Monolayer MoS₂ with Controllable and Localized Micro-Scale Domains of Strain enabled by Spatially Varying Nanotopography

The remarkable strain limit of two-dimensional (2D) materials as a result of strong in-plane covalent or ionic bonding provides a straightforward means to tune electronic states by modulating the interatomic distances through mechanical strain^1,2. The high strain sensitivity along with low bending modulus of 2D materials make them promising candidates for eagerly sought-after gradient bandgap materials in which the bandgap spatially varies within the same material ^3–5. These materials would enable absorption and conversion of a broad light spectrum for use in photovoltaics, photocatalysis, and photodetectors^6–8. Meanwhile, two-photon lithography (2PL) is newly capable of lateral resolutions below 200 nm to rapidly fabricate complex three-dimensional structures^9,10. Here, we use 2PL fabricated non-Euclidian nanotopography comprised of periodic undulations with spatially varying height as a patterned substrate for monolayer molybdenum disulfide (MoS₂). The monolayer conformed to the nanotopography locally strains the monolayer with both spatial and magnitudinal control. The conformity of the monolayer is characterized using scanning electron microscopy and atomic force microscopy, and the localized domains of strain in the conformed monolayer are characterized using Raman and photoluminescence spectroscopy. This study serves as a starting point for deterministic straining of 2D materials and development of 2D materials-based broad-spectrum sensing.<br/><br/><b>References</b><br/>1. Sahalianov, I. Y., Radchenko, T. M., Tatarenko, V. A., Cuniberti, G. & Prylutskyy, Y. I. Straintronics in graphene: Extra large electronic band gap induced by tensile and shear strains. <i>J Appl Phys</i> <b>126</b>, (2019).<br/>2. Miao, F., Liang, S. J. & Cheng, B. Straintronics with van der Waals materials. <i>NPJ Quantum Mater</i> <b>6</b>, 2–5 (2021).<br/>3. Kuykendall, T., Ulrich, P., Aloni, S. & Yang, P. Complete composition tunability of InGaN nanowires using a combinatorial approach. <i>Nature Materials 2007 6:12</i> <b>6</b>, 951–956 (2007).<br/>4. Kim, C.-J. <i>et al.</i> On-Nanowire Band-Graded Si:Ge Photodetectors. <i>Advanced Materials</i> <b>23</b>, 1025–1029 (2011).<br/>5. Xiao, Y. <i>et al.</i> Band structure engineering and defect control of Ta3N5 for efficient photoelectrochemical water oxidation. <i>Nature Catalysis 2020 3:11</i> <b>3</b>, 932–940 (2020).<br/>6. Konstantatos, G. & Sargent, E. H. Nanostructured materials for photon detection. <i>Nature Nanotechnology 2010 5:6</i> <b>5</b>, 391–400 (2010).<br/>7. Yan, J., Song, X., Chen, Y. & Zhang, Y. Gradient band gap perovskite films with multiple photoluminescence peaks. <i>Opt Mater (Amst)</i> <b>99</b>, 109513 (2020).<br/>8. Feng, J., Qian, X., Huang, C. W. & Li, J. Strain-engineered artificial atom as a broad-spectrum solar energy funnel. <i>Nat Photonics</i> <b>6</b>, 866–872 (2012).<br/>9. Photonic Professional GT2 from Nanoscribe, GMBH. <i>Nanoscribe GmbH & Co. KG</i> https://www.nanoscribe.com/en/solutions/photonic-professional-gt2 (2021).<br/>10. Vyatskikh, A. <i>et al.</i> Additive manufacturing of 3D nano-architected metals. <i>Nature Communications 2018 9:1</i> <b>9</b>, 1–8 (2018).