Synthesis of Epitaxial Single-Layer MoS$_2$ on Au(111)

TL;DR

This paper reports a controlled method for synthesizing large-area epitaxial single-layer MoS$_2$ on Au(111) in ultrahigh vacuum, analyzing growth dynamics, domain structures, and electronic properties.

Contribution

It introduces a cycle-based growth technique for high-quality epitaxial MoS$_2$ on Au(111) with detailed structural and electronic characterization.

Findings

Successful synthesis of large-area epitaxial single-layer MoS$_2$

Identification of domain boundaries and bilayer formation

Significant band structure changes observed between mono- and bilayer MoS$_2$

Abstract

We present a method for synthesizing large area epitaxial single-layer MoS$_2$ on the Au(111) surface in ultrahigh vacuum. Using scanning tunneling microscopy and low energy electron diffraction, the evolution of the growth is followed from nanoscale single-layer MoS$_2$ islands to a continuous MoS$_2$ layer. An exceptionally good control over the MoS$_2$ coverage is maintained using an approach based on cycles of Mo evaporation and sulfurization to first nucleate the MoS$_2$ nano-islands and then gradually increase their size. During this growth process the native herringbone reconstruction of Au(111) is lifted as shown by low energy electron diffraction measurements. Within these MoS$_2$ islands, we identify domains rotated by 60$^{\circ}$ that lead to atomically sharp line defects at domain boundaries. As the MoS$_2$ coverage approaches the limit of a complete single-layer, the formation of bilayer MoS$_2$ islands is initiated. Angle-resolved photoemission spectroscopy measurements of both single and bilayer MoS$_2$ samples show a dramatic change in their band structure around the center of the Brillouin zone. Brief exposure to air after removing the MoS$_2$ layer from vacuum is not found to affect its quality.