Temperature-Triggered Sulfur Vacancy Evolution in Monolayer MoS₂ /Graphene Heterostructures

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Defects in 2D semiconductors significantly impact their electronic and optoelectronic properties.
• Molybdenum disulfide (MoS2) is a key 2D material with potential applications in electronics.

Purpose of the Study:

• To investigate the formation and impact of defects in monolayer MoS2.
• To explore defect engineering for modulating the electronic properties of 2D semiconductors.

Main Methods:

• Chemical vapor deposition (CVD) for MoS2 synthesis.
• Annealing under ultrahigh vacuum (UHV) conditions at different temperatures (≈400 K and ≈900 K).
• Scanning tunneling microscopy (STM) and spectroscopy (STS) for defect characterization.
• First-principles theoretical simulations.

Main Results:

• Monolayer MoS2 prepared by CVD is nearly defect-free after annealing at ≈400 K.
• Annealing at ≈900 K introduces dominant single sulfur vacancies and vacancy chains (2S, 3S, 4S) in MoS2 on Au foils.
• Vacancies decrease the bandgap and induce n-doping in monolayer MoS2.
• Experimental results are consistent with theoretical simulations.

Conclusions:

• Defect engineering via controlled annealing is a viable strategy to tune the electronic properties of 2D semiconductors.
• Sulfur vacancies in MoS2 offer a pathway for modulating its band structure and achieving n-doping.
• This work provides a novel route for defect engineering in 2D layered materials.