Nano Lett. 13, 2846–2850 (2013)

Plasmons are conventionally excited by illuminating metal–dielectric interfaces with light. However, electronic excitation is also possible, albeit with some caveats. For example, the tunnel current between the tip of a scanning tunnelling microscope and a surface can drive plasma and surface plasmon oscillations. Now, Theresa Lutz and colleagues from Germany, France and Switzerland have used a scanning tunnelling microscope to study tris-(phenylpyridine)-iridium complexes on a C60 monolayer and found that such systems can control excitation of plasmons on a silver substrate. They discovered that single molecules in a tunnel junction act as gates for the electrical excitation of optical plasmons under a ∼1–2 V bias. They explain that the intensity and spectral distribution (that is, the colour) of the generated plasmons are directly related to the spatial shape and energy of the orbital closest to the Fermi energy. The team hopes that the idea may ultimately allow molecular tunnel junctions to act as electrically controlled plasmon sources.