SPHERICAL-ABERRATION-FREE OBSERVATION OF TEM IMAGES BY DEFOCUS-MODULATION IMAGE-PROCESSING

Defocus-modulation image processing has been applied to correct the spherical aberration in transmission electron microscopic images. The correction procedure is performed by off-line integration of through-focus images with bipolar weighting functions. An electron microscope with a field emission gun, the HF-2000, was used in this experiment. The Thon diagrams constructed by plotting the power spectra of the processed images as a function of virtual defocus value clearly demonstrate that the spherical aberration was corrected very well, leading to the marked improvement of the resolution from 3.7 to 5.8 nm-1. As a novel approach to assess the information limit more accurately, we have represented the Thon diagrams for the amplitude and phase components separately. The presented results reveal that this approach is of practical use even for thicker samples which cannot be treated as weak phase objects.