Ion transport in thin oxide Films

Ion motion is one of the most fundamental kinetic processes in ionic solids and the basis of many chemical and physical phenomena such as solid state reactions, sintering, compositional variations, and ionic current. Ion transport is also made use of in a number of high-tech applications of functional ceramics such as chemical sensors, fuel cells, batteries and oxygen pumps. Moreover, it plays an important role in degradation of dielectric and piezoelectric devices. However, the knowledge on ion motion in thin oxide films of a few 10 to 100 nm thickness is still very limited. The number of investigations dealing with this topic has increased recently but the results of many studies are still only partly understood or even contradictory and often suffer from misinterpretations. This is in strong contrast to the expanding importance of thin oxide films in several novel and emerging technologies using functional (smart) materials such as ferroelectric memories (FeRAMS), miniaturized sensors and electronic noses, pyroelectric detector arrays, micro fuel cells, high-k dielectrics in microelectronics, piezoelectrics for micro-electro-mechanical systems (MEMS), etc. In view of these applications as well as from a fundamental point of view, an improved understanding of ion transport in thin oxide films is highly desirable and a need for further reliable experimental data and proper interpretation is obvious. It is the prime goal of this project to employ complementary tools available in two research groups for achieving a substantial step forward in understanding mass and charge transport as well as defect chemistry in thin oxide films. Layers of two model materials prepared by pulsed laser deposition will be in the focus of research: yttria stabilized zirconia (as a model solid electrolyte) and SrTiO3 (as a model mixed conductor with low room temperature conductivity). Electrical measurements (including microcontact impedance spectroscopy) will be performed to investigate the role of bulk, interfaces, and grain boundaries on lateral as well as perpendicular mass and charge transport in zirconia and SrTiO3 thin films. In an extensive complementary study, secondary ion mass spectrometry (SIMS) of field-driven tracer profiles will be employed to further analyze ion transport in these films and to visualize the effects of possibly enhanced or decreased interfacial conduction in lateral and perpendicular ion transport. The combined investigation of in-plane and perpendicular conduction processes in both a purely ionic and a mixed conducting model system using two complementary experimental tools (impedance spectroscopy and SIMS) will hopefully lead to a firm knowledge base on which future studies on other thin oxide films can rely on. Moreover, these basic investigations can yield valuable information for a better understanding of ion transport related to processes taking place in novel devices employing thin oxide layers as functional elements.

Ion motion is one of the most fundamental kinetic processes in ionic solids and the basis of many chemical and physical phenomena such as solid state reactions, sintering, compositional variations, and ionic current. Ion transport is also made use of in a number of high-tech applications of functional ceramics such as chemical sensors, fuel cells, batteries and oxygen pumps. Moreover, it plays an important role in degradation of dielectric and piezoelectric devices. However, the knowledge on ion motion in thin oxide films of a few 10 to 100 nm thickness is still very limited. The number of investigations dealing with this topic has increased recently but the results of many studies are still only partly understood or even contradictory and often suffer from misinterpretations. This is in strong contrast to the expanding importance of thin oxide films in several novel and emerging technologies using functional (smart) materials such as ferroelectric memories (FeRAMS), miniaturized sensors and electronic noses, pyroelectric detector arrays, micro fuel cells, high-k dielectrics in microelectronics, piezoelectrics for micro-electro-mechanical systems (MEMS), etc. In view of these applications as well as from a fundamental point of view, an improved understanding of ion transport in thin oxide films is highly desirable and a need for further reliable experimental data and proper interpretation is obvious. It is the prime goal of this project to employ complementary tools available in two research groups for achieving a substantial step forward in understanding mass and charge transport as well as defect chemistry in thin oxide films. Layers of two model materials prepared by pulsed laser deposition will be in the focus of research: yttria stabilized zirconia (as a model solid electrolyte) and SrTiO3 (as a model mixed conductor with low room temperature conductivity). Electrical measurements (including microcontact impedance spectroscopy) will be performed to investigate the role of bulk, interfaces, and grain boundaries on lateral as well as perpendicular mass and charge transport in zirconia and SrTiO3 thin films. In an extensive complementary study, secondary ion mass spectrometry (SIMS) of field-driven tracer profiles will be employed to further analyze ion transport in these films and to visualize the effects of possibly enhanced or decreased interfacial conduction in lateral and perpendicular ion transport. The combined investigation of in-plane and perpendicular conduction processes in both a purely ionic and a mixed conducting model system using two complementary experimental tools (impedance spectroscopy and SIMS) will hopefully lead to a firm knowledge base on which future studies on other thin oxide films can rely on. Moreover, these basic investigations can yield valuable information for a better understanding of ion transport related to processes taking place in novel devices employing thin oxide layers as functional elements.