Effect of lithium doping on the optical properties of monolayer MoS2

The effect of lithium atoms' evaporation on the surface of monolayer MoS2 grown on SiO2/Si substrate is studied using ultrahigh vacuum (similar to 10(-11) mbar) Raman and circularly polarized photoluminescence spectroscopies, at low lithium coverage (up to similar to 0.17 monolayer). With increasing Li doping, the dominant E-2g(1) and A(1g) Raman modes of MoS2 shift in energy and broaden. Additionally, non zone-center phonon modes become Raman active. This regards, in particular, to double resonance Raman scattering processes, involving longitudinal acoustic phonon modes at the M and K points of the Brillouin zone of MoS2 and defects. It is also accompanied by a significant decrease in the overall intensity and the degree of circular polarization of the photoluminescence spectrum. The observed changes in the optical spectra are understood as a result of electron doping by lithium atoms and disorder-activated intervalley scattering of electrons and holes in the electronic band structure of monolayer MoS2. Published by AIP Publishing.