Second harmonic microscopy of monolayer MoS2

TL;DR

This paper demonstrates strong second harmonic generation in monolayer MoS2 due to its lack of inversion symmetry, enabling non-invasive optical characterization of atomically thin materials.

Contribution

It provides the first measurement of second harmonic generation in monolayer MoS2 and explores its potential for rapid, non-invasive material analysis.

Findings

Strong SHG in monolayer MoS2 with susceptibility ~1E-7 m/V

SHG signal decreases significantly in multilayer samples

Proof-of-concept SHG microscopy applied to CVD-grown MoS2

Abstract

We show that the lack of inversion symmetry in monolayer MoS2 allows strong optical second harmonic generation. Second harmonic of an 810-nm pulse is generated in a mechanically exfoliated monolayer, with a nonlinear susceptibility on the order of 1E-7 m/V. The susceptibility reduces by a factor of seven in trilayers, and by about two orders of magnitude in even layers. A proof-of-principle second harmonic microscopy measurement is performed on samples grown by chemical vapor deposition, which illustrates potential applications of this effect in fast and non-invasive detection of crystalline orientation, thickness uniformity, layer stacking, and single-crystal domain size of atomically thin films of MoS2 and similar materials.