Sulfurization of NbTe₄ Nanoparticles to Form NbS₂/NbTe₄ Heterostructures

Niobium tetratelluride (NbTe₄) is a pseudo-one-dimensional (1D) material that exhibits fascinating electrical properties, and as a result it has been studied as a superconductor, charge density wave conductor, and phase change material. Traditionally, NbTe₄ has been synthesized through high temperature solid state reactions and thin film sputtering followed by thermal annealing, but we have demonstrated a low temperature solvothermal synthesis that results in nanocrystalline NbTe₄ particles through a diffusion-mediated formation pathway. Conversely, niobium disulfide (NbS₂) is a two-dimensional (2D) metallic material that has also been studied as a superconductor. Traditionally, it has been synthesized through chemical vapor deposition, solvothermally, and through high temperature solid state reactions. Here, we demonstrate a novel approach of synthesizing NbS₂ through the conversion of pseudo-1D NbTe₄ nanoparticles to 2D NbS₂. By heating the NbTe₄ below its melting point in an Ar and H₂S environment, the tellurium is removed and replaced by sulfur to partially or fully convert to NbS_2, while retaining the original rectangular morphology of the nanoparticles. Additionally, we probed heterostructure formation to better understand how the telluride to sulfide conversion is taking place. We utilized X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy to determine the composition and heterostructure stoichiometry. This method demonstrates a facile way to synthesize rectangular particles of NbS₂ and NbS₂/NbTe₄ heterostructures. Our results could potentially be transferred to forming other nanoparticle-2D material heterostructures.