We report spatially resolved Raman scattering results of polycrystalline monolayer graphene films to study the effects of defects, strains, and strain fluctuations on the electrical performance of graphene. Two-dimensional Raman images of the integrated intensities of the G and D peaks (I G and I D) were used to identify the graphene domain boundaries. The domain boundaries were also identified using Raman images of I D/I G and I 2D/I G ratios and 2D spectral widths. Interestingly, the I D maps showed that the defects within individual domains significantly increased for the graphene with large domain size. The correlation analysis between the G and 2D peak energies showed that biaxial tensile strain was more developed in the graphene with large domain size than in the graphene with small domain size. Furthermore, spatial variations in the spectral widths of the 2D peaks over the graphene layer showed that strain fluctuations were more pronounced in the graphene with large domain size. It was observed that the mobility (sheet resistance) was decreased (increased) for the graphene with large domain size. The degradation of the electrical transport properties of the graphene with large domain size is mainly due to the defects, tensile strains, and local strain fluctuations within the individual domains.

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 A1′ 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 −0.38×1013 cm−2 and −1.21×1013 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.

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