Atomic scale structure and chemistry of interfaces by Z-contrast imaging and electron energy loss spectroscopy in the STEM

The macroscopic properties of many materials are controlled by the structure and chemistry at grain boundaries. A basic understanding of the structure-property relationship requires a technique which probes both composition and chemical bonding on an atomic scale. High-resolution Z-contrast imaging in the scanning transmission electron microscope (STEM) forms an incoherent image in which changes in atomic structure and composition across an interface can be interpreted directly without the need for preconceived atomic structure models (1). Since the Z-contrast image is formed by electrons scattered through high angles, parallel detection electron energy loss spectroscopy (PEELS) can be used simultaneously to provide complementary chemical information on an atomic scale. The fine structure in the PEEL spectra can be used to investigate the local electronic structure and the nature of the bonding across the interface (3). In this paper we use the complimentary techniques of high resolution Z-contrast imaging and PEELS to investigate the atomic structure and chemistry of a 25° symmetric tilt boundary in a bicrystal of the electroceramic SrTiO₃.