We combine atomic layer lithography and glancing-angle ion polishing to create wafer-scale metamaterials composed of dense arrays of ultrasmall coaxial nanocavities in gold films. This new fabrication scheme makes it possible to shrink the diameter and increase the packing density of 2 nm-gap coaxial resonators, an extreme subwavelength structure first manufactured via atomic layer lithography, both by a factor of 100 with respect to previous studies. We demonstrate that the nonpropagating zeroth-order Fabry-Pérot mode, which possesses slow light-like properties at the cutoff resonance, traps infrared light inside 2 nm gaps (gap volume ∼ λ3/106). Notably, the annular gaps cover only 3% or less of the metal surface, while open-area normalized transmission is as high as 1700% at the epsilon-near-zero (ENZ) condition. The resulting energy accumulation alongside extraordinary optical transmission can benefit applications in nonlinear optics, optical trapping, and surface-enhanced spectroscopies. Furthermore, because the resonance wavelength is independent of the cavity length and dramatically red shifts as the gap size is reduced, large-area arrays can be constructed with λresonance period, making this fabrication method ideal for manufacturing resonant metamaterials.
Bibliographical noteFunding Information:
This research was supported by the Office of Naval Research Young Investigator Program (D.Y. and S.-H.O.), Seagate Technology (J.S. and S.-H.O.), and the NIH Biotechnology Training Grant (D.A.M.). N.C.N. and J.P. acknowledge support from the Air Force Office of Scientific Research (AFOSR Grants FA9550-12-1-0357 and FA9550-11-1-0141). L.M.-M. acknowledges support from the Spanish Ministry of Economy and Competitiveness (MAT2014-53432- C5-1-R). T.W.E. acknowledges support from the Agence National de la Recherche (ANR) Equipex Union (ANR-10-EQPX-52-01), the Labex NIE projects (ANR-11-LABX-0058 NIE), and the Investissement d''Avenir program (ANR-10-IDEX- 0002-02). Device fabrication was performed at the Minnesota Nano Center (MNC) at the University of Minnesota, which receives partial support from the NSF through the National Nanotechnology Coordinated Infrastructure (NNCI). Electron microscopy and FTIR measurements were performed at the Characterization Facility at the University of Minnesota, which has received capital equipment from the NSF MRSEC. The authors thank Xiaoshu Chen and Fernando Reitich for helpful comments.
- Coaxial nanohole
- atomic layer lithography
- epsilon-near-zero metamaterial
- extraordinary optical transmission
- glancing-angle ion milling
- slow light