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Ultramicroscopy. 2017 Jan;172:17-29. doi: 10.1016/j.ultramic.2016.10.007. Epub 2016 Oct 18.

Three-dimensional imaging of individual point defects using selective detection angles in annular dark field scanning transmission electron microscopy.

Author information

1
Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43212, USA.
2
Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43212, USA. Electronic address: hwang.458@osu.edu.

Abstract

We propose a new scanning transmission electron microscopy (STEM) technique that can realize the three-dimensional (3D) characterization of vacancies, lighter and heavier dopants with high precision. Using multislice STEM imaging and diffraction simulations of β-Ga2O3 and SrTiO3, we show that selecting a small range of low scattering angles can make the contrast of the defect-containing atomic columns substantially more depth-dependent. The origin of the depth-dependence is the de-channeling of electrons due to the existence of a point defect in the atomic column, which creates extra "ripples" at low scattering angles. The highest contrast of the point defect can be achieved when the de-channeling signal is captured using the 20-40mrad detection angle range. The effect of sample thickness, crystal orientation, local strain, probe convergence angle, and experimental uncertainty to the depth-dependent contrast of the point defect will also be discussed. The proposed technique therefore opens new possibilities for highly precise 3D structural characterization of individual point defects in functional materials.

KEYWORDS:

Atomic scale 3D information; Electron channeling; Point defects; Scanning transmission electron microscopy

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