Exciton-dominated Dielectric Function of Atomically Thin MoS2 Films.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Optoelectronics

Background:

• The dielectric function of materials governs their interaction with light.
• Atomically thin transition metal dichalcogenides, like molybdenum disulfide (MoS2), are promising for next-generation electronics and photonics.
• Understanding layer-dependent optical properties is crucial for device applications.

Purpose of the Study:

• To systematically investigate the dielectric function of MoS2 films across various layer numbers.
• To elucidate the role of excitonic effects versus band structure in determining the dielectric properties.
• To extract exciton binding energies and Bohr radii in few-layer MoS2.

Main Methods:

• Systematic measurement of the dielectric function of MoS2 films with varying layer numbers.
• Analysis of the layer-dependent dielectric function, identifying anomalous behavior.
• Fitting experimental data with a model to extract exciton parameters.

Main Results:

• Excitonic effects are dominant in MoS2 films with fewer than 5-7 layers.
• An anomalous layer-dependent dielectric function was observed: decreasing with layer number for thin films and increasing for thicker films.
• Layer-dependent exciton binding energy and Bohr radius were extracted.

Conclusions:

• Excitonic contributions to the dielectric function can surpass band structure contributions in few-layer MoS2.
• This layer-dependent behavior, driven by strong excitonic effects, offers opportunities for engineering light-matter interactions.
• The findings pave the way for novel photonic devices utilizing MoS2, including metamaterials and light emitters.