ABSTRACT
Understanding and tuning epitaxial complex oxide films are crucial in controlling the behavior of devices and catalytic processes. Substrate-induced strain, doping, and layer growth are known to influence the electronic and magnetic properties of the bulk of the film. In this study, we demonstrate a clear distinction between the bulk and surface of thin films of La0.67Sr0.33MnO3 in terms of chemical composition, electronic disorder, and surface morphology. We use a combined experimental approach of X-ray-based characterization methods and scanning probe microscopy. Using X-ray diffraction and resonant X-ray reflectivity, we uncover surface nonstoichiometry in the strontium and lanthanum alongside an accumulation of oxygen vacancies. With scanning tunneling microscopy, we observed an electronic phase separation (EPS) on the surface related to this nonstoichiometry. The EPS is likely driving the temperature-dependent resistivity transition and is a cause of proposed mixed-phase ferromagnetic and paramagnetic states near room temperature in these thin films.
ABSTRACT
Mass production of green hydrogen via water electrolysis requires advancements in the performance of electrocatalysts, especially for the oxygen evolution reaction. In this feature article, we highlight how epitaxial nickelates act as model systems to identify atomic-level composition-structure-property-activity relationships, capture dynamic changes under operating conditions, and reveal reaction and failure mechanisms. These insights guide advanced electrocatalyst design with tailored functionality and superior performance. We conclude with an outlook for future developments via operando characterization and multilayer electrocatalyst design.
ABSTRACT
Polymer brushes, coatings of polymers covalently end-grafted to a surface, have been proposed as a more stable alternative to traditional physisorbed coatings. However, when such coatings are applied in settings such as vapor sensing and gas separation technologies, their responsiveness to solvent vapors becomes an important consideration. It can be anticipated that the end-anchoring in polymer brushes reduces the translational entropy of the polymers and instead introduces an entropic penalty against stretching when vapor is absorbed. Therefore, swelling can be expected to be diminished in brushes compared to nongrafted films. Here, we study the effect of the anchoring-constraint on vapor sorption in polymer coatings using coarse-grained molecular dynamics simulations as well as humidity-controlled ellipsometry on chemically identical polymer brushes and nongrafted films. We find a qualitative agreement between simulations and experiments, with both indicating that brushes certainly swell less than physisorbed films, although this effect is minor for common grafting densities. Our results imply that polymer brushes indeed hold great potential for the intended applications.
