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Thickness and Stacking Sequence Determination of Exfoliated Dichalcogenides (1T-TaS2, 2H-MoS2) Using Scanning Transmission Electron Microscopy

Published online by Cambridge University Press:  03 September 2018

Robert Hovden*
Affiliation:
School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA Department of Materials Science & Engineering, University of Michigan, Ann Arbor, MI48109, USA
Pengzi Liu
Affiliation:
School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA
Noah Schnitzer
Affiliation:
Department of Materials Science & Engineering, University of Michigan, Ann Arbor, MI48109, USA
Adam W. Tsen
Affiliation:
Department of Chemistry, University of Waterloo, Waterloo, ON, Canada, N2L 3G1
Yu Liu
Affiliation:
Key Laboratory of Materials Physics, Chinese Academy of Sciences, Hefei 230031, China
Wenjian Lu
Affiliation:
Key Laboratory of Materials Physics, Chinese Academy of Sciences, Hefei 230031, China
Yuping Sun
Affiliation:
Key Laboratory of Materials Physics, Chinese Academy of Sciences, Hefei 230031, China High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031, China Centre of Advanced Microstructures, Nanjing University, Nanjing, 210093, China
Lena F. Kourkoutis
Affiliation:
School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY 14853, USA
*
*Authors for correspondence: Robert Hovden, E-mail: hovden@umich.edu; Lena Kourkoutis, lena.f.kourkoutis@cornell.edu
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Abstract

Layered transition metal dichalcogenides (TMDs) have attracted interest due to their promise for future electronic and optoelectronic technologies. As one approaches the two-dimensional (2D) limit, thickness and local topology can greatly influence the macroscopic properties of a material. To understand the unique behavior of TMDs it is therefore important to identify the number of atomic layers and their stacking in a sample. The goal of this work is to extract the thickness and stacking sequence of TMDs directly by matching experimentally recorded high-angle annular dark-field scanning transmission electron microscope images and convergent-beam electron diffraction (CBED) patterns to quantum mechanical, multislice scattering simulations. Advantageously, CBED approaches do not require a resolved lattice in real space and are capable of neglecting the thickness contribution of amorphous surface layers. Here we demonstrate the crystal thickness can be determined from CBED in exfoliated 1T-TaS2 and 2H-MoS2 to within a single layer for ultrathin ≲9 layers and ±1 atomic layer (or better) in thicker specimens while also revealing information about stacking order—even when the crystal structure is unresolved in real space.

Type
Materials Science Applications
Copyright
© Microscopy Society of America 2018 

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