Stabilization of Metastable 2D Wurtzite MnS via Sulfur Vacancy Engineering.

Metastable wurtzite transition-metal compounds are of interest because their hexagonal symmetry can enable electronic and magnetic behaviors inaccessible to thermodynamically stable phases. Their synthesis in the 2D limit, however, remains challenging. Here, we demonstrate the direct growth of metastable 2D wurtzite MnS nanosheets by atmospheric-pressure chemical vapor deposition via sulfur-vacancy engineering. Ultrathin MnS nanosheets with lateral dimensions of tens of micrometers are grown in a 10 min deposition step. Phase selection is controlled by the cooling atmosphere: interrupting the gas flow after growth creates sulfur-deficient conditions, promotes sulfur-vacancy formation, and stabilizes the wurtzite phase, whereas continuous flow supply yields the stable rock-salt phase. Transmission electron microscopy and grazing-incidence wide-angle X-ray scattering confirm the wurtzite structure, and electron paramagnetic resonance spectroscopy reveals abundant sulfur vacancies. The nanosheets exhibit p-type semiconducting transport, negative magnetoresistance up to room temperature, and a low-temperature exchange-bias effect. These results identify sulfur vacancies as a key determinant of metastable phase stabilization and provide a design principle that may be extendable to other chalcogenide systems.