New phenomenon in physics discovered on illumination of metal surfaces
Scientific research at the Centre of the Physics of Materials, a mixed venture of the Higher Council for Scientific Research (CSIC) and the University of the Basque Country (UPV/EHU) in Donostia-San Sebastian, has enabled the discovery of a new physical phenomenon that affects the surfaces of illuminated metals. The conclusions of the research have been published in the journal Nature.
The discovery, known as acoustic plasmon, could have applications in the design of ultra-high velocity electronic devices for data storage, for use in nano-optics or biomaterials, as well as in the creation of new materials for medical applications.
A plasmon is a charged wave formed by the group excitation of electrons. An acoustic plasmon is a type of surface plasmon produced by the interaction between light and metal surfaces.
The main difference between common surface plasmons – known for half a century – and the new, acoustic plasmons is that each of these is created with a different amount of energy. The acoustic plasmon multiplies its possible applications on using less energy.
In concrete, while common surface plasmons need 10 electron-volts of energy to become excited – a relatively high value for many technological applications – the acoustic plasmon can be triggered into an excited state with very low levels of energy input – less than 1 electron-volt.
One of the authors of the research, Eugene Chulkov, who works at the Centre of Materials Physics, explains the find as follows: "When light falls on a metal surface, the metal electrons interact with the electromagnetic field of light and create other waves, called plasmons".
Chulkov provides a more graphic example in order to understand the phenomenom: "The charged waves that produces the light fall on the metallic surface in the same way as ripples are made by a stone thrown into a pond ".
Chulkov admits that it may seem strange to use metallic structures to transmit light, as it is well known that light quickly attenuates on passing through a metal. "Nevertheless", he adds, "the situation is different if one thinks of surface plasmons, given that the waves may travel several centimetres over a surface before losing their energy, a feature that could be useful in biomedicine and nanotechnology".
Research into this phenomenon could be useful in the design of metallic surfaces on a nanometric scale and on which the properties of the plasmons propagated by these surfaces, themselves, may be modified or manipulated.
This work has been led by physicist Pedro Miguel Etxenike, President of the Donostia International Physics Center, in collaboration with scientists from the CSIC, the UPV/EHU, the CIC Nanogune and the Universidad Autónoma of Madrid.
The research team has suggested baptizing the new phenomenon “the Silkin Plasmon” in recognition of the sterling work undertaken by scientist Slava Silkin, who works at the Donostia International Physics Center.
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.