Direct oxygen imaging within a ceramic interface, with some observations upon the dark contrast at the grain boundary

Annular bright field scanning transmission electron microscopy, which has recently been established to produce directly interpretable images with both light and heavier atomic columns visible simultaneously, is shown to allow directly interpretable imaging of the oxygen columns within the Σ 13 [ 1 2 ¯ 1 0 ] ( 1 0 1 ¯ 4 ) pyramidal twin grain boundary in α -Al 2 O 3 . By using information in the high-angle annular dark field image and annular bright field images simultaneously, we estimate the specimen thickness and finite source size, and use them to explore in simulation the issue of dark contrast in the vicinity of the grain boundary in the annular dark field image.