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

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 SrTiO 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.

Lattice relaxations around individual dopant atoms in SrTiO3

“…Sources of noise, image distortions, small residual sample tilt, and, possibly, real sources of disorder (defects) lead to the presence of apparent displacements even in the undoped film. The displacements found in the undoped samples were comparable to those in SrTiO 3 reported in the literature [29]. We therefore defined an experimental error cutoff corresponding to the largest displacement found in the undoped sample (see Supplemental Material [28]).…”

“…To improve the signal-to-noise ratio and minimize scan distortions, 20 fast-scan images were recorded, cross-correlated, and then averaged [17]. Position averaged convergent beam diffraction (PACBED) patterns [27], shown in the Supplemental Material [28], were used to reduce the sample tilt to less than 1 mrad from the zone axis, which is important to minimize artifacts in the measured displacements [29]. Absolute column intensities, referenced to the incident beam intensity [16,30,31], were determined by averaging over a circular region with a radius corresponding to a quarter of the lattice constant of SrTiO 3 .…”

Atomic-scale perturbation of oxygen octahedra via surface ion exchange in perovskite nickelates boosts water oxidation

“…ABF-STEM is one of the imaging techniques commonly used for visualizing the position of light elements including oxygen 20,45–50 . However, because atomic columns are imaged in this STEM mode using a dark contrast with a bright background, the position uncertainty of light elements is sometimes not negligible when a specimen is comparatively thick and its tilting angle is high 51,52 . Therefore, to achieve a better signal-to-noise ratio, we used an imaging method, iDPC-STEM, where four-quadrant segmented STEM detectors are utilized for differential phase-contrast image acquisition 30,31 (see Supplementary Fig.…”

Influence of Dislocations in Transition Metal Oxides on Selected Physical and Chemical Properties

“…The electrons at high-angles were scattered nearly from the nuclei and the contrast in HAADF shows the Z 2 -dependence of unscreened Rutherford scattering and the HAADF STEM is called Z-contrast imaging. In this sense, the intensity of HAADF image may be simply described by the straightforward convolution of point spread function P(r p ) and objective function O(r p ): Figure 18b shows the HAADF STEM image of SrTiO 3 viewed along the [001] direction, and one can clearly recognize the locations of Sr and Ti-O atomic columns, as respective bright contrasts [166]. Owing to the Z-contrast nature, the heavier Sr atomic column is brighter than Ti-O atomic column, and therefore Z-contrast imaging can be considered as a chemical sensitive imaging.…”