Determining the thickness of atomically thin MoS2 and WS2 in the TEM

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Abstract

Multislice simulations were used to analyze the reliability of annular dark field scanning transmission electron microscopy (ADF-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 1T polymorphs were studied and tilts up to 500mrad 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 ADF-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 1T polymorphs of MoS2 and WS2.

Original languageEnglish (US)
Pages (from-to)8-20
Number of pages13
JournalUltramicroscopy
Volume147
DOIs
StatePublished - Dec 2014

Bibliographical note

Funding Information:
This work was supported in part by C-SPIN, one of the six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA and by the NSF under award number DMR-1006706 , and the University of Minnesota Graduate School Fellowship . We also acknowledge receiving access to computational resources from the University of Minnesota Supercomputing Institute.

Keywords

  • ADF-STEM
  • SAED
  • Thickness
  • Tilt

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