title: Pronounced Fano Resonance in Single Gold Split Nanodisks with 15 nm Split Gaps for Intensive Second Harmonic Generation.
abstract: 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.
authors.forename: Shi
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Department of Applied Physics, The Hong Kong Polytechnic University , Hong Kong 999077, China.
authors.forename: Guang-Can
authors.initials: GC
authors.lastname: Li
authors.forename: Yiqin
authors.identifier: 0000-0003-4635-0666
authors.initials: Y
authors.lastname: Chen
authors.forename: Xupeng
authors.initials: X
authors.lastname: Zhu
authors.affiliation: 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.
authors.forename: Shao-Ding
authors.initials: SD
authors.lastname: Liu
authors.affiliation: Department of Applied Physics, The Hong Kong Polytechnic University , Hong Kong 999077, China.
authors.forename: Dang Yuan
authors.initials: DY
authors.lastname: Lei
authors.forename: Huigao
authors.identifier: 0000-0002-7016-6343
authors.initials: H
authors.lastname: Duan
keywords: Fano resonance; second harmonic generation; sketch and peel lithography; split disks; surface plasmon