Nonlinear optical materials of atomic thickness--such as non-centrosymmetric 2H transition metal dichalcogenide monolayers--have a second order nonlinear susceptibility (χ(2)) whose intensity can be tuned by strain. However, whether χ(2) is enhanced or reduced by tensile strain is a subject of conflicting reports. Here, we grow high-quality MoSe2 monolayers under controlled biaxial strain created by two different substrates, and study their linear and non-linear optical responses with a combination of experimental and theoretical approaches. A 15-fold overall enhancement in second harmonic generation (SHG) intensity is observed on MoSe2 monolayers grown on SiO2 when compared to its value when on a Si3N4 substrate. A seven-fold enhancement was ascertained to substrate interference, and a factor of two to the enhancement of χ(2) arising from biaxial strain: substrate interference and strain are independent handles to engineer the SHG strength of non-centrosymmetric 2D materials.
@article{arxiv.2407.01339,
title = {Substrate interference and strain in the second harmonic generation from MoSe$_2$ monolayers},
author = {S. Puri and S. Patel and J. L. Cabellos and L. E. Rosas-Hernandez and S. Barraza-Lopez and B. Mendoza and H. Nakamura},
journal= {arXiv preprint arXiv:2407.01339},
year = {2025}
}