Aberration-corrected STEM imaging of 2D materials: Artifacts and practical applications of threefold astigmatism

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Science Advances  09 Sep 2020:
Vol. 6, no. 37, eabb8431
DOI: 10.1126/sciadv.abb8431
  • Fig. 1 Schematic illustration of the emergence of RMC as a result of the mutual orientations between A2 (red arrows) and MoS2 (green arrows).

    (A) Computer-generated atomic models of monolayer MoS2 with a mirror grain boundary. (B) Schematic representations of the dissimilar atomic configurations where S contrast degrades on LHS, and enhancement in S contrast is observed on RHS. (C) Simulation of HR-STEM ADF imaging for the atomic models in (A) with A2 applied.

  • Fig. 2 QSTEM simulation of HR-STEM ADF imaging.

    Domains of 2D monolayer MoS2 separated with an antiphase (60° or 180° in-plane rotation) growth mismatch for Cs-corrected electron probe with various A2. (A) Image taken from QSTEM simulation based on the atomic model in (B) with A2 = 0 nm. (C) Schematics of A2 orientation effect on S contrast. (D to L) Same as in (A) but with different values and orientations of A2 introduced. Insets in (A) and (D) to (L) show the relative magnitude and orientations of A2 (red arrows) and the attendant evolution of the electron probe shape.

  • Fig. 3 Experimental observations of RMC in HR-STEM ADF imaging.

    (A to D) Sample rotation experiment: HR-STEM ADF imaging taken at regions in close proximity to the interface between MoS2 mirror grains with an antiphase (60°) growth mismatch. Schematic representation of the relative position of sample supported on TEM holder before and after rotation is illustrated in (A) and (C). Corresponding HR-STEM ADF images before and after an in-plane rotation by 60° are shown in (B) and (D). The experimental observation agrees very well with the QSTEM simulation results as is evident by the atomically resolved phase transition after A2 rotation. (E to H) A2 rotation experiment: Cs-corrected HR-STEM ADF imaging of the interface between a monolayer MoS2 grains with antiphase (60°) growth mismatch. (E and F) Images at the same spot of the interface before and after A2 = 100-nm rotation by 60°, correspondingly. Atomic models (yellow for Mo and green for S) and arrows (green for sulfur and red for A2) suggest A2 orientation based on the simulation in Fig. 2. (G) Image of the interface for A2 reduced below the detection limit, and (H) additionally, monochromated beam (60-meV energy spread) was used. Scale bars, 1 nm.

  • Fig. 4 Electron beam–induced local transition of embedded patch inside MoS2 matrix.

    False-colored HR-STEM ADF images at a mirror grain boundary. (A) Before and (B) after A2 = 100 nm and rotating by 60°, respectively. Color coding is used to distinguish regions with 2H (red) and false 1T (yellow) types of contrast, caused by (A2↓ - S↑) and (A2↑ - S↑) imaging configuration, respectively. Red and yellow triangles in (A) and (B) show the growing 2H (S↑) transition region in 2H (S↓) matrix. Note that white arrows denote double S vacancy sites. The inset in (B) shows the simulation of false 1T contrast of MoS2 film with a double S vacancy in the center. Scale bar, 1 nm. (C) Schematic representations reveal the root cause of contrast formation in both (A) and (B).

Supplementary Materials

  • Supplementary Materials

    Aberration-corrected STEM imaging of 2D materials: Artifacts and practical applications of threefold astigmatism

    Sergei Lopatin, Areej Aljarb, Vladimir Roddatis, Tobias Meyer, Yi Wan, Jui-Han Fu, Mohamed Hedhili, Yimo Han, Lain-Jong Li, Vincent Tung

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