Photonic Interactions at the Atomic Level
by Richard Merritt
DURHAM, N.C. – By measuring the unique properties of light on the scale of a single atom, researchers from Duke University and Imperial College, London, believe that they have characterized the limits of the ability of metals to be used in devices that rely on the enhancement of light.
This field is known as plasmonics because scientists are trying to take advantage of plasmons, electrons that have been “excited” by light in a phenomenon that produces electromagnetic field enhancement. The enhancement achieved by means of metals at the nanoscale is significantly higher than that achievable with any other material.
Until now, researchers have been unable to quantify plasmonic interactions at very small sizes, and thus have been unable to quantify the practical limitations of light enhancement. This new knowledge should help in the development of devices, such as medical sensors and integrated photonic communications components, since scientists will have a roadmap for precisely controlling the scattering of light.
Typically, plasmonic devices involve the interactions of electrons between two metal particles separated by a very short distance. For the past 40 years, scientists have been trying to figure out what happens when these particles are brought closer and closer, at sub-nanometer distances, according to the Duke electrical engineers.
The results of Ciracì and co-workers’ experiments, which were conducted in the laboratory of senior researcher David R. Smith, William Bevan Professor of electrical and computer engineering at Duke, were published in the journal Science as the cover article.
In their experiments, Ciracì and his team started with a thin gold film coated with a ultra-thin monolayer of organic molecules, studded with precisely controllable carbon chains. Nanometric gold spheres were dispersed on top of the monolayer. Essential to the experiment was that the distance between the spheres and the film could be adjusted with a precision of a single atom. In this fashion, the researchers were able to overcome the limitations of traditional approaches and obtain a photonic signature with atom-level resolution.
The Duke team worked with colleagues at Imperial College, specifically Sir John Pendry, who has long collaborated with Smith.
The research was supported by the Air Force Office of Scientific Research and by the Army Research Office’s Multidisciplinary University Research Initiative (MURI).
The other members of the team were Duke’s Ryan Hill, Jack Mock, Yaroslav Urzhumov and Ashutosh Chilkoti; and from Imperial College, Antonio Fernández-Domínguez and Stefan Maier.