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First Results From Aberration Corrected Z-Contrast Imagine1

A. R. Lupini2, S. J. Pennycook3

Full Article (PDF 528 KB)

The Scanning Transmission Electron Microscope (STEM) is one of the foremost tools in many areas of materials science. In particular, the Z-contrast mode available in such a microscope offers considerable advantages over the conventional electron microscope. These images, obtained on a high-angle annular dark field detector (HAADF), are directly interpretable images of the atomic column positions and are free of the contrast reversal that plagues conventional bright field images. A further advantage of the Z-contrast mode is that it can be combined with electron energy loss spectroscopy (EELS), which provides information on composition and electronic structure at atomic resolution. The main factor that limits the resolution of such an instrument is the spherical aberration (Cs) of the objective lens. This aberration is unavoidable in conventional electron lenses, and so in order to improve the performance of the instrument, the lens aberrations must be corrected. Towards this end, we have recently installed an aberration corrector in our 100 kV Vacuum Generators HB501 STEM3. As shown in Figure 1, the aberration corrector has already provided an increase in the attainable resolution from 2.2 Å to better than 1.4 Å, which is presently the highest resolution yet achieved at 100 kV accelerating voltage, comparable to the resolution of our 300 kV microscope. Work is underway on both the microscope stabilities and on the controlling software, which is expected to provide further improvement3. The implementation of aberration correction in STEM has already provided a dramatic increase in the instrumental resolution. Imminent improvements should increase both the speed and ease of use of the system, with the goal of providing sub-Ångstrom resolution on a regular basis. The aberration corrected STEM will provide an unparalleled tool for the investigation of the structure and electronic state of a variety of materials, providing single atom sensitivity and spectroscopy.

   
 
  1. Summary of papers to be published.
  2. ORNL/ORISE post-doctoral research associate.
  3. In collaboration with O. L. Krivanek, N. Dellby and P.D. Nellist of Nion Co., Seattle.

 Oak Ridge National Laboratory