interface for the HOR. For Pt layers ≤ 60 nm, the HOR rate is rate-limited by the processes at the gas/catalyst and/or the catalyst/electrolyte interface while the hydrogen surface diffusion step is fast. For thicker layers (>60 nm), the diffusion of reaction intermediates on the surface of Pt be-comes the limiting process. For the ORR, the predominant reaction pathway is via the triple-phase boundary. The double-phase boundary contributes additionally with a diffusion length of a few nanometers. Based on our results, we propose that the molecular reaction mechanism at the electrode interfaces based upon the triple-phase boundary concept may need to be extended to an effective area near the triple-phase boundary length to include all catalytically relevant diffusion processes of the reaction intermediates. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
- ItemOberflächenchemie nano- und mikrodimensionaler Materialien und Werkstoffe : Schlussbericht zum Vorhaben ; Laufzeit: 01.09.2008 bis 31.01.2012(Hannover : Technische Informationsbibliothek (TIB), 2012) Rauschenbach, Bernd; Gerlach, Jürgen W.; Hirsch, Dietmar; Mändl, Stephan; Arnold, Th.; Mießler, André; Prager, Lutz; Prager, Andrea; Elsner, Christian; Reichelt, Senta; Pender, Alya[no abstract available]