We present a novel plasmonic antenna structure, a split-wedge antenna, created by splitting an ultrasharp metallic wedge with a nanogap perpendicular to its apex. The nanogap can tightly confine gap plasmons and boost the local optical field intensity in and around these opposing metallic wedge tips. This three-dimensional split-wedge antenna integrates the key features of nanogaps and sharp tips, i.e., tight field confinement and three-dimensional nanofocusing, respectively, into a single platform. We fabricate split-wedge antennas with gaps that are as small as 1 nm in width at the wafer scale by combining silicon V-grooves with template stripping and atomic layer lithography. Computer simulations show that the field enhancement and confinement are stronger at the tip-gap interface compared to what standalone tips or nanogaps produce, with electric field amplitude enhancement factors exceeding 50 when near-infrared light is focused on the tip-gap geometry. The resulting nanometric hotspot volume is on the order of λ3/106. Experimentally, Raman enhancement factors exceeding 107 are observed from a 2 nm gap split-wedge antenna, demonstrating its potential for sensing and spectroscopy applications.
Bibliographical noteFunding Information:
This research was supported by the Office of Naval Research Young Investigator Program (to X.S.C., N.C.L. and S.-H.O.), the National Science Foundation (CMMI No. 1363334 for D.J.K. and S.-H.O.; ECCS No. 1610333 for S.-H.O.; CAREER Award No. 1552642 for N.C.L.; NSF Graduate Research Fellowship for D.J.K.), Seagate Technology (MINT grant for S.-H.O.), and the MnDrive Initiative from the State of Minnesota (to D.J.K. and S.-H.O.). X.S.C. acknowledges support from the 3M Science and Technology Fellowship and the University of Minnesota Doctoral Dissertation Fellowship.
- Optical antenna
- atomic layer deposition
- atomic layer lithography
- gap plasmon
- surface-enhanced Raman scattering (SERS)
- template stripping