Correlating imaging and spectroscopy at atomic resolution in the STEM

The study of materials by electron microscopy has traditionally been divided into two sub-fields, imaging and microanalysis. While both of these have advanced to the level of atomic sensitivity, a complete characterization of a materials structure, composition and bonding requires a correlation between the two. This correlation has been achieved through the combination of Z-contrast imaging and electron energy loss spectrocopy (EELS) in the scanning transmission electron microscope (STEM). For the highly coherent and convergent probe in the STEM, the scattering to a high-angle detector (40- 150 mrad) shows an intensity which is proportional to the Z2-dependence of the Rutherford scattering cross-section. The resultant "Z-contrast" image, which is generated point-by-point as the probe is scanned over the surface of the specimen, can be described as a simple convolution of the probe intensity profile, P2eff (R), and a specimen object function O(R,t), This incoherent description of image intensity holds for crystalline materials in zone-axis orientations where dynamical diffraction manifests itself as a columnar channeling effect.