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.
@article{arxiv.1302.3935,
title = {Second harmonic microscopy of monolayer MoS2},
author = {Nardeep Kumar and Sina Najmaei and Qiannan Cui and Frank Ceballos and Pulickel M. Ajayan and Jun Lou and Hui Zhao},
journal= {arXiv preprint arXiv:1302.3935},
year = {2015}
}