Sudden outcomes from metallic nano-antennas that focus gentle

Plasmonic nano-antennas manufactured at EPFL: Gold nanoparticles are deposited on a gold film covered with a molecular layer. The light emission from defects in the vicinity of the film surface is strongly amplified by the antenna effect and enables their detection. Photo credit: Nicolas Antille,

Since individual atoms or molecules are 100 to 1000 times smaller than the wavelength of visible light, it is known to be difficult to collect information about their dynamics, especially when they are embedded in larger structures.

To get around this limitation, the researchers are developing metallic nano-antennas that concentrate light into a tiny volume to dramatically improve any signal from the same nanoscale region. Nano-antennas are the backbone of nanoplasmonics, an area that has a strong influence on biosensors, photochemistry, the harvest of solar energy, and photonics.

Researchers at EPFL, led by Professor Christophe Galland from the School of Basic Sciences, have now found that the intensity of green laser light on a gold nano-antenna is locally increased so much that it “pushes” gold atoms out of their equilibrium positions, whereby the integrity the overall structure is constantly preserved. The gold nano-antenna also amplifies the very weak light scattered by the newly formed atomic defects, making it visible to the naked eye.

This nanoscale dance of atoms can thus be observed as orange and red flashes of fluorescence, which are the signatures of atoms that are subject to rearrangements. “Such phenomena at the atomic level would be difficult to observe in situ, even with highly developed electron or X-ray microscopes, since the clusters of gold atoms that emit flashes of light are buried under billions of other atoms in a complex environment,” says Galland.

The unexpected results raise new questions about the exact microscopic mechanisms by which a weak, continuous green light can set some gold atoms in motion. “Your answer will be the key to bringing optical nano-antennas from the laboratory to the world of applications – and we are working on it,” says Wen Chen, the first author of the study.

Reference: “Intrinsic luminescence that flashes through plasmonic nano-transitions” by Wen Chen, Philippe Roelli, Aqeel Ahmed, Sachin Verlekar, Huatian Hu, Karla Banjac, Magalí Lingenfelder, Tobias J. Kippenberg, Giulia Tagliabue and Christophe Galland, May 21, 2021, Nature Communications.
DOI: 10.1038 / s41467-021-22679-y

Funding: Swiss National Science Foundation (SNSF), EU Horizon 2020, Max Planck EPFL Center for Molecular Nanosciences and Technology

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