Publishing their results in Nature Communications with a paper titled "Towards femtosecond on-chip electronics based on plasmonic hot electron nano-emitters", the researchers explain how they were able to leverage 1.5µm near infrared 270THz optical pulses from a telecom-compatible Er:fiber laser to "pump" and excite nanoscale asymmetric plasmonic antennas, yielding a field emission of ballistic hot electrons across the junctions, akin to electronic pulses in the THz range.
These pulses then propagated as electronic signals in millimetre-scale strip lines arranged on the chip (gold electrodes laid on sapphire). In effect, the asymmetric nanoscale metal junctions, each consisting of a triangular-shaped emitter electrode and a plane collector electrode separated by a 90nm vacuum gap, behave like ultra-fast photo-switches that operate a plasmonically enhanced, multiphoton absorption, observed the researchers. This multiphoton absorption triggers the non-linear photoemission of electrons, from the emitter to the collector, generating THz current pulses flowing along the metal strips.
The authors anticipate that such asymmetric plasmonic antennas could be integrated in wafer-scale THz circuits for femtosecond on-chip clock and synchronization dynamics up to 10THz.
The experiments were funded by the European Research Council (ERC) as part of the "NanoREAL" project and the DFG Cluster of Excellence "Nanosystems Initiative Munich" (NIM).
Technical University of Munich - www.tum.de