Optically tunable charge carrier injection in monolayer MoS2

We report on excitation laser power-dependent Raman and photoluminescence (PL) measurements on gold nanoparticles-monolayer MoS2 hybrid nanostructures. Excitation of localized surface plasmon resonances in gold nanoparticles and their subsequent non-radiative relaxation inject charge carriers (electrons) into the adjacent monolayer MoS2. Due to the non-centrosymmetric nature of monolayer MoS2, the localized electron doping induces lattice compression via inverse piezoelectric response. The resultant lattice distortion manifests as a shift as well as broadening of A1g(Gamma) and E2g1mml:mfenced close=")" open="("Gamma mml:mfenced MoS2 Raman modes. A splitting of E2g1 mml:mfenced close=")" open="(">Gamma mml:mfenced mode is also observed. The PL spectra reveal power-dependent enhancement of trion feature, which again is a signature of an increasing electron doping. The observed effects are confirmed to be doping related as they are absent in monolayer MoS2 without gold nanoparticles. Our observations reveal that charge carrier injection is effectively controlled by varying the excitation laser power, which may aid in optically tuning physical response of MoS2 hybrid nanostructures and devices.