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Atomic-Resolution Z-Contrast Imaging of Crystals

SJ Pennycook1

Nature 336, 565 (1989)

Full Article (PDF 432 KB)

Figure 1 shows direct images of the atomic scale chemistry of two high Tc superconductors YBa2Cu3O7-x (Y123) and ErBa2Cu3O7-x (ER123) obtained with a new electron microscopy technique. The superconducting (curremt carrying) planes are seen as dark vertical lines in both materials, and each individual layer in the structures can be resolved and unambiguously identified. The technique uses a very fine electron probe of diameter 2-3 angstroms which is scanned across a thin sample of the material. Most of the beam passes right through — hence, the instrument is called a scanning transmission electron microscope. This new image is obtained by measuring the intensity scattered through angles of typically 1° to 3° and recording this as the probe is scanned across the sample in the form of a TV raster. The physics of the scattering is such that heavy elements appear brightest. Therefore, we achieve chemical sensitivity through the scattering process combined with the atomic resolution of the fine electron probe. The calculated intensity profiles shown below each material correlate closely with the experimental images, and demonstrate the chemical sensitivity when the heavy rare-earth Er is substituted for Y.

This technique is the first fundamentally new method for imaging the atomic structure of bulk materials in 40 years (as distinct form the imaging of surfaces in the scanning tunneling microscope). It is expected to have a major impact in understanding how the superconducting planes are broken by imperfections n real material, and how to avoid it.

 

 

 
Figure 1.
 
 
  1. Solid State Division, Oak Ridge National Laboratory

 Oak Ridge National Laboratory