Department of Applied Physics, The Hong Kong Polytechnic University , Hong Kong 999077, China.
Department of Physics and Optoelectronics, Key Lab of Advanced Transducers and Intelligent Control System of Ministry of Education, Taiyuan University of Technology , Taiyuan 030024, People's Republic of China.
ACS Nano. 2016 Dec 27;10(12):11105-11114. doi: 10.1021/acsnano.6b05979. Epub 2016 Dec 5.
Single metallic nanostructures supporting strong Fano resonances allow more compact nanophotonics integration and easier geometrical control in practical applications such as enhanced spectroscopy and sensing. In this work, we designed a class of plasmonic split nanodisks that show pronounced Fano resonance comparable to that observed in widely studied plasmonic oligomer clusters. Using our recently developed "sketch and peel" electron-beam lithography, split nanodisks with varied diameter and split length were fabricated over a large area with high uniformity. Transmission spectroscopy measurements demonstrated that the fabricated structures with 15 nm split gap exhibit disk diameter and split length controlled Fano resonances in the near-infrared region, showing excellent agreement with simulation results. Together with the plasmon hybridization theory, in-depth full-wave analyses elucidated that the Fano resonances observed in the split nanodisks were induced by mode interference between the bright antibonding dipole mode of split disks and the subradiant mode supported by the narrow split gap. With the giant near-field enhancement enabled by the intensive Fano resonance at the tiny split gap, strong wavelength-dependent second harmonic generation was observed under near-infrared excitation. Our work demonstrated that single split nanodisks could serve as important building blocks for plasmonic and nanophotonic applications including sensing and nonlinear optics.
单一金属纳米结构支持强的 Fano 共振，允许更紧凑的纳米光子学集成和更容易的几何控制在实际应用中，如增强光谱和传感。在这项工作中，我们设计了一类等离子体分裂纳米盘，显示出明显的 Fano 共振，与广泛研究的等离子体低聚物簇中观察到的共振相当。使用我们最近开发的“草图和剥离”电子束光刻技术，在大面积上以高均匀性制造了具有不同直径和分裂长度的分裂纳米盘。传输光谱测量表明，具有 15nm 分裂间隙的制造结构在近红外区域表现出由圆盘直径和分裂长度控制的 Fano 共振，与模拟结果非常吻合。结合等离子体杂化理论，全波分析深入揭示了在分裂纳米盘中观察到的 Fano 共振是由分裂圆盘的亮反键偶极模式和窄分裂间隙支持的亚辐射模式之间的模式干扰引起的。由于在微小的分裂间隙处存在强烈的 Fano 共振，可实现巨大的近场增强，在近红外激发下观察到强烈的波长依赖性二次谐波产生。我们的工作表明，单一分裂纳米盘可以作为等离子体和纳米光子学应用的重要构建块，包括传感和非线性光学。
