title: Split-Wedge Antennas with Sub-5 nm Gaps for Plasmonic Nanofocusing.
abstract: 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 107are observed from a 2 nm gap split-wedge antenna, demonstrating its potential for sensing and spectroscopy applications.
authors.affiliation: Department of Electrical and Computer Engineering, University of Minnesota , Minneapolis, Minnesota 55455, United States.
authors.forename: Xiaoshu
authors.initials: X
authors.lastname: Chen
authors.affiliation: Department of Electrical and Computer Engineering, University of Minnesota , Minneapolis, Minnesota 55455, United States.|Physics Department, Bethel University , Saint Paul, Minnesota 55112, United States.
authors.forename: Nathan C
authors.initials: NC
authors.lastname: Lindquist
authors.affiliation: Department of Electrical and Computer Engineering, University of Minnesota , Minneapolis, Minnesota 55455, United States.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Klemme
authors.affiliation: Chemical and Biological Engineering, University of Colorado , Boulder, Colorado 80303, United States.
authors.forename: Prashant
authors.initials: P
authors.lastname: Nagpal
authors.affiliation: Optical Materials Engineering Laboratory, ETH Zurich , 8092 Zurich, Switzerland.
authors.forename: David J
authors.initials: DJ
authors.lastname: Norris
authors.affiliation: Department of Electrical and Computer Engineering, University of Minnesota , Minneapolis, Minnesota 55455, United States.
authors.forename: Sang-Hyun
authors.initials: SH
authors.lastname: Oh
keywords: Optical antenna; atomic layer deposition; atomic layer lithography; gap plasmon; surface-enhanced Raman scattering (SERS); template stripping