Researchers prove existence of new type of electron wave

Jul 04, 2007

New research led by University of New Hampshire physicists has proved the existence of a new type of electron wave on metal surfaces: the acoustic surface plasmon, which will have implications for developments in nano-optics, high-temperature superconductors, and the fundamental understanding of chemical reactions on surfaces.

The research, led by Bogdan Diaconescu and Karsten Pohl of UNH, is published in the July 5 issue of the journal Nature.

“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 Diaconescu, a postdoctoral research associate in the Condensed Matter Group of the physics department at UNH. “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. “Just one year ago, another group of scientists concluded that these waves do not exist,” says Karsten Pohl, associate professor of physics at UNH. “These researchers have probably not been able to find the acoustic plasmon because the experiments require extreme precision and great patience. One attempt after the other did not show anything if, for example, the surface was not prepared well enough or the detectors were not adjusted precisely enough.”

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 (one millionth of a billionth of a second) after they have been created, thus witnessing very fast chemical processes on atomic scale.

Another potential application is using the waves to carry optical signals along nanometer-wide channels for up to few micrometers and as such allowing the integration of optical signal propagation and processing devices on nanometer-length scales. And one of the most interesting but still very speculative applications of the plasmons relates to high temperature superconductivity. It is known today that the superconductivity happens in two-dimensional sheets in the material, which give rise to the special electron pairs which can move without resistance through the conductor.

How this happens precisely is unclear but acoustic plasmons could be part of the explanation. If this is the case, it is a great advantage that it is now possible to study the plasmons on surfaces, where they is much easier to probe them than inside the material.

Citation: Bogdan Diaconescu, Karsten Pohl, Luca Vattuone, Letizia Savio, Philip Hofmann, Vyacheslav M. Silkin, Jose M. Pitarke, Eugene V. Chulkov, Pedro M. Echenique, Daniel Farías y Mario Rocca. Low-energy acoustic plasmons at metal surfaces. Nature, doi:10.1038/nature05975.

Source: University of New Hampshire

Explore further: A new generation of storage—ring

add to favorites email to friend print save as pdf

Related Stories

Gold nanoparticle chains confine light to the nanoscale

22 hours ago

A multidisciplinary team at the Centre d'Elaboration de Matériaux et d'Etudes Structurales (CEMES, CNRS), working in collaboration with physicists in Singapore and chemists in Bristol (UK), have shown that ...

Quantum effects in nanometer-scale metallic structures

Oct 22, 2014

Plasmonic devices combine the 'super speed' of optics with the 'super small' of microelectronics. These devices exhibit quantum effects and show promise as possible ultrafast circuit elements, but current ...

New absorber will lead to better biosensors

Oct 01, 2014

Biological sensors, or biosensors, are like technological canaries in the coalmine. By converting a biological response into an optical or electrical signal, they can alert us to dangers in our external and internal environments. ...

Recommended for you

A new generation of storage—ring

27 minutes ago

A bright synchrotron source that emits over a wide part of the electromagnetic spectrum from the infrared to hard X-rays is currently being built in Lund, Sweden. The MAX IV facility presents a range of technical ...

Universe may face a darker future

4 hours ago

New research offers a novel insight into the nature of dark matter and dark energy and what the future of our Universe might be.

High-intensity sound waves may aid regenerative medicine

22 hours ago

Researchers at the University of Washington have developed a way to use sound to create cellular scaffolding for tissue engineering, a unique approach that could help overcome one of regenerative medicine's ...

Formula could shed light on global climate change

Oct 30, 2014

Wright State University researchers have discovered a formula that accurately predicts the rate at which soil develops from the surface to the underlying rock, a breakthrough that could answer questions about ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.