Photoluminescence enhancement of monolayer MoS2 using plasmonic gallium nanoparticles

2D monolayer molybdenum disulphide (MoS2) has been the focus of intense research due to its direct bandgap compared with the indirect bandgap of its bulk counterpart; however its photoluminescence (PL) intensity is limited due to its low absorption efficiency. Herein, we use gallium hemispherical nanoparticles (Ga NPs) deposited by thermal evaporation on top of chemical vapour deposited MoS2 monolayers in order to enhance its luminescence. The influence of the NP radius and the laser wavelength is reported in PL and Raman experiments. In addition, the physics behind the PL enhancement factor is investigated. The results indicate that the prominent enhancement is caused by the localized surface plasmon resonance of the Ga NPs induced by a charge transfer phenomenon. This work sheds light on the use of alternative metals, besides silver and gold, for the improvement of MoS2 luminescence.