Researchers at King’s College London have created a nano-scale device that produces “hot electrons” in a controlled manner.

”Hot electrons” are high-energy electrons that can be used to facilitate unusual chemical reactions. Scientists at King’s College London have created a nanoscale device capable of producing a controlled stream of these “hot electrons,” that due to their high energy, facilitate reactions between chemicals that normally would not interact.

The device is based on a synthesized metamaterial that has unique properties not found in nature. The metamaterial uses the quantum effect known as electron tunneling to convert electrons flowing through a circuit into hot electrons that flow in a stream in a highly controlled manner. The flow of electrons from eutectic gallium indium to gold nanorod, which are separated by an air gap, is generated by applying a voltage across the device.

When the air gap is < 1 nm, quantum mechanics comes into play and the electrons “tunnel” through. As a result, most of the electrons arrive at the gold nanorod tips as hot electrons. A few of the electrons excite plasmons in the metamaterials, resulting in the emission of light at a wavelength correlated to the applied voltage. The electron-to-plasmon conversion is much more efficient in the metamaterial than traditionally observed because of the presence of the array of gold nanorods, making it possible to see the emitted light with the naked eye.

Access to hot electrons may allow the synthetic reactions not previously possible due to the need for very high energies. The ability to incorporate the technology as a lab-on-a-chip device is also attractive as a means for investigating potential new chemistries. In the initial report of this work, the researchers described the use of the hot electrons for oxidation and reduction reactions involving oxygen and hydrogen.

While hot electrons have been produced in the past, they have been generated using light, which leads to excited electrons with a wide range of energies. The new technique produced hot elections with consistent and controllable energy levels that can be tuned for specific energies needed for specific chemical reactions.

In addition, as products are produced in a reaction, they influence the tunneling properties in the metamaterials, leading to a change in the flow of electrons, which be detected through changes in the emitted light. As a result, the device can be used for monitoring of the reactions it is facilitating. Similarly, it can be used as a sensor for monitoring the presence of gases and other molecules. 

“When we began these studies, we expected to generate some weak light, which we thought should be enough for various nanophotonic applications on a chip. But as sometimes happens in research, the applications are much richer,” said King’s College Professor Anatoly Zayats. “We believe the potential of the approach for designing chemical reactions stimulated with hot electrons and monitoring chemical processes for drug and materials discovery is huge.”