Surface plasmon polariton excitation in exfoliated MoS₂ flakes on Au nanogratings

We prepared MoS₂ flakes on Au nanogratings to investigate how the surface plasmon polariton (SPP) excitation can affect physical properties of MoS₂. SPP – the propagating electromagnetic and charge wave at metal/dielectric interface – can be excited using grating structures by overcoming the momentum mismatch between the impinging photons and the SPPs. The MoS₂ flakes were exfoliated from its bulk and transferred on the Au nanogratings (period: 500 nm) fabricated by electron beam lithography. The number of MoS₂ layers was identified using micro-Raman and atomic force microscopy measurements. Finite-difference time-domain simulations showed clear signature of the SPP excitation in the electric field intensity distributions and optical reflection spectra of the Au nanogratings. The work function of the MoS₂ flakes was measured using Kelvin probe force microscopy, and its variation in dark and light was studied to understand the interaction between the SPPs at the MoS₂/Au interface and charge carriers in the MoS₂ flakes. This study can help us to develop new kinds of 2D transition metal dichalcogenide semiconductor-based plasmonic devices.