Because indi­vidual atoms or molecules are 100 to 1000 times smaller than the wavelength of visible light, it is notoriously difficult to collect infor­mation about their dynamics, especially when they are embedded within larger structures. In an effort to circumvent this limitation, researchers are engi­neering metallic nano-antennas that concen­trate light into a tiny volume to drama­tically enhance any signal coming from the same nanoscale region. Nano-antennas are the backbone of nanoplas­monics, a field that is profoundly impacting biosensing, photo­chemistry, solar energy harvesting, and photonics.

Now, researchers at Ecole Poly­technique Fédérale de Lausanne EPFL led by Christophe Galland at the School of Basic Sciences have discovered that when shining green laser light on a gold nano-antenna, its intensity is locally enhanced to a point that it knocks gold atoms out of their equi­librium positions, all the time main­taining the integrity of the overall structure. The gold nano-antenna also amplifies the very faint 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 signatures of atoms undergoing rearrange­ments. “Such atomic scale phenomena would be difficult to observe in situ, even using highly sophis­ticated electron or X-ray micro­scopes, because the clusters of gold atoms emitting the flashes of light are buried inside a complex environ­ment among billions of other atoms,” says Galland.

The unexpected findings raise new questions about the exact micro­scopic mechanisms by which a weak conti­nuous green light can put some gold atoms into motion. “Ans­wering them will be key to bringing optical nano-antennas from the lab into the world of appli­cations – and we are working on it,” says Wen Chen. (Source: EPFL)

Reference: W. Chen et al.: Intrinsic luminescence blinking from plasmonic nanojunctions, Nat. Commun. 12, 2731 (2021); DOI: 10.1038/s41467-021-22679-y

Link: Laboratory of Quantum and Nano-Optics, Ecole Polytechnique Fédérale de Lausanne EPFL, Lausanne, Switzerland