Probing the intrinsic field in few-layer Janus RhSeCl using ARPES

Two-dimensional (2D) Janus transition metal dichalcogenides (TMDs) are a distinctive class of materials characterized by a transition metal layer sandwiched between two different chalcogen layers, breaking the out-of-plane mirror symmetry. In few-layer form, Janus materials are expected to show an intrinsic out-of-plane electric field, driven by the electronegativity difference between the two chalcogen layers. This internal field has been proposed to enable a range of novel phenomena including atomic-scale p–n junctions, passive electrostatic gating, large Berry curvature, and Rashba spin splitting [1-3]. While this effect is robust in density functional theory calculations, its direct experimental observation has remained elusive.

Here, we report the first direct detection and quantification of the intrinsic electric field in few-layer RhSeCl, a newly synthesized Janus semiconductor with exceptionally low chalcogen mixing. We study 2D heterostructures in which exfoliated few-layer RhSeCl is encapsulated between two monolayer graphene sheets. Using angle resolved phototemission (ARPES), we directly probe the charge transfer from the two surfaces of RhSeCl to graphene, demonstrating an atomic-scale p–n junction, where electron- and hole-doped graphene sheets are separated by only ~ 2 nm.

In addition, we present ARPES results from termination-dependent studies of bulk RhSeCl, revealing differences between Cl- and Se-terminated surfaces.

References:

[1] H. Zhao, et al. Preparation, Properties, and Applications of 2D Janus Transition Metal Dichalcogenides. Crystals 2025, 15,567

[2] A. C. Riis-Jensen, et al. J. Phys. Chem. C 2018, 122, 24520−24526

[3] M. Palsgaard, et al. Nano Lett. 2018, 18, 7275−7281