Complex Oxides: Structure/Properties Relations at the Atomic Scale Maria Varela Condensed Matter Sciences Division Oak Ridge National Laboratory In the nanoscience era, the properties of many exciting new materials and devices will depend on the details of their composition down to the level of single atoms. Thus the characterization of the structure and electronic properties of matter at the atomic scale is becoming ever more vital for economic and technological as well for as scientific reasons. The combination of atomic-resolution Z-contrast scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) represents a powerful method to link the atomic and electronic structure to macroscopic properties, allowing materials, nanoscale systems, and interfaces to be probed in unprecedented detail. Recent developments in aberration correction have pushed the achievable spatial resolution and the sensitivity for imaging and spectroscopy in the STEM into the sub-angstrom regime, providing a new level of insight into the structure/property relations of complex materials. This level of sensitivity allows us to analyze in great detail the crystal and electronic structures of complex oxides at the atomic scale. Images now show greatly improved contrast and signal to noise ratio, sufficient to allow sensitivity to light atoms (such as oxygen columns) and even to single atoms in both imaging and spectroscopy. This work will present several examples of atomic resolution studies of the relationship between structure and electronic properties of complex oxide thin films and interfaces, with complementary density-functional calculations. Materials examples will include charge ordering and phase separation in colossal magnetoresistant manganites, interface charge transfer across high Tc superconducting interfaces and the study of dilute magnetic semiconductor thin films.