Final Report Summary - STEMOX (Under the light of electrons)
The STEMOX project started with the aim of exploring emerging phenomena in low dimensional and artificially structured oxide based systems by means of advanced electron microscopy and spectroscopy techniques. Complex oxides are intriguing materials, which exhibit very unique properties including collective phenomena such as magnetism, ferroelectricity or superconductivity, amongst others. Low dimensional systems based on complex oxides, such as superlattices of nanostructured materials, may exhibit new behaviors that do not exist in bulk, such as metallicity in two-dimensional electron gases. Such physical properties may change drastically due to minor chemical or structural variations. Often, it is only via real space techniques that can look at matter in an atom-by-atom fashion that we can harness these novel states. In this context, the STEMOX team set off to explore the physics of oxides in low dimensional environments, with a special emphasis on studying phenomena related to interfacial magnetism. Interfaces control the behavior of many nanoscale systems including the emergence of novel functionalities, some of which are not present in any of the constituent materials. We have been able to synthetize and characterize high quality oxide based heterostructures and nanometric magnetic materials of interest in electronics, spintronics or energy, and then we have developed new imaging techniques in order to explore the Physics of such systems. We have used atomic resolution spectroscopy in the electron microscope to simultaneously map their electronic and magnetic properties by means of novel techniques sensitive to magnetic quantities, pushing the limits of magnetic imaging at high spatial resolution in the electron microscope. The team was the first one ever to report atomic resolution maps of spin states in solids, mapping the spin state of Co atoms in nanometer-sized pockets of cobaltite thin films. We saw unexpected spin state superlattices associated with O vacancy ordering. Being able to obtain this information on a local scale can resolve many of the mysteries of magnetic nanostructures, since the magnetic properties of materials are not solely determined by the local ordering of magnetic moments, but also their actual values. This finding established the feasibility for atomic resolution magnetic mapping using near edge fine structure features. Also, new imaging techniques combining spectrum imaging with electron magnetic circular dichroism (EMCD) were developed to generate EMCD spectrum imaging (EMCDSI) maps that would help studying magnetization at the local level. For the first time, the electron microscope was used to map the magnetization of nanoparticles in real space with sub-nanometer spatial resolution, along with their structure, chemistry and electronic properties. Being able to obtain this information on a local scale will resolve many of the mysteries of magnetic nanostructures and thin films. The STEMOX team has applied these techniques to the study of electronic and magnetic properties of a number of low dimensional systems (nanoparticles, nanowires, interfaces, etc) of technological relevance. In parallel, a solid group devoted to study materials physics by means of advanced microscopy techniques has been established in Madrid in close collaboration with growth and theory, also contributing to the set up of a microscopy laboratory with two aberration corrected electron microscopes at the Host Institution.