Filming Coupled Light and Electrons as They Travel Undercover

The breakthrough is published today in Nature Communications.

The lab of Fabrizio Carbone at EPFL led the project to create a tiny antenna array that would allow plasmons to travel across an interface. The array consisted of an extremely thin membrane of silicon nitride (50 nm thick) covered with an even thinner film of silver (30 nm thick). The scientists then “punched” a series of nano-holes through the surface that would act as the antennas — the plasmon “hotspots”.

The researchers then fired ultrafast laser pulses (light) onto the array to light up the antennas. With a controlled temporal delay, ultrashort electron pulses were then fired across the multilayer stack, to map the plasmons radiated by the antennas at the interface between the silver film and the silicon nitride membrane. Using an ultrafast technique called PINEM, which can “see” surface plasmons, even when they are bound to a buried interface, the scientists were able to actually film the propagation of the guided light and read its spatial profile across the film.

“Trying to see plasmons in these interfaces between layers is a bit like trying to film people in a house from the outside,” explains Fabrizio Carbone. “A regular camera won’t show you anything; but if you use microwave or a similar energy-tracking imaging, you can see right through the walls.”

The current paper paves the way for designing and controlling confined plasmonic fields in multilayered structures, which is key for future optoelectronic devices.

This work included contributions from the University of Glasgow, EPFL’s Interdisciplinary Center for Electron Microscopy, Boston University, the Barcelona Institute of Science and Technology, the Institució Catalana de Recerca i Estudis Avancats, and Trinity College (US). It was funded by the European Research Council (ERC), the Swiss National Science Foundation (NCCR-MUST), Trinity College, the Connecticut Space Grant Consortium, and MINECO (Spain).

Contacts and sources:
Nik Papageorgiou
École Polytechnique Fédérale De Lausanne (EPFL)