Cerium reduction at the interface between ceria and yttria-stabilised zirconia and implications for interfacial oxygen non-stoichiometry

Epitaxial CeO2 films with different thickness were grown on Y2O3 stabilised Zirconia substrates. Reduction of cerium ions at the interface between CeO2 films and yttria stabilised zirconia substrates is demonstrated using aberration-corrected scanning transmission electron microscopy combined with electron energy-loss spectroscopy. It is revealed that most of the Ce ions were reduced from Ce 4+ to Ce3+ at the interface region with a decay of several nanometers. Several possibilities of charge compensations are discussed. Irrespective of the details, such local non-stoichiometries are crucial not only for understanding charge transport in such hetero-structures but also for understanding ceria catalytic properties

Inhomogeneous ferromagnetism mimics signatures of the topological Hall effect in SrRuO3 films

Topological transport phenomena in magnetic materials are a major topic of current condensed matter research. One of the most widely studied phenomena is the topological Hall effect (THE), which is generated via spin-orbit interactions between conduction electrons and topological spin textures such as skyrmions. We report a comprehensive set of Hall effect and magnetization measurements on epitaxial films of the prototypical ferromagnetic metal SrRuO3 the magnetic and transport properties of which were systematically modulated by varying the concentration of Ru vacancies. We observe Hall effect anomalies that closely resemble signatures of the THE, but a quantitative analysis demonstrates that they result from inhomogeneities in the ferromagnetic magnetization caused by a nonrandom distribution of Ru vacancies. As such inhomogeneities are difficult to avoid and are rarely characterized independently, our results call into question the identification of topological spin textures in numerous prior transport studies of quantum materials, heterostructures, and devices. Firm conclusions regarding the presence of such textures must meet stringent conditions such as probes that couple directly to the noncollinear magnetization on the atomic scale

Optoelectronic Inactivity of Dislocations in Cu In,Ga Se2 Thin Films

High efficiency Cu In,Ga Se2 CIGS thin film solar cells are based on poly crystalline CIGS absorber layers, which contain grain boundaries, stacking faults, and dislocations. While planar defects in CIGS layers have been investigated extensively, little is still known about the impact of dislocations on optoelectronic properties of CIGS absorbers. Herein, evidence for an optoelectronic inactivity of dislocations in these thin films is given, in contrast to the situation at grain boundaries. This unique behavior is explained by the extensive elemental redis tribution detected around dislocation cores, which is connected with the dislocation strain field, probably leading to a shift of defect states toward the band edge

Recent TEM developments applied to quantum structures

To shed light on these confined properties, a technique with a high energy-and-spatial resolution is of absolute need. Modern transmission electron microscopy (TEM) is the most suitable technique for a direct measurement of optical and structural properties at a nanometer scale. Thanks to the successful construction of aberration corrected transmission electron microscopes, the mapping of atomic positions with high accuracy becomes a routine experiment enabling therefore a more intuitive interpretation of structural deformation (strain). In addition, the recent development in energy-filters, especially when coupled to monochromated electron-beams, measurements of physical properties are achieved with unprecedented performances. The case of individual buried GaN/(AlGaN) quantum dots is discussed

Recent TEM developments applied to quantum structures

To shed light on these confined properties, a technique with a high energy-and-spatial resolution is of absolute need. Modern transmission electron microscopy (TEM) is the most suitable technique for a direct measurement of optical and structural properties at a nanometer scale. Thanks to the successful construction of aberration corrected transmission electron microscopes, the mapping of atomic positions with high accuracy becomes a routine experiment enabling therefore a more intuitive interpretation of structural deformation (strain). In addition, the recent development in energy-filters, especially when coupled to monochromated electron-beams, measurements of physical properties are achieved with unprecedented performances. The case of individual buried GaN/(AlGaN) quantum dots is discussed