Effect of specimen misalignment on local structure analysis using annular dark-field imaging.

We have investigated the effects of a small misalignment of the crystallographic orientation with respect to an incident probe (i.e. crystal tilt) on annular dark-field (ADF) imaging in scanning transmission electron microscopy (STEM). In STEM-ADF imaging with a small convergence angle, crystal tilt causes an artifact such as a shift of the bright spots corresponding to atomic columns. The displacement of the spots in ADF images differs for each atomic column, resulting in the breakdown of the incoherent imaging approximation. For a large convergence angle, in contrast, bright spot positions correctly correspond to the atomic positions. A multislice simulation indicates that the superior intuitive interpretability for a large convergence angle is due to a small depth of focus. The findings suggest that a large convergence angle enables the accurate measurement of atomic positions as well as improved spatial resolution.