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Hot electrons generate light in chips

A metamaterial developed by researchers at King’s College London uses quantum effects to turn electrons flowing through a circuit into ‘hot electrons’ and light in a highly controlled manner. According to the team, this has potential application in optoelectronics and sensing.

The nanomaterial takes advantage of electron tunnelling to produce streams of particles which can have important applications, when properly controlled.

Researcher Dr Pan Wang said: “This one tiny device offers several amazing applications: plasmon excitation, light generation and chemical reaction activation. And all this is achieved by a small, easy to produce material which only requires a small voltage to function.”

A voltage applied across the device causes electrons to flow from one material (eutectic gallium indium) to another (gold nanorods). These are separated by an air gap, which would usually stop the electron flow, but because the air gap is less than 1nm, the electrons can ‘tunnel’ through.

Most of the tunnelling electrons arrive at the gold nanorod tips in the form of ‘hot electrons’, but a small proportion excite plasmons in the metamaterial to emit light whose wavelength is directly related to the applied voltage.

According to the team, this conversion is usually inefficient, but the use of array gold nanorods provides 100billion tunnel junctions, improving electron-to-plasmon conversion and making the emitted light visible.

While there are applications in sensing, the researchers point to a benefit in small scale electronics. Since light is generated by applying a voltage along a 10nm thick nanorod, it can be used to transmit information optically between or within chips. The metamaterial allows optical signals to be produced within a much smaller device, holding the potential of faster electronics.

King’s College Professor Anatoly Zayats added: “When we began these studies, we expected to generate some weak light which we thought should be enough for various nanophotonic applications. But as sometimes happens in the research, the applications are much richer.”

Graham Pitcher

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