Strain-modulated excitonic gaps in mono- and bi-layer MoSe<inf>2</inf>

Abstract

© 2016 Chinese Physical Society and IOP Publishing Ltd. Photoluminescence (PL) and Raman spectra under uniaxial strain were measured in mono- and bi-layer MoSe 2 to comparatively investigate the evolution of excitonic gaps and Raman phonons with strain. We observed that the strain dependence of excitonic gaps shows a nearly linear behavior in both flakes. One percent of strain increase gives a reduction of ∼ 42 meV (∼ 35 meV) in A-exciton gap in monolayer (bilayer) MoSe 2 . The PL width remains little changed in monolayer MoSe 2 while it increases rapidly with strain in the bilayer case. We have made detailed discussions on the observed strain-modulated results and compared the difference between monolayer and bilayer cases. The hybridization between 4d orbits of Mo and 4p orbits of Se, which is controlled by the Se-Mo-Se bond angle under strain, can be employed to consistently explain the observations. The study may shed light into exciton physics in few-layer MoSe 2 and provides a basis for their applications.