Monolayer transition metal dichalcogenides (TMDs) possess large second-order nonlinear responses due to the broken inversion symmetry, which can extend their intriguing applications in nonlinear nanophotonics and optoelectronics. However, the atomic thickness of monolayer TMDs severely decreases the interaction length with free light with respect to bulk materials, leading to rather low second-harmonic generation (SHG) conversion efficiency. Here, we demonstrate a hybrid structure consisting of a monolayer MoS 2 on a suspended perforated silver film, on which the SHG signal emitted from the monolayer MoS 2 is enhanced by more than three orders of magnitude at room temperature. The pronounced SHG enhancement is attributed to the distinct electric field amplification nearby the nanoholes, which is induced by the symmetric surface plasmon polaritons (SPPs) existing in the ultrathin suspended silver grating. Our results reported here may establish the substrate-free engineering of nonlinear optical effects via plasmonic nanostructures on demand.

中文翻译：

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通过等离子体共振增强悬浮金属纳米结构上单层二硫化钼的二次谐波产生

由于破坏了反转对称性，单层过渡金属二硫属化物 (TMD) 具有较大的二阶非线性响应，这可以扩展其在非线性纳米光子学和光电子学中的有趣应用。然而，单层 TMD 的原子厚度严重降低了与自由光相对于体材料的相互作用长度，导致二次谐波产生 (SHG) 转换效率相当低。在这里，我们展示了由悬浮穿孔银膜上的单层 MoS 2 组成的混合结构，在室温下，单层 MoS 2 发出的 SHG 信号增强了三个数量级以上。显着的 SHG 增强归因于纳米孔附近明显的电场放大，这是由存在于超薄悬浮银光栅中的对称表面等离子体激元（SPP）引起的。我们在此报告的结果可能会根据需要通过等离子体纳米结构建立非线性光学效应的无基底工程。