Four-dimensional scanning transmission electron microscopy (4D-STEM) has recently gained widespread attention for its ability to image atomic electric fields with sub-{\AA}ngstrom 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 electron charge density in monolayer MoS2. We find that both the core electrons and the valence electrons contribute 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.
@article{arxiv.2210.09478,
title = {Imaging the electron charge density in monolayer MoS2 at the {\AA}ngstrom scale},
author = {Joel Martis and Sandhya Susarla and Archith Rayabharam and Cong Su and Timothy Paule and Philipp Pelz and Cassandra Huff and Xintong Xu and Hao-Kun Li and Marc Jaikissoon and Victoria Chen and Eric Pop and Krishna Saraswat and Alex Zettl and Narayana R. Aluru and Ramamoorthy Ramesh and Peter Ercius and Arun Majumdar},
journal= {arXiv preprint arXiv:2210.09478},
year = {2023}
}