Relaying of the local enhanced electric-field using stacked gold bowtie nanoantennas

We demonstrate the possibility of designing plasmonic structures that extend, and even further concentrate the field enhancement in the feed-gap region of single-layer Au bowtie nanoantennas (BNAs) hundreds of nanometers away from the initial metal-dielectric interface. The design is based on a stack of Au BNAs with progressively reduced gap distances sandwiched by thin dielectric layers. We find that this stacked BNA geometry also behaves as a near-field focusing lens of nanometer focal length. By merely controlling the number of BNAs in a stack and thickness of the accompanying dielectric layers, we show that the usual fast-damping field enhancement right above a 50 nm thick base BNA can be relayed and maintained at >10⁴ over a distance of at least up to 200 nm above the base BNA surface. Our novel plasmonic structures offer an approach to design plasmonic nanostructures for applications in metamaterial engineering, SERS, and nonlinear optics.