Realization of Vanadium Sulfide Compounds in the 2D Limit

By comparison with many of the layered transition metal dichalcogenides, VS₂ has been relatively understudied, likely because it is a challenging material to prepare stoichiometrically in the bulk. Moreover, the single layer has not heretofore been isolated. However, the material has intriguing properties in the bulk, including both charge density waves and magnetism.

Here we report the first realization of single-layer VS₂, which we have prepared epitaxially with high quality on Au(111) in the octahedral (1T) structure. Additionally, we find that we can deplete the VS₂ lattice of S by annealing in vacuum so as to create either of two entirely new two-dimensional compounds which have not been previously reported in either the single layer or the bulk. The transitions are reversible upon annealing in a sulfide gas atmosphere. Using a combination of scanning tunneling microscopy, photoemission, and density functional theory, we have made detailed investigation of the structural and electronic properties of all three compounds.