Imaging oxygen defects and their motion at a manganite surface.

Manganites are technologically important materials, used widely as solid oxide fuel cell cathodes; they have also been shown to exhibit electroresistance. Oxygen bulk diffusion and surface exchange processes are critical for catalytic action, and numerous studies of manganites have linked electroresistance to electrochemical oxygen migration. Direct imaging of individual oxygen defects is needed to underpin understanding of these important processes. Currently, it is not possible to collect the required images in bulk, but scanning tunnelling microscopy (STM) could provide such data for surfaces. Here, we report the first atomic resolution images of oxygen defects at a manganite surface. Our experiments also reveal defect dynamics, including oxygen adatom migration, vacancy-adatom recombination and adatom bistability. Beyond providing an experimental basis for testing models describing the microscopics of oxygen migration at transition-metal oxide interfaces, our work resolves the long-standing puzzle of why STM is more challenging for layered manganites than for cuprates.