Nanogaps Between Metals Create Light Ten Thousand Times Brighter Than Expected

Nanogaps between plasmonic electrodes produced 10,000 times more light than expected. Hot electrons were created by electrons driven to tunnel between gold electrodes, their recombination with holes emitted bright light, and the greater the input voltage, the brighter the light.

This could be useful for applications in optoelectronics, quantum optics and photocatalysis.

The effect depends upon the metal’s plasmons, ripples of energy that flow across its surface.

Researchers formed several metals into microscopic, bow tie-shaped electrodes with nanogaps, a test bed developed by the lab that lets them perform simultaneous electron transport and optical spectroscopy. Gold was the best performer among electrodes they tried, including compounds with plasmon-damping chromium and palladium chosen to help define the plasmons’ part in the phenomenon.

“If the plasmons’ only role is to help couple the light out, then the difference between working with gold and something like palladium might be a factor of 20 or 50,” Natelson said. “The fact that it’s a factor of 10,000 tells you that something different is going on.”

The reason appears to be that plasmons decay “almost immediately” into hot electrons and holes, he said. “That continuous churning, using current to kick the material into generating more electrons and holes, gives us this steady-state hot distribution of carriers, and we’ve been able to maintain it for minutes at a time,” Natelson said.

Nanoletters – Electrically Driven Hot-Carrier Generation and Above-Threshold Light Emission in Plasmonic Tunnel Junctions


Above-threshold light emission from plasmonic tunnel junctions, when emitted photons have energies significantly higher than the energy scale of incident electrons, has attracted much recent interest in nano-optics, while the underlying physics remains elusive. We examine above-threshold light emission in electromigrated tunnel junctions. Our measurements over a large ensemble of devices demonstrate a giant (∼104) material-dependent photon yield (emitted photons per incident electrons). This dramatic effect cannot be explained only by the radiative field enhancement due to localized plasmons in the tunneling gap. Emission is well described by a Boltzmann spectrum with an effective temperature exceeding 2000 K, coupled to a plasmon-modified photonic density of states. The effective temperature is approximately linear in the applied bias, consistent with a suggested theoretical model describing hot-carrier dynamics driven by nonradiative decay of electrically excited localized plasmons. Electrically generated hot carriers and nontraditional light emission could open avenues for active photochemistry, optoelectronics, and quantum optics.

SOURCES – Rice University, Nanoletters
Written By Brian Wang,

19 thoughts on “Nanogaps Between Metals Create Light Ten Thousand Times Brighter Than Expected”

  1. Gold is quite high now. But given the enormous deficits, and the prospect of more no matter who wins in November, it could go higher.

  2. Ah, so it’s not going to be the next LED.

    Always nice to hear from the author, by the way.

  3. Author here. You’re right to worry about electromigration – that’s actually how we make the little tunneling gaps in the first place, by electromigrating a metal constriction until a break forms. In practice, if the substrate is kept at cryogenic temperatures and the junction has survived the relatively high biases (~ 1 V), minutes under sustained current are possible. Stability is definitely an issue, since tunneling conduction is exponentially sensitive to atomic positions (the basis for STM).

  4. There might be some minor erosion, but for the most part, the gold atoms should stay in place. The only things that are moving are electrons and light. (edit: The “holes” here are just missing electrons.)

  5. Upon further thought, seems like this may make a powerful light from electricity that will then efficiently split H2O, more efficiently than the electricity would have.?? Rather than somehow splitting the H2O in one of these cavities with light input.

  6. Can the reverse phenomenon somehow work? Can light be very efficiently converted into electric current via this method? Might require some kind of lenses or solar concentrators, perhaps.

  7. So, how long does the feature last under sustained current? “Hot” carriers probably have enough energy to occasionally displace atoms, you might see sputtering, diffusion, electromigration.

  8. Nano says it all. These are very small things…even if trillions of them were made.
    Just looking at gold independent of this? I think it is a bit high. There are cheap stocks. Restaurants are cheap, airlines, hotels, amusement stuff like Sea World (I bought stock in all these)…too many opportunities to hunker down with gold in my opinion. Mortgage companies and Cruise lines I am more concerned they could go belly up or just have so few assets that they are basically back to square one, and not able to capitalize if and when things get back to normal.

  9. Please explain. This looks like electrons to light, not light to electrons, but, all things are reversible.

  10. Sooo . . . is it time to buy gold again?

    Does this in any way use up or diminish the gold? Does it render any part of the gold into an unrecoverable, or nearly unrecoverable state?

    How valuable is this effect likely to be when put to practical purposes?

    Other than for its intrinsic economic value and as a potential hedge against inflation, is it time to buy gold again?

  11. It’s exciting when unexpected results are observed. Please keep us updated with future research and development on this.

  12. It’s interesting — photocatalysis is apparently good for electrolysis of water, which is step 1 for ISRU.

  13. Egads… I really need to build that lab in my garage… But on a side note, I really love the look on the neophyte’s face when explaining hole flow and electron flow.

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