10. Applications of Aberration-Corrected Scanning Transmission Electron Microscopy and Electron Energy Loss Spectroscopy to Complex Oxide Materials

The success of aberration correction in the scanning transmission electron microscope (STEM) is revolutionizing the study of complex oxide materials, especially transition metal oxides. These are fascinating systems that exhibit the most disparate physical behaviors such as colossal magnetoresistance, orbital and/or charge ordering, magnetoelectronic phase separation or high Tc superconductivity to just name a few. Thanks to their relatively large lattice parameters and the fact that both O and transition metals exhibit absorption edges well within the reach of modern electron energy loss spectrometer (EELS) optics, they are ideal systems for such types of electron microscopy studies. Since many of the aforementioned phenomena exhibit characteristic length scales in the nanometer regime, they are affected by reduced dimensionality (e.g., thin films or heterostructures), proximity to other materials, or depend on nanometric active regions (e.g., defects, interfaces, etc.). Understanding such phenomena must therefore rely heavily on probes capable of studying simultaneously the structure, chemistry and electronic properties with atomic resolution in real space. In this chapter we will review a number of applications of aberration corrected STEM-EELS to transition metal oxides, mainly those with the perovskite structure. We will go over the current state-of-the-art of the techniques, capabilities, sensitivity and interpretation of measurements and apply this knowledge to the study of bulk and nanoscale systems, thin films and interfaces based on materials such as cuprates, titanates, manganites and cobaltites.