An “on-line” correction method of defocus and astigmatism in HAADF-STEM

The imaging characteristics of high-angle annular detector dark field scanning transmission electron microscopy (HAADF-STEM) and the Fourier transform patterns of the images are formulated under the projected potential approximation. By using the Fourier transform patterns, it is clarified from the present theoretical and experimental studies that the defocus and astigmatism of objective lens in STEM are corrected “on-line”, which is very useful for finally tuning HAADF-STEM in high-resolution observation.