Synthesis of epitaxial monolayer Janus SPtSe

Roberto Sant,Gilles Renaud,Céline Vergnaud,Alain Marty,Maxime Gay,Minh Tuan Dau,Olivier Renault,Rania Harrabi,Xiaorong Weng,Simone Lisi,Matthieu Jamet,Nicolas Gauthier,Johann Coraux

doi:10.1038/s41699-020-00175-z

Abstract

Janus single-layer transition metal dichalcogenides, in which the two chalcogen layers have a different chemical nature, push chemical composition control beyond what is usually achievable with van der Waals heterostructures. Here, we report such a Janus compound, SPtSe, which is predicted to exhibit strong Rashba spin–orbit coupling. We synthetized it by conversion of a single-layer of PtSe2 on Pt(111) via sulfurization under H2S atmosphere. Our in situ and operando structural analysis with grazing incidence synchrotron X-ray diffraction reveals the process by which the Janus alloy forms. The crystalline long-range order of the as-grown PtSe2 monolayer is first lost due to thermal annealing. A subsequent recrystallization in presence of a source of sulfur yields a highly ordered SPtSe alloy, which is isostructural to the pristine PtSe2. The chemical composition is resolved, layer-by-layer, using angle-resolved X-ray photoelectron spectroscopy, demonstrating that Se-by-S substitution occurs selectively in the topmost chalcogen layer.

Highlights

Most electronic properties of crystals are inherited from their symmetries
For monolayer transition metal dichalcogenides (TMDCs) in the 1H phase like MX2 (M=Mo,W and X=S, Se), the mirror symmetry with respect to the transition metal atoms plane leads to zero internal out-of-plane electric field and suppresses any Rashba spin–orbit coupling (SOC)
Before we address the formation and structure of the Janus alloy, we discuss about its parent compound, the pristine single layer (SL) PtSe2

Summary

Introduction

Most electronic properties of crystals are inherited from their symmetries. For monolayer transition metal dichalcogenides (TMDCs) in the 1H phase like MX2 (M=Mo,W and X=S, Se), the mirror symmetry with respect to the transition metal atoms plane leads to zero internal out-of-plane electric field and suppresses any Rashba spin–orbit coupling (SOC). Most superstructure peaks (except those of PtSe2 with h and k multiple of 3), are located close to integer values of l (see e.g., (50l) rod in UHV a few tens of degrees above the growth temperature (between 370 °C and 400 ° C), in order to create Se vacancies in the topmost chalcogen layer, which will be eventually filled with S atoms.

Results

Conclusion