Intra-Domain Periodic Defects in Monolayer MoS$_2$

TL;DR

This study uses high-resolution STM to reveal periodic intra-domain defects in CVD-grown monolayer MoS2, uncovering structural features hidden from optical microscopy and proposing a growth mechanism for these defects.

Contribution

It provides the first detailed atomic-scale characterization of intra-domain periodic defects in monolayer MoS2 and links these features to the growth process.

Findings

Periodic defects are about 50 nm apart and a few nanometers wide.

Defects are visible only with high-resolution STM, not optical microscopy.

A complex growth mechanism explains the formation of these defects.

Abstract

We present an ultra-high vacuum scanning tunneling microscopy (STM) study of structural defects in molybdenum disulfide thin films grown on silicon substrates by chemical vapor deposition. A distinctive type of grain boundary periodically arranged inside an isolated triangular domain, along with other inter-domain grain boundaries of various types, is observed. These periodic defects, about 50 nm apart and a few nanometers in width, remain hidden in optical or low-resolution microscopy studies. We report a complex growth mechanism that produces 2D nucleation and spiral growth features that can explain the topography in our films.