3-fold astigmatism is not always corrected in a TEM. Its effect on HREM images can be simulated by introducing its amplitude and direction in the HREM map panel of the Bloch-wave calculation and the HREM map panel and super-cell imager in the multislice calculations.
It has the effect to shift the interference fringes. It has always to be considered when HREM images of interfaces are acquired for it is orientation dependent and the deformation of the interface motif can be severe. Furthermore a artificial rigid body shift is introduced by three-fold astigmatism.
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Figure 1 Au Σ5310 no 3-fold astigmatism (atomic columns). |
Figure 2 Au Σ5310 3-fold astigmatism (atomic columns). |
Figure 3 Au Σ5310 no 3-fold astigmatism. |
Procedures for correcting axial coma and three fold astigmatism have been described in:
K. Ishizuka, Coma-free alignment of a high resolution electron microscope with three-fold astigmatism, Ultramicroscopy 55 (1994) 407-418.
O.L. Krivanek, Three-fold astigmatism in high-resolution transmission electron microscopy, Ultramicroscopy 55 (1994) 419-433.
K. L. Merkle, R. Csencsits, K. L. Rynes, J. P. Withrow, P. A. Stadelmann, The effect of three-fold astigmatism on measurements of grain boundary volume expansion by high-resolution transmission electron microscopy, J. Microscopy 190 (1998) 204-213.