Exploiting Native Defects in Molybdenum Disulfide (MoS₂) monolayers

The growth dynamics of MoS₂ films synthesized via Chemical Vapor Deposition (CVD) were systematically investigated, with particular focus on the influence of sulfur (S) concentration and chamber pressure on the resulting crystal morphology. The study also includes a comprehensive analysis of intrinsic point defect formation in monolayer MoS₂ films. Defect concentrations were evaluated by calculating their formation energies as a function of sulfur vapor pressure, across a broad range of experimental conditions spanning from Mo-rich to S-rich regimes.

Given that CVD growth typically occurs under non-stoichiometric conditions —either with excess or deficient sulfur—the investigation primarily targets sulfur vacancies (V_S), molybdenum vacancies (V_Mo), and their charged counterparts. Building on the theoretical determination of a minimum sulfur partial pressure required for defect-free growth, experimental results confirmed that perfectly triangular MoS₂ domains—with Mo-terminated zigzag (Mo-zz) edges—form when the Mo:S ratio is optimized.

Film crystallinity and structural quality were characterized using X-ray diffraction (XRD) and Raman spectroscopy. Notably, significant shifts were observed in the E_2g¹ and A_1g Raman modes between films grown under optimal and high sulfur vapor pressures. Electrical measurements performed on gated MoS₂ films grown under optimized conditions revealed promising electronic performance, with carrier concentrations of the order of 10¹² cm^-2 and electron mobility reaching 21 cm²/V·s.