Mass Transport in Oxide Thin Films - Visualization and Control

Device miniaturization has long stimulated great interest in the development of thin films and means for the characterization of their properties.  This trend has more recently been directed towards solid state ionic devices, stimulated by the growing interest in micro-batteries, -fuel cells and –sensors.  Mass transport is likewise believed to control the operation of one of the latest memory technologies based on the so-called memristive effect. 

Whether in bulk or thin film form, a fundamental understanding of oxygen defect equilibria and transport kinetics is essential for achieving enhanced performance and longevity in many oxide-based device applications. The ability to diagnose a material’s behavior under operating conditions in situ, is therefore of importance.  Achieving this in thin films is often more challenging given their low mass and support-film interactions.  Here we present experimental results obtained by a novel experimental technique developed in our laboratory capable of simultaneously performing in situ optical absorption and electrochemical impedance spectroscopy (EIS) measurements over a wide range of temperatures and controlled atmospheres.  We show, when applied to model materials systems such as Pr_xCe_1-xO_2-δ (PCO), that these techniques are capable of deriving a detailed picture of the defect equilibria and transport properties of such materials and determining whether and to what degree they differ from bulk properties. We also show how monitoring time and spatially dependent changes in optical absorption can be used to study oxygen exchange and diffusion kinetics and discuss the impact of surface chemistry and metal current collector on the reaction kinetics. Finally, we report on recent color front migration studies in PCO films designed to extract oxygen diffusivities.