Healing Atom Vacancy and Oxidation Suppression in Solution-Processed MoS₂ through Sulfur Vapor Annealing

Sulfur vacancies and interface oxidation are the major challenging issues causing degradation of the structural and electronic properties of molybdenum disulfide (MoS₂). This study demonstrates a sulfur vapor annealing technique to restore sulfur vacancies and suppress oxidation in solution-processed MoS₂ films on Si₃N₄ surfaces. MoS₂ films deposited with precursor concentrations ranging from 5 to 40 mM were annealed at 700 °C under argon (Ar) and sulfur vapor (S-vapor) atmospheres. High-resolution transmission electron microscopy (HRTEM) reveals enhanced crystallinity and a well-ordered layered structure with an interlayer space of ∼0.65 nm in S-vapor-annealed films, compared to disordered and defect structures in Ar-annealed counterparts. X-ray photoelectron spectroscopy (XPS) confirms a near-stoichiometric S/Mo ratio (∼2:1) and a consistently low Mo⁶⁺/Mo⁴⁺ ratio (∼0.1-0.15), suggesting minimal oxidation and stable Mo⁴⁺ states in S-vapor-annealed films. Thermal desorption spectroscopy (TDS) analysis displays increased SO (m/z = 48) and SO₂ desorption (m/z = 64) in S-vapor-annealed films, especially at higher precursor concentrations, indicating increased sulfur incorporation. The results demonstrate sulfur vapor annealing to be a very effective post-treatment technique to improve the structural integrity and chemical stability of solution-processed MoS₂ films for high-performance electronic devices.