Experimental study of annular bright field (ABF) imaging using aberration-corrected scanning transmission electron microscopy (STEM)

Experimental parameters used in the annular bright field (ABF) imaging method were tested using images simulated with the multislice method. Images simulated under identical conditions were found to agree well with experimental images. The ABF technique was shown to be relatively insensitive to the sample thickness and the defocus. In experimental ABF images, atomic columns exhibited dark contrast over a wide range of specimen thickness and defocus values, from 10 to 70 nm and −20 to +20 nm, respectively. A series of diffraction patterns at atomic columns, obtained using the diffraction imaging method, exhibited higher intensities in their central regions (0–11 mrad) for light elements and in their peripheral regions (11–22 mrad) for heavy elements. The results indicated that the contrast of light elements is enhanced by subtraction of the central region of the transmitted beam, since this is blocked by a circular mask in the ABF-STEM technique. Thus, the overall contrast of light elements is greatly improved, allowing them to be clearly visualized.