Stoichiometric Control of Structural Phases in Two-Dimensional NbS2 Nanoflakes

Two-dimensional transition metal dichalcogenides (TMDs) are known to exist in multiple structural phases (1T, 2H, and 3R etc.) each with distinct physical properties. The ability to tune the crystal structures in a controlled manner provides an effective route to engineer the respective properties and is therefore of significant technological importance. In this study, we use NbS₂ nanoflakes as an example to demonstrate the control of structural phases in layered TMDs by tuning their stoichiometry. The as-grown NbS₂ has a rhombohedral 3R phase which can be readily transformed into another structure via a simple annealing process. By varying the annealing conditions, we realize several different structural phases as identified by Raman spectroscopy. The reversibility and the underlying mechanism of phase transformations are also studied.