Misorientation-angle-dependent electrical transport across molybdenum disulfide grain boundaries.

Thuc Hue Ly,Sang Hoon Chae,Jiong Zhao,Hye Yun Jeong,Hyun Kim,David J Perello,Young Hee Lee,Qingming Deng,Gang Hee Han

doi:10.1038/ncomms10426

Abstract

Grain boundaries in monolayer transition metal dichalcogenides have unique atomic defect structures and band dispersion relations that depend on the inter-domain misorientation angle. Here, we explore misorientation angle-dependent electrical transport at grain boundaries in monolayer MoS2 by correlating the atomic defect structures of measured devices analysed with transmission electron microscopy and first-principles calculations. Transmission electron microscopy indicates that grain boundaries are primarily composed of 5–7 dislocation cores with periodicity and additional complex defects formed at high angles, obeying the classical low-angle theory for angles <22°. The inter-domain mobility is minimized for angles <9° and increases nonlinearly by two orders of magnitude before saturating at ∼16 cm2 V−1 s−1 around misorientation angle≈20°. This trend is explained via grain-boundary electrostatic barriers estimated from density functional calculations and experimental tunnelling barrier heights, which are ≈0.5 eV at low angles and ≈0.15 eV at high angles (≥20°).

Highlights

Grain boundaries in monolayer transition metal dichalcogenides have unique atomic defect structures and band dispersion relations that depend on the inter-domain misorientation angle
On using density functional theory (DFT) to calculate the a-dependent local grain boundaries (GBs) band structures, equilibrium electrostatic GB barriers were found to be correlated with experimentally determined barriers, which gives a clear understanding of the underlying mobility dependences
To suppress interaction with oxygen-related functional groups, further device fabrication was performed in a glove box (H2O, O2o1 p.p.m.) and only acetone solvent was used during the electron-beam lithography procedures to minimize additional GB functionalization

Summary

Introduction

Grain boundaries in monolayer transition metal dichalcogenides have unique atomic defect structures and band dispersion relations that depend on the inter-domain misorientation angle. The inter-domain mobility is minimized for angles o9° and increases nonlinearly by two orders of magnitude before saturating at B16 cm[2] V À 1 s À 1 around misorientation angleE20° This trend is explained via grain-boundary electrostatic barriers estimated from density functional calculations and experimental tunnelling barrier heights, which are E0.5 eV at low angles and E0.15 eV at high angles (Z20°). Experimental assessment of MoS2 GB transport is still under debate in the literature[6,7,8,9,10,11] due to a large device-to-device performance variation, poor single-domain carrier mobility, and, most importantly, lack of correlation between transport properties and GB atomic structures We overcome these difficulties by directly correlating four-probe transport measurements across single GBs with both high-resolution transmission electron microscopy (TEM) imaging of the measured devices and first-principles calculations. On using DFT to calculate the a-dependent local GB band structures, equilibrium electrostatic GB barriers were found to be correlated with experimentally determined barriers, which gives a clear understanding of the underlying mobility dependences

Methods

Results

Conclusion