Journal
ULTRAMICROSCOPY
Volume 147, Issue -, Pages 8-20Publisher
ELSEVIER
DOI: 10.1016/j.ultramic.2014.05.007
Keywords
ADF-STEM; SAED; Thickness; MoS2; WS2; Tilt
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Funding
- C-SPIN
- MARCO
- DARPA
- NSF [DMR-1006706]
- University of Minnesota Graduate School Fellowship
- Division Of Materials Research
- Direct For Mathematical & Physical Scien [1006706] Funding Source: National Science Foundation
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Multislice simulations were used to analyze the reliability of annular dark field scanning transmission electron microscopy (ADE-STEM) imaging and selected-area electron diffraction (SAED) for determining the thicknesses of MoS2 and WS2 specimens in the aberration-corrected TEM. Samples of 1 to 4 layers in thickness for both 2H and IT polymorphs were studied and tilts up to 500 mrad off of the [0001] zone axis were considered. All thicknesses including the monolayer showed distortions and intensity variations in their ADF-STEM images and SAED patterns as a result of tilt. Both techniques proved to be applicable to distinguish monolayers from multilayers using tilt. Without tilt, neither technique allows unambiguous thickness determination solely by comparing relative intensities of atomic columns in ADE-STEM images or diffraction patterns oriented along at [0001] zone axis, with the exception of monolayer 2H WS2. However, differentiation is possible using absolute intensities in ADF-STEM images. The analysis of ADF-STEM images and SAED patterns also allows identification of the 2H and IT polymorphs of MoS2 and WS2. (C) 2014 Elsevier B.V. All rights reserved.
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