Atomic electrostatic maps of 1D channels in 2D semiconductors using 4D scanning transmission electron microscopy

Grace G D Han,Christopher S Allen,Colin Ophus,Jamie H Warner,Yi Wen,Angus I Kirkland,Shiang Fang,Efthimios Kaxiras

doi:10.1038/s41467-019-08904-9

Abstract

Defects in materials give rise to fluctuations in electrostatic fields that reflect the local charge density, but imaging this with single atom sensitivity is challenging. However, if possible, this provides information about the energetics of adatom binding, localized conduction channels, molecular functionality and their relationship to individual bonds. Here, ultrastable electron-optics are combined with a high-speed 2D electron detector to map electrostatic fields around individual atoms in 2D monolayers using 4D scanning transmission electron microscopy. Simultaneous imaging of the electric field, phase, annular dark field and the total charge in 2D MoS2 and WS2 is demonstrated for pristine areas and regions with 1D wires. The in-gap states in sulphur line vacancies cause 1D electron-rich channels that are mapped experimentally and confirmed using density functional theory calculations. We show how electrostatic fields are sensitive in defective areas to changes of atomic bonding and structural determination beyond conventional imaging.

Highlights

Defects in materials give rise to fluctuations in electrostatic fields that reflect the local charge density, but imaging this with single atom sensitivity is challenging
The x and y components of the experimental ICoM can be used to calculate the momentum transfer and the probe convoluted electric field components (Ex┴ and Ey┴). These are directly compared to the Density functional theory (DFT) calculated values and we typically find the experimental values being half that of the DFT
The total magnitude of the probe convolved electric field E┴ is calculated, |E┴|, plotted for comparison with the DFT calculations for MoS2 (Fig. 1j–l) showing triangular symmetry due to the hexagonal lattice of MoS2, and the absence of |E┴| in the center of each triangle corresponds to the location of the nucleus

Summary

Introduction

Defects in materials give rise to fluctuations in electrostatic fields that reflect the local charge density, but imaging this with single atom sensitivity is challenging. Density functional theory (DFT) calculations show that as the width of the S line vacancies increases from 1S to 2S, the band gap narrows from 1.9 to

Methods

Results

Conclusion