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

TL;DR

This study investigates how specimen mistilt affects picometer-scale measurements in ABF-STEM imaging, proposing a method to distinguish tilt effects from noise and distortion for more accurate atomic structure analysis.

Contribution

A relative distance measurement method is introduced to separate tilt effects from scan noise and distortion in ABF-STEM imaging.

Findings

Small specimen tilt causes significant artificial atomic displacements.

Tilt effects can dominate over scan noise and distortion.

Insights into detecting and correcting tilt effects for accurate structure analysis.

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 scan 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 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.