Modification of Optical Properties in Monolayer WS₂ on Dielectric Substrates by Coulomb Engineering

The optical properties of monolayer materials can be indirectly tuned by the dielectric properties of surrounding materials. Although proof-of-concepts for this so-called Coulomb engineering have already been shown, the verification of the proposed effect for a wide range of different dielectric substrates is still missing. By employing reflectance and photoluminescence spectroscopy, we study the effect of dielectric screening on the optical properties of a monolayer WS₂ fabricated on five substrates with different dielectric constants. A systematic but moderate energy shift of the A-exciton resonance up to 40 meV is observed as the dielectric constant of the substrate increases. We consistently explain the shift in terms of the electron-hole Coulomb interaction due to dielectric screening. A theoretical calculation suggests that a significant modification of the band gap and exciton binding energies takes place but results only in a moderate shift of the exciton resonance energy because the influences of band gap and exciton energy shifts cancel each other to a large degree. Our results demonstrate the systematic tuning of optical properties by controlling the effective dielectric constant via the substrate, which is an important approach for the development of artificial materials.