Ultra-thin NbS₂ nanoflakes grown by sulfurization of niobium oxide films

Niobium disulfide (NbS₂) is one of the few layered transition metal dichalcogenides (TMDs) that exhibit metallic behavior and superconductivity. Atomically thin nanoflakes allow for the study of novel electrical transport properties induced by low dimensionality. Chemical vapor deposition growth of NbS₂ nanoflakes so far has mostly involved corrosive precursors such as NbCl₅ and H₂S which may complicate the synthesis process. In this work, we report on a sulfurization method to synthesize ultra-thin NbS₂ in which the above harsh precursors were avoided. Niobium oxide films were first grown on sapphire substrates by pulsed laser deposition and were subsequently annealed in sulfur atmosphere, yielding NbS₂ nanoflakes with thickness down to bilayer. We will discuss how the electrical properties and Raman vibrational modes change as a function of thickness, stoichiometry and aging.