Active optical antennas driven by inelastic electron tunneling

Abstract

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.

Directional Control of Light with Nanoantennas

“…This process is named as inelastic electron tunneling. [118,119] Nanoantennas with tunneling junctions can transfer electrical energy directly to the feed point of the nanoantenna. Upon electrical biasing, the tunnel junction in a nanoantenna acts as a light source supporting broadband light emission, and the radiation pattern of the emitted light will be shaped by the nanoantenna.…”

Geometry-induced enhancement factor improvement in covered-gold-nanorod-dimer antennas

“…[19][20][21][22] Bowtie type or rectangular nanoantennas have been synthesized by electron beam microscopy. 6,23,24 As the enhancement factor can reach peak values with arm lengths surpassing the micrometer, an important feature of these structures is that they can be used as addressable electrodes. 25,26 Electrical transport measurements can be coupled with the ability to spectroscopically characterize target molecules at the gap by SERS, either sequentially, 27,28 or simultaneously, as would be our nal goal.…”

Tunable Light Emission by Electrically Excited Plasmonic Antenna

“…Electrically pumped nanoantennas provide a new platform to investigate the interactions between tunneling electrons and plasmon modes. ,− Additionally, study of light emission from nanometer-scale tunnel gaps is beneficial for the development of quantum plasmonics. − For example, plasmon modes have been excited using tunneling nanowires and two-wire nanoantennas. , Via voltage biasing at the ends of the nanoantennas, plasmons are excited using antenna-coupled junctions and provide far-field radiation. The emission spectrum, intensity, and directionality can all be shaped using designed nanoantennas .…”