Synthesis of epitaxial monolayer Janus SPtSe

TL;DR

This paper reports the synthesis and structural analysis of a novel Janus monolayer SPtSe, demonstrating a controlled chemical composition change and potential for strong Rashba spin-orbit coupling in 2D materials.

Contribution

It introduces a new Janus monolayer SPtSe synthesized via sulphurization of PtSe2 and provides detailed in situ structural analysis of its formation process.

Findings

Successful synthesis of SPtSe monolayer with ordered structure

Selective substitution of Se by S in the top layer

Recrystallization process preserves crystalline order

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 novel Janus compound, SPtSe, which is predicted to exhibit strong Rashba spin-orbit coupling. We synthetized it by conversion of a single-layer of PtSe$_2$ on Pt(111) via sulphurization under H$_2$S 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 PtSe$_2$ monolayer is first lost due to thermal annealing. A subsequent recrystallization in presence of a source of sulphur yields a highly ordered SPtSe alloy, which is iso-structural to the pristine PtSe$_2$. 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.