Phase engineering in tantalum sulfide monolayers on Au(111)

TL;DR

This study demonstrates the controlled growth and structural analysis of tantalum sulfide monolayers on Au(111), revealing phase engineering, layer alignment, and heterostructure formation with atomically precise boundaries.

Contribution

It introduces a growth process for oriented 2H-TaS$_2$ monolayers on Au(111) and provides detailed structural insights using STM and DFT, enabling phase control and heterostructure engineering.

Findings

Successful preparation of 2H-TaS$_2$ and TaS monolayers on Au(111)

Identification of layer registry and domain structures via STM and DFT

Formation of lateral heterostructures with defect-free boundaries

Abstract

We prepare monolayers of tantalum sulfide on Au(111) by evaporation of Ta in a reactive background of H$_2$S. Under sulfur-rich conditions, monolayers of 2H-TaS$_2$ develop, whereas under sulfur-poor conditions TaS forms, a structure that can be derived from 2H-TaS$_2$ by removal of the bottom S layer. We analyse the alignment of the layers with respect to the substrate and the relation with the domains in the Au(111) herringbone reconstruction using scanning tunneling microscopy (STM). With the help of density functional theory (DFT) calculations we can determine the registry of the two phases with the substrate. We develop a growth process that allows preparation of uniquely oriented 2H-TaS$_2$ on Au(111). 2H-TaS$_2$ and TaS have a remarkably similar in-plane lattice structure and we observe the formation of lateral 2H-TaS$_2$-TaS heterostructures with atomically well-defined and defect-free boundaries. We observe mirror twin boundaries within 2H-TaS$_2$ along the S- and Ta-edge.