Giant Enhancement of Second Harmonic Generation From WS2 Monolayer Driven by Nanocavity‐Induced Strain

Abstract

Improving the optical nonlinearity of monolayer transition metal dichalcogenides is not only interesting for fundamental research but also highly desirable for practical application. Here, the realization of greatly enhanced second harmonic generation (SHG) is reported in a non‐uniformly strained WS2 monolayer induced by a Si/Au nanocavity. Si/Au nanocavities supporting optical resonances are created at different wavelengths by placing silicon (Si) nanoparticles with different diameters on a thin gold (Au) film, and introduce spatially localized and non‐uniform strain in a WS2 monolayer by transferring the WS2 monolayer onto such Si/Au nanocavities. A large enhancement is observed in the photoluminescence intensity of the strained WS2 monolayer. More interestingly, it is found that the SHG from the strained WS2 monolayer is significantly enhanced by a factor as large as ≈9649. This study reveals that the SHG enhancement depends strongly on the magnitude of the strain and exhibits high anisotropy. Moreover, this study demonstrates that the wavelength‐dependent SHG enhancement can be manipulated by exploiting the optical resonance supported by the Si/Au nanocavity. These findings suggest the potential applications of non‐uniform strain induced by dielectric‐metal nanocavities in the development of highly efficient nonlinear optical devices and nanoscaled quantum photonic devices.