Van der Waals interfacial reconstruction in monolayer transition-metal dichalcogenides and gold heterojunctions

Wen Wu Xu,Xiaodong Wang,Ruichun Luo,Ziqian Wang,Yi Gao,Pan Liu,Mingwei Chen,Yongzheng Zhang

doi:10.1038/s41467-020-14753-8

Abstract

The structures and properties of van der Waals (vdW) heterojunctions between semiconducting two-dimensional transition-metal dichalcogenides (2D TMDs) and conductive metals, such as gold, significantly influence the performances of 2D-TMD based electronic devices. Chemical vapor deposition is one of the most promising approaches for large-scale synthesis and fabrication of 2D TMD electronics with naturally formed TMD/metal vdW interfaces. However, the structure and chemistry of the vdW interfaces are less known. Here we report the interfacial reconstruction between TMD monolayers and gold substrates. The participation of sulfur leads to the reconstruction of Au {001} surface with the formation of a metastable Au4S4 interfacial phase which is stabilized by the top MoS2 and WS2 monolayers. Moreover, the enhanced vdW interaction between the reconstructed Au4S4 interfacial phase and TMD monolayers results in the transition from n-type TMD-Au Schottky contact to p-type one with reduced energy barrier height.

Highlights

The structures and properties of van der Waals heterojunctions between semiconducting two-dimensional transition-metal dichalcogenides (2D TMDs) and conductive metals, such as gold, significantly influence the performances of 2D-TMD based electronic devices
Chemical vapor deposition (CVD) is a welldeveloped method to grow high quality 2D materials and to fabricate electronic devices on various substrates18, which provides the possibility to directly obtain perfect van der Waals (vdW) contacts with metals, like graphene grown on Cu (111) surface19 and hBN grown on Cu (110) surface20
MoS2 was grown on a 100 nm thick nanoporous gold (NPG) film, which was prepared by chemical dealloying33, by a low-pressure chemical vapor deposition (CVD) method (Supplementary Fig. 1)34

Summary

Introduction

The structures and properties of van der Waals (vdW) heterojunctions between semiconducting two-dimensional transition-metal dichalcogenides (2D TMDs) and conductive metals, such as gold, significantly influence the performances of 2D-TMD based electronic devices. Chemical vapor deposition is one of the most promising approaches for large-scale synthesis and fabrication of 2D TMD electronics with naturally formed TMD/metal vdW interfaces. Atomic scale characterization of the interfaces by scanning transmission electron microscopy (STEM) has suggested that the degradation is associated with the damage of TMDs in the contact layer by invasion of metal atoms. Atomic scale characterization of the interfaces by scanning transmission electron microscopy (STEM) has suggested that the degradation is associated with the damage of TMDs in the contact layer by invasion of metal atoms12–14 Interface engineering, such as insertion of additional vdW layers (graphene, hexagonal boron nitride (hBN), etc.), mechanical transfer of metal films and incorporation with indium, are explored to form ideal vdW contacts that are free from the chemical disorder.

Methods

Results

Conclusion