Atomic-resolution eels for composition and 3-D coordination determination at interfaces and defects

Abstract

Materials properties associated with interfaces and defects are dominated by atomic scale fluctuations in composition, structure and bonding. Although electron energy loss spectroscopy (EELS) provides a powerful tool to probe these features, low signal, lens aberrations, image coherence and specimen drift preclude the use of spectrum imaging and energy filtered imaging for these high-resolution problems. However, by utilizing Z-contrast imaging in conjunction with EELS in the scanning transmission electron microscope (STEM), these limitations are largely overcome and EELS appears capable of providing fudamental 3-D characterization of defect and interface structures with atomic resolution and sensitivity.The main premise in utilizing these combined techniques is that the properties of defects and interfaces must be associated with structural differences relative to the bulk. If those structural differences can be located, then it is only necessary to perform spectroscopy in their vicinity to understand the structure property relationship. For crystalline materials in zone-axis orientations, the Z-contrast image provides this atomic resolution structural map. As this direct image is generated with only the high-angle scattering, it can be used to position the electron probe with atomic precision and does not interfere with the low-angle scattering for spectroscopy.