Strain-Induced Second Harmonic Generation Enhancement in Monolayer MoS₂ Flakes Edge

Man-Hong Lai^1*, Wei-Liang Chen¹, Chao-Yuan Lo¹, Jia-Ru Yu², Po-Wen Tang², Chi Chen², Yu-Ming Chang¹

¹Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
²Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan

* Presenter:Man-Hong Lai, email:manhonglai@ntu.edu.tw

In this work, we report the strain-induced SHG enhancement at the edge of the monolayer MoS₂ flakes. The SHG intensity images show an enhanced SHG intensity at the flake edge with cubic-power dependence. The AFM analysis of the MoS₂ flake edge with enhanced SHG indeed detected a topographic height change as compared to the center region. Micro-Raman spectroscopy analysis shows a blue-shift in A_1g phonon mode at the flake edge. This edge enhanced-SHG may be attributed to the intrinsic strain effect induced during the CVD growth condition, which modulates the nonlinear susceptibility. The micro-Raman spectroscopy implies that the flake edge has a compressed and stiffened structure in an out-of-plane direction. This finding brings out the awareness of the residual strain effect on 2D TMD device performance, and the adequate characterization of strained structure by SHG intensity mapping.

Keywords: Second harmonic generation, Transition metal dichalcogenides, Thermal effects, Surface strains, Nonlinear optical properties