Exciton-dominated Dielectric Function of Atomically Thin MoS2 Films

Yiling Yu, Yifei Yu, Yongqing Cai, Wei Li, Alper Gurarslan, Hartwin Peelaers, David E. Aspnes, Chris G. Van De Walle, Nhan V. Nguyen, Yong Wei Zhang, Linyou Cao*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

147 Citations (Scopus)


We systematically measure the dielectric function of atomically thin MoS2 films with different layer numbers and demonstrate that excitonic effects play a dominant role in the dielectric function when the films are less than 5-7 layers thick. The dielectric function shows an anomalous dependence on the layer number. It decreases with the layer number increasing when the films are less than 5-7 layers thick but turns to increase with the layer number for thicker films. We show that this is because the excitonic effect is very strong in the thin MoS2 films and its contribution to the dielectric function may dominate over the contribution of the band structure. We also extract the value of layer-dependent exciton binding energy and Bohr radius in the films by fitting the experimental results with an intuitive model. The dominance of excitonic effects is in stark contrast with what reported at conventional materials whose dielectric functions are usually dictated by band structures. The knowledge of the dielectric function may enable capabilities to engineer the light-matter interactions of atomically thin MoS 2 films for the development of novel photonic devices, such as metamaterials, waveguides, light absorbers, and light emitters.

Original languageEnglish
Article number16996
JournalScientific Reports
Publication statusPublished - 24 Nov 2015
Externally publishedYes


This work was supported by a Young Investigator Award from the Army Research Office (W911NF-13-1-0201). Y.C. and Y.Z. gratefully acknowledge the use of computing resources at the A*STAR Computational Resource Centre, Singapore. H.P. and C.G.V.d.W. were supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award DE-FG02-07ER46434.

FundersFunder number
U.S. Department of Energy
Army Research OfficeW911NF-13-1-0201
Office of Science
Basic Energy SciencesDE-FG02-07ER46434


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