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 PtSe2 on Pt(111) via sulphurization 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 sulphur yields a highly ordered SPtSe alloy, which is iso-structural 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.
@article{arxiv.2009.08706,
title = {Synthesis of epitaxial monolayer Janus SPtSe},
author = {R. Sant and M. Gay and A. Marty and S. Lisi and R. Harrabi and C. Vergnaud and M. T. Dau and X. Weng and J. Coraux and N. Gauthier and O. Renault and G. Renaud and M. Jamet},
journal= {arXiv preprint arXiv:2009.08706},
year = {2020}
}