Influence of chemical treatment on strain and charge doping in vertically stacked monolayer–bilayer MoS2

We report simultaneous Raman scattering and photoluminescence (PL) mapping results to study the strain and doping effects of chemical treatment with bis(trifluoromethane) sulfonimide (TFSI) on the optical phonon, exciton, and trion characteristics of a vertically stacked monolayer–bilayer (1L–2L) MoS2 structure. Correlation analysis between the E ′ and A 1 ′ phonon energies revealed that tensile strain developed in the TFSI-treated MoS2 mainly by the filling of sulfur vacancies: 0.13% and 0.10% for 1L and 2L MoS2, respectively. In addition, TFSI-induced changes in the electron densities evaluated from the Raman correlation analysis were estimated to be − 0.38 × 10 13 cm − 2 and − 1.21 × 10 13 cm − 2 for 1L and 2L MoS2, respectively. The larger p-doping effect in 2L than in 1L MoS2 was attributed to a relatively higher defect density in the 2L region of the pristine MoS2, followed by a subsequent healing of the defects via chemical doping. The TFSI-induced change in electron density estimated from the PL result was in excellent agreement with the Raman correlation analysis. Furthermore, the Raman mapping and PL histogram analyses showed that structural defects in MoS2 could be effectively healed by chemical treatment.