AN INTEGRATED ELECTRICAL PLASMON NANOSOURCE – INTELPLAN

Plasmonics, or the use of surface plasmon polaritons instead of electrons or photons to convey information in miniaturized circuits, combines the advantages of photonics—its high speed and large bandwidth—with those of electronics—its extreme miniaturization and integration. But in order for plasmonic circuitry to become a reality, an integrated, electrical, nanoscale source of surface plasmons is necessary. Such a nanosource is proposed in this project.
The basis of the proposed nanosource of surface plasmons is a biased metal-insulator-metal tunnel junction. Such a structure has been long known to emit radiation, but has been neglected because of its low electron-to-plasmon conversion efficiency. The first main goal of this project is to increase this conversion efficiency by over two orders of magnitude through the use of carefully designed plasmonic nano-antennas.
The emission of radiation from biased tunnel junctions is generally attributed to fluctuations of the tunnel current. This interpretation, however, has yet to be unambiguously confirmed by experiment. In order to do so, a correlation measurement of the emitted plasmon intensity and tunnel current fluctuations as a function of time is necessary. Such experiments, proposed in this project, will shed light on the fundamental mechanisms of these surface plasmon nanosources. This is the second main goal of the project.
In order to reach these goals, the following research plan will be followed. First, original nano-antenna designs which specifically target the reduction of losses will be proposed e.g., a gold nanocylinder on a thin gold film. In order to evaluate the efficiency of the nano-antenna, a tunnel junction will be formed between a scanning tunneling microscope tip and the biased antenna. The intensity of the generated surface plasmon polaritons on the gold film will be measured using leakage radiation microscopy and compared to that of a control sample where no antenna is present.
Next, an integrated nano-antenna junction will be fabricated. In this case, a thin insulating film is deposited on top of the cylindrical antenna, followed by a metallic electrode. In other words, the tunnel junction is now integrated in the nano-antenna. In order to test these integrated nano-antenna junctions, the circuit will be completed with the conducting tip of an atomic force microscope. Two different methods will be used to measure the resulting intensity of the surface plasmon radiation: leakage radiation microscopy as in the case of the simple, gold nano-cylinder antenna; and an all-electrical on-chip detection scheme based on a superconducting wire. A third sample consisting of a 1-D array of nano-antenna junctions will be fabricated in order to produce a directional source of surface plasmon polaritons.
In another part of the project, simultaneous plasmon intensity and electrical current noise measurements will be carried out in order to understand the fundamental origin of surface plasmons from biased tunnel junctions, which could lead to improving their efficiency. Two strategies will be used for these correlation experiments. In one case, the measurements will be performed on a 2-D array of nano-antenna junctions, which will have a much improved signal-to-noise ratio as compared to a simple planar junction. The second correlation measurement will use a single nano-antenna junction and on-chip all-electrical plasmon detection.
Significant improvements to the efficiency of surface plasmon nanosources will be the result of this project. In the short term, carefully designed plasmonic nano-antennas which reduce losses will allow a greater than two orders of magnitude increase in the plasmon emission. On a longer timescale, a deeper understanding of the fundamental mechanisms of the plasmon excitation process may lead to further improvements of these plasmon nanosources, e.g., by tailoring the quantum transport statistics via the electromagnetic environment.