Metallic 2D Janus SNbSe layers driven by a structural phase change†

Abstract

The discovery of two-dimensional (2D) Janus materials has ignited significant research interest, particularly for their distinct properties diverging from their classical 2D transition metal dichalcogenide (TMD) counterparts. While semiconducting 2D Janus TMDs have been demonstrated, examples of metallic Janus layers are still rather limited. Here, we address this gap by experimentally synthesizing and characterizing metallic Janus layers, focusing on SNbSe and SeNbS, derived from monolayer NbS₂ and NbSe₂ using a plasma-assisted technique. Our results show that Nb-based 2D Janus layers form after 1H-to-1T phase transition, marking a phase transition-induced formation of Janus layers. Our comprehensive spectroscopy and microscopy studies, including Z-contrast high angle annular dark field scanning transmission electron microscopy, reveal the phononic and structural properties during Janus SeNbS formation and establish their energetic stability. Density functional theory (DFT) simulations provide insights into the phononic and electronic properties of these materials, shedding light on their potential for diverse applications. Overall, our results demonstrate the realization of niobium-based Janus metals and expand the library of metallic Janus layers.