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Karl Enzo Kloß presents

 Influence of the dielectric substrate on the electronic band structure in a monolayer of TMDC

Thursday,  June 30th 2022 at 14:00

Room D420 – Institut Néel

Link visio : (to come)

The defence will be in English.




In the family of 2D materials, transition metal dichalcogenide monolayers, and in particular, MoS2, MoSe2, WS2, WSe2, are semiconductors with exceptional optoelectronic properties. These properties are due to their nanometric thickness and the resulting consequences on their band structure. This influence offers a unique opportunity to control the optoelectronic properties of these materials by simply modifying their dielectric environment. In this work, we experimentally examine this influence by exposing a WSe2 monolayer to different substrates. We use mechanical exfoliation and a stamping technique to produce different samples of WSe2 monolayers on substrates of different dielectric constants. Using a photoemission technique called k-space Photoelectron Emission Microscopy (kPEEM), we measure the electronic band structure of a WSe2 monolayer deposited on these different substrates. A numerical analysis work allows us to quantitatively extract the essential characteristics of the band structure. We indeed note that these characteristics depend on the substrate, via a dielectric screening mechanism induced by the substrate on the electronic states of the monolayer located at a few nanometer distance. We note in particular that we can significantly modify the energies of the valence band in K and in, which play a key role in the optoelectronic properties of the material. We discuss this effect in light of recent theoretical work and rule out other mechanisms that might be responsible for altering the band structure, such as mechanical strain and charge transfer.