Picometer-scale atom position analysis in annular bright-field STEM imaging

Highlights: • Specimen tilt could cause significant artifacts in ABF images. • The artifact relies on the tilt angle, thickness, defocus, convergence angle and aberrations. • The tilt induced redistribution of scattering electrons accounts for artifact. • The relative displacement measurement can effectively isolate the tilt effect. • Multislice simulation of STEM images can be used to estimate the tilt angle. - Abstract: We study the effects of specimen mistilt on the picometer-scale measurement of local structure by combing experiment and simulation in annular bright-field scanning transmission electron microscopy (ABF-STEM). A relative distance measurement method is proposed to separate the tilt effects from the scan noise and sample drift induced image distortion. We find that under a typical experimental condition a small specimen tilt (∼6 mrad) in 25 nm thick SrTiO₃ along [001] causes 11.9 pm artificial displacement between O and Sr/TiO columns in ABF image, which is more than 3 times of scan noise and sample drift induced image distortion ∼3.2 pm, suggesting the tilt effect could be dominant for the quantitative analysis of ABF images. The artifact depends on the crystal mistilt angle, specimen thickness, defocus, convergence angle and uncorrected aberration. Our study provides useful insights into detecting and correcting tilt effects during both experiment operation and data analysis to extract the real structure information and avoid mis-interpretations of atomic structure as well as the properties such as oxygen octahedral distortion/shift.