Enhanced second harmonic generation in hybrid MoS2/Au/MoS2 and MoS2/SiO2/MoS2 Langmuir-Blodgett films

Abstract

Transition metal dichalcogenides have gained much attention due to their semiconducting properties, enabling a wealth of applications that integrate these 2D materials. Optical properties such as luminescence and nonlinear optical properties are of particular interest for photonic applications despite the small surface of the individual exfoliated flakes or the inherent difficulty to mechanically transfer flakes grown by CVD onto a given substrate. Herein, we investigate the Langmuir-Blodgett transfer of exfoliated MoS₂ flakes deposited onto glass coverslips. Intercalation of Au and SiO₂ nanoparticles between 2 layers of MoS₂ was conducted using successive LB deposition, enabling the formation of heterostructures films with conductor and dielectric materials. The properties of these films were investigated using Raman spectroscopy and second harmonic generation (SHG) microscopy. The multilayers films are transferred on ∼ cm² surface area with good coverage but with uncontrolled crystalline orientation of the MoS₂ flakes. Raman enhancement of MoS₂ was evidenced when Au nanoparticles are intercalated between two layers of MoS₂. Polarized SHG microscopy shows a transition from quadrupolar response of the MoS₂ flake driven by their D_3h symmetry to a dipolar polarized response driven by the Au nanoparticles.