Imaging the electron charge density in monolayer MoS2 at the Ångstrom scale

Joel Martis; Sandhya Susarla; Archith Rayabharam; Cong Su; Timothy Paule; Philipp Pelz; Cassandra Huff; Xintong Xu; Hao-Kun Li; Marc Jaikissoon; Victoria Chen; Eric Pop; Krishna Saraswat; Alex Zettl; Narayana R Aluru; Ramamoorthy Ramesh; Peter Ercius; Arun Majumdar

doi:10.1038/s41467-023-39304-9

Imaging the electron charge density in monolayer MoS₂ at the Ångstrom scale

Nat Commun. 2023 Jul 20;14(1):4363. doi: 10.1038/s41467-023-39304-9.

Authors

Joel Martis^#¹, Sandhya Susarla^#^{2

3

4}, Archith Rayabharam⁵, Cong Su^{6

7

8}, Timothy Paule^{6

7

8}, Philipp Pelz^{2

9}, Cassandra Huff¹⁰, Xintong Xu¹, Hao-Kun Li¹, Marc Jaikissoon¹⁰, Victoria Chen¹⁰, Eric Pop¹⁰, Krishna Saraswat¹⁰, Alex Zettl^{6

7

8}, Narayana R Aluru¹¹, Ramamoorthy Ramesh^{6

7}, Peter Ercius¹², Arun Majumdar¹³

Affiliations

¹ Department of Mechanical Engineering, Stanford University, Stanford, CA, USA.
² The National Center for Electron Microscopy (NCEM), The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
³ Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
⁴ School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, USA.
⁵ Department of Mechanical Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
⁶ Department of Physics, University of California Berkeley, Berkeley, CA, USA.
⁷ Department of Materials Science and Engineering, University of California Berkeley, Berkeley, CA, USA.
⁸ Kavli Energy NanoScience Institute, University of California Berkeley, Berkeley, CA, USA.
⁹ Institute of Micro- and Nanostructure Research & Center for Nanoanalysis and Electron Microscopy (CENEM), Department of Materials Science, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany.
¹⁰ Department of Electrical Engineering, Stanford University, Stanford, CA, USA.
¹¹ Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX, USA.
¹² The National Center for Electron Microscopy (NCEM), The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. percius@lbl.gov.
¹³ Department of Mechanical Engineering, Stanford University, Stanford, CA, USA. amajumdar@stanford.edu.

^# Contributed equally.

Abstract

Four-dimensional scanning transmission electron microscopy (4D-STEM) has recently gained widespread attention for its ability to image atomic electric fields with sub-Ångstrom spatial resolution. These electric field maps represent the integrated effect of the nucleus, core electrons and valence electrons, and separating their contributions is non-trivial. In this paper, we utilized simultaneously acquired 4D-STEM center of mass (CoM) images and annular dark field (ADF) images to determine the projected electron charge density in monolayer MoS₂. We evaluate the contributions of both the core electrons and the valence electrons to the derived electron charge density; however, due to blurring by the probe shape, the valence electron contribution forms a nearly featureless background while most of the spatial modulation comes from the core electrons. Our findings highlight the importance of probe shape in interpreting charge densities derived from 4D-STEM and the need for smaller electron probes.