Dielectric properties and exciton tunability of two-dimensional $WS_{2}$ in van der Waals bilayers.

Peci E., Magnozzi M., Ramò L., Ferrera M., Convertino D., Pace S., Orlandini G., Sharma A., Milekhin I., Salvan G., Coletti C., Zahn D.R.T., Bisio F., Canepa M.
  Lunedì 12/09   14:00 - 19:00   Aula D - Marianna Ciccone   II - Fisica della materia   Presentazione
The opto-electronic properties of two-dimensional tungsten disulfide can be manipulated via its inclusion in tailored van der Waals (vdW) multilayer heterostacks. We present a spectroscopic ellipsometry (SE) investigation of several vdW heterostacks featuring $WS_{2}$ in monolayer configuration, $2H$ and $3R$ bilayer stacking, and $WS_{2}/MoS_{2}$ vertical heterostructure. Exploiting a parametric optical model, a Kramers-Kronig consistent dielectric function is extracted for each system, which allows to precisely identify the A, B and C excitons, to highlight their energy shifts (tens of meV) as a function of the different stacking configuration and to rationalize them based on different dielectric environments and interlayer interaction. The stacking-dependent energy shifts of the excitonic peaks observed through SE are also confirmed by transmittance spectroscopy. An exciton tunability up to $40 {meV}$ is thus demonstrated.