Employing an aberration corrector in a high-resolution transmission electron microscope, the spherical aberration CS can be tuned to negative values, resulting in a novel imaging technique, which is called the negative CS imaging (NCSI) technique. The image contrast obtained with the NCSI technique is compared quantitatively with the image contrast formed with the traditional positive CS imaging (PCSI) technique. For the case of thin objects negative CS images are superior to positive CS images concerning the magnitude of the obtained contrast, which is due to constructive rather than destructive superposition of fundamental contrast contributions.
from FZJ

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FZJ on NCSI