Electron-Tunneling Nanomaterial Could Boost Optoelectronics and Sensing

A material that uses quantum effects and allows precise control of hot electrons shows potential for use in chemical research, optoelectronics and sensing.

Scientists at King’s College London developed the device. It controls high-energy electrons, allowing unusual chemical reactions to take place. The electrically stimulated metamaterial could be used as a highly sensitive gas sensor and a nanoscale light source for optical communications on microchips.

The device takes advantage of a quantum effect called electron tunneling to produce streams of particles that can have important applications, when properly controlled.

A voltage is applied across the device, causing a flow of electrons 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 when the air gap is less than a nanometer, quantum mechanical rules apply, which allow the electrons to "tunnel" through.

This tunneling produces two useful effects.

First, most of the tunneling electrons arrive in the gold nanorod tips in the form of "hot electrons." Hot electrons are of great interest to chemical industries, since their high energies allow chemical reactions to occur between molecules that would not normally react with each other.

Second, a small proportion of the tunneling electrons excite other particles in the metamaterial. These excitations emit light, the wavelength of which is directly related to the applied voltage. Usually this conversion is very inefficient, but the King’s metamaterial uses array gold nanorods providing one hundred billion tunnel junctions to improve the electron-to-plasmon conversion, making the emitted light visible to the naked eye.

The creation of hot electrons is very useful to a wide range of industries that are interested in creating new chemicals that do not occur under normal conditions.

“When we began these studies, we expected to generate some weak light [that] we thought should be enough for various nanophotonic applications on a chip,” said professor Anatoly Zayats of King’s College. “But as sometimes happens in the research, the applications are much richer. 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.”

The research has been published in Nature Nanotechnology (DOI: 10.1038/s41565-017-0017-7).