Substrate Interference and Strain in the Second-Harmonic Generation from MoSe 2 Monolayers

• Published in: Nano letters
• Main Authors: Puri, Sudeep, Patel, Sneha, Cabellos, Jose Luis, Rosas-Hernandez, Luis Enrique, Reynolds, Katlin, Churchill, Hugh O. H., Barraza-Lopez, Salvador, Mendoza, Bernardo S., Nakamura, Hiroyuki
• Format: Journal Article
• Language: English
• Published: United States 02.10.2024
• Subjects: biaxial strain; second-harmonic generation; 2D materials
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.4c03880

Nonlinear optical materials of atomic thickness, such as non-centrosymmetric 2H transition metal dichalcogenide monolayers, have a second-order nonlinear susceptibility (χ ) whose intensity can be tuned by strain. However, whether χ is enhanced or reduced by tensile strain is a subject of conflicting reports. Here, we grow high-quality MoSe monolayers under controlled biaxial strain created by two different substrates and study their linear and nonlinear optical responses with a combination of experimental and theoretical approaches. Up to a 15-fold overall enhancement in second-harmonic generation (SHG) intensity is observed from MoSe monolayers grown on SiO when compared to its value on a Si N substrate. By considering an interference contribution from different dielectrics and their thicknesses, a factor of 2 enhancement of χ was attributed to the biaxial strain: substrate interference and strain are independent handles to engineer the SHG strength of non-centrosymmetric 2D materials.