Large Work Function Modulation of Monolayer MoS2 by Ambient Gases.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanoscience

Background:

• Two-dimensional (2D) monolayer transition-metal dichalcogenides (TMDs) exhibit unique properties not found in bulk materials.
• Environmental factors can obscure the intrinsic properties of 2D materials, impacting their performance in electronic devices.
• Work function is a critical parameter for electronic and optoelectronic devices, representing the energy needed to extract an electron.

Purpose of the Study:

• To investigate the modulation of work function in molybdenum disulfide (MoS2) due to ambient gases.
• To understand the environmental effects on the electronic properties of 2D materials.
• To explore the potential of work function tuning for device applications.

Main Methods:

• In situ Kelvin probe technique for work function measurement.
• Ultraviolet photoemission spectroscopy (UPS) for confirmation.
• Theoretical calculations to support experimental findings.
• Fabrication of homojunction diodes by partial passivation of transistors.
• Photocurrent mapping to estimate depletion width.

Main Results:

• A significant work function modulation in MoS2 was observed with exposure to ambient gases, specifically oxygen (O2).
• The work function increased from 4.04 eV in vacuum to 4.47 eV upon O2 exposure, comparable to variations in graphene.
• Fabricated homojunction diodes exhibited ideal characteristics with an ideality factor close to one and perfect electrical reversibility.
• The estimated depletion width was approximately 200 nm, considerably narrower than in bulk semiconductors.

Conclusions:

• Ambient oxygen plays a critical role in modulating the work function of MoS2.
• The observed work function changes are substantial and can be leveraged for tuning electronic properties.
• The narrow depletion width in MoS2 devices suggests potential for high-performance nanoelectronic applications.