Oxygen vacancies facilitate or govern the interfacial phenomenon observed at or across well-defined discrete interfaces, ranging from mixed ionic electronic conduction to memristive systems. Realization of multifunctionality within oxide heterostructures necessitates a direct understanding of the interrelationship exhibited by concomitant, defect-mediated transport mechanisms with adequate spatial resolution. Examples include utilizing in situ scanning probes the surface potential is measured across a four-layer yttria-stabilized zirconia / strontium titanate (YSZ/STO) film at 500 °C, and electroactive Au/GDC electrode interfaces under co-electrolysis environments. Semiconductor dopant analysis reveals the effects of vacancy distributions and migration on potential evolution, and confirms oxygen exchange between the films and substrate, which result in a micron-scale depletion region into the bulk. The second example explores recent studies of ligand effects on the resistive switching within solution processed nanoparticle assemblies. Here we show improvements to both operating parameters such as set/reset voltage and overall uniformity. We also introduce 3D conductive AFM nanotomography to directly observe the morphological evolution of conductive filaments comprising oxygen vacancies. These results demonstrate promise in resolving defect-mediated functionality in oxide heterostructures, under extreme environmental perturbation, on a highly localized scale.
Stephen S. Nonnenmann is an Associate Professor in Mechanical & Industrial Engineering at the University of Massachusetts-Amherst. He received a B.S. in Glass Engineering Science at Alfred University, then a M.S. in Materials Science & Engineering and the University of Central Florida. Nonnenmann then earned a Ph.D. in Materials Science and Engineering from Drexel University, and then served as a postdoctoral research at Princeton University and as a Nano Bio Interface Center postdoctoral fellow at the University of Pennsylvania. Since Prof. Nonnenmann joined UMass in 2013, he has been recognized with a NSF CAREER Award, the College of Engineering Outstanding Teacher Award, and the COE Outstanding Junior Faculty Award. His research focuses on identifying interfacial transport mechanisms, electromechanical coupling, and electrochemical phenomena within oxide materials using in situ local probes within dynamic environments.