Active optical antennas driven by inelastic electron tunneling

In this review, we focus on the experimental demonstration of enhanced emission from single plasmonic tunneling junctions consisting of coupled nano antennas or noble metal tips on metallic substrates in scanning tunneling microscopy. Electromagnetic coupling between resonant plasmonic oscillations of two closely spaced noble metal particles leads to a strongly enhanced optical near field in the gap between. Electron beam lithography or wet chemical synthesis enables accurate control of the shape, aspect ratio, and gap size of the structures, which determines the spectral shape, position, and width of the plasmonic resonances. Many emerging nano-photonic technologies depend on the careful control of such localized resonances, including optical nano antennas for high-sensitivity sensors, nanoscale control of active devices, and improved photovoltaic devices. The results discussed here show how optical enhancement inside the plasmonic cavity can be further increased by a stronger localization via tunneling. Inelastic electron tunneling emission from a plasmonic junction allows for new analytical applications. Furthermore, the reviewed concepts represent the basis for novel ultra-small, fast, optically, and electronically switchable devices and could find applications in high-speed signal processing and optical telecommunications.