Imaging and controlling plasmonic interference fields at buried interfaces

October 25, 2016
 

EPFL researchers, who are working to develop potential optical-electronic hybrid computers, have created an ultrafast method that can simultaneously track both light and electrons as they pass through a nanostructured surface.

When both light and electrons come together on a surface, their concentrated motion can move as a wave using the surface geometry. These waves, known as surface plasmons, may be useful in future computing and telecommunications, where data will be transferred across processors by means of light instead of electricity. These processors, in addition to being more energy efficient, could be reduced to the nanoscale in order to make high-resolution sensors as well as nanosized signal processing systems. However, the processors would be developed from assembling different layers of innovative materials and so far there is no a reliable way to track the guided light when it travels across their interfaces.

Researchers at EPFL have now used a new, ultrafast method to track this process. Their research breakthrough is published in Nature Communications. Fabrizio Carbone’s lab at EPFL led the research project to develop a small antenna array to allow plasmons to move across an interface. This array is made of a very thin silicon nitride membrane of 50 nm thickness and is covered with a 30 nm thick silver film.

 
Figure 1. Time-resolved PINEM methodology. (a) Simplified scheme of the time-resolved photon-induced near-field electron microscopy (PINEM) experiments in this work. A photon pump pulse incident on a nanopatterned Ag-on-Si3N4 bilayer structure generates a surface plasmon polariton (SPP) wave propagating along the buried Ag/Si3N4 interface. The near-field of the propagating SPP is subsequently probed through its interaction with a field-of-view electron pulse at a time delay t. Energy-filtered imaging of the resulting electron distribution of transmitted electrons then provides spatially resolved temporal snapshots of the near-field corresponding to the propagating plasmonic wave. (b) Variation of the relative time delay between the optical excitation pulse and the probing electron pulse generates a time-resolved movie of the ultrafast evolution of the buried plasmonic near-field.