An auto-tuning method for focusing and astigmatism correction in HAADF-STEM, based on the image contrast transfer function

An auto-tuning method for high-angle annular detector dark field scanning transmission electron microscopy (HAADF-STEM) is proposed which corrects the defocus to the optimum Scherzer focus and compensates the astigmatism: Because the method is based on the image contrast transfer function formulated for the HAABF-STEM, the defocus and the astigmatism an accurately measured from input of two different defocus images. The method is designed to work independent of object function in the Linear ig model by analysing the spectral ratio between two Fourier spectra of their images, which is useful for cases where the spectrum of object function is not uniformly spread our over the reciprocal space. The method was preliminarily tested in a Hitachi HD-2000 STEM, and successful results of the auto-tunings from the viewpoint of verification of the algorithm were obtained using general specimens of Au fine particles and a thin section of a semiconductor device.