Atomic-Scale Spectroscopy of Gated Monolayer MoS2

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanoscience

Background:

• Monolayer transition-metal dichalcogenides exhibit tunable electronic properties via electrostatic gating.
• Atomic-resolution scanning tunneling microscopy/spectroscopy (STM/STS) is crucial for probing nanoscale electronic behavior.

Purpose of the Study:

• To investigate the gate-tunable electronic properties of semiconducting monolayer molybdenum disulfide (MoS2).
• To characterize in-gap states and exciton binding energy in MoS2 using advanced spectroscopic techniques.

Main Methods:

• Large-area MoS2 monolayers grown by metal-organic chemical vapor deposition (MOCVD) on silicon oxide substrates.
• Atomic-resolution STM/STS measurements to probe topography and electronic structure.
• Gate voltage-dependent spectroscopy to analyze electronic property tuning.

Main Results:

• Identified in-gap states in MoS2 with a density of 1.3 × 10^12 eV⁻¹ cm⁻².
• Estimated an exciton binding energy of 230 meV for MoS2 on a silicon oxide substrate.
• Observed grain boundaries in polycrystalline MoS2 samples, noting their minimal electronic impact in STM imaging.

Conclusions:

• Electrostatic gating effectively tunes the electronic properties of monolayer MoS2.
• The study quantifies key electronic parameters, including in-gap states and exciton binding energy.
• MoS2 quality is comparable to single crystals, with grain boundaries having limited electronic influence on STM scans.