New Type of Electron Wave Observed

“The existence of this wave means that the electrons on the surfaces of copper, iron, beryllium and other metals behave like water on a lake’s surface,” says Bogdan Diaconescu, a postdoctoral research associate in the Condensed Matter Group of the physics department at University of New Hampshire. “When a stone is thrown into a lake, waves spread radially in all directions. A similar wave can be created by the electrons on a metal surface when they are disturbed, for instance, by light.”

Acoustic surface plasmons have long been predicted on merely theoretical grounds, their existence has been extraordinarily difficult to prove experimentally. The new experiment that found the acoustic surface plasmon used an extremely precise electron gun, which shoots slow electrons on a specially prepared surface of a beryllium crystal. When the electrons are reflected back from the electron lake on the surface of the metal, some of them loose an amount of energy that corresponds to the excitation of an acoustic plasmon wave. This energy loss could be measured with a detector that was placed in an ultra-high vacuum chamber, together with the beryllium sample. The energy loss is small but corresponds exactly to the theoretical prediction.

Research on metal surfaces is important for the development of new industrial catalysts and for the cleaning the exhaust of factories and cars. As the new plasmons are very likely to play a role in chemical reactions on metal surfaces, theoretical and experimental research will have to take them into account as a new phenomenon in the future.

In addition, there are several promising perspectives in nano-microscopy and optical signal processing when the new plasmons are excited directly with light diffracted off very small nano-features. The researchers estimate that, depending on their energy, the waves spread down to a few nanometers , and die out after a few femtoseconds after they have been created, thus witnessing very fast chemical processes on atomic scale.; Source: University of New Hampshire