Rice Researchers Gain New Insight Into Nanoscale Optics

The research is available online from the journal Nano Letters and will appear in an upcoming print edition.

"We've discovered a universal relationship between the behaviorof light and electrons," said study co-author Peter Nordlander,professor of physics and astronomy and of electrical and computerengineering. "We believe the relationship can be exploited to createnanoscale antennae that convert light into broadband electrical signalscapable of carrying approximately 1 million times more data thanexisting interconnects."

Both light and electrons share similar properties, at timesbehaving like waves, at other times like particles. Many interestingsolid-state phenomena, such as the scattering of atoms off surfaces andthe behavior of quantum devices, can be understood as wavelikeelectrons interacting with discrete, localized electrons. Now, Riceresearchers have discovered and demonstrated a simple geometry wherelight behaves exactly as electrons do in these systems.

In recent years there has been intense interest in developingways to guide and manipulate light at dimensions much smaller thanoptical wavelengths. Metals like gold and silver have ideal propertiesto accomplish this task. Special types of light-like waves, calledplasmons, can be transmitted along the surfaces of metals in much thesame way as light in conventional optical fibers.

When small metallic nanoparticles are positioned on the metalfilm, they behave like tiny antennae that can transmit or receivelight; it is this behavior that has been found to mimic that ofelectrons. Until now, the coupling of light waves into extendednanoscale structures has been poorly understood.

Nordlander's research was conducted under the auspices ofRice's Laboratory for Nanophotonics (LANP), a multidisciplinary groupthat studies the interactions of light with nanoscale particles andstructures. The study was co-authored by LANP Director Naomi Halas, theStanley C. Moore Professor of Electrical and Computer Engineering andprofessor of chemistry.The findings stem from a relatively new area ofresearch called plasmonics, which is a major LANP research thrust.

In the latest research, Halas' graduate student Nyein Lwinplaced a tiny sphere of gold -- measuring about 50 nanometers indiameter, within just a few nanometers of a thin gold film. When alight excited a plasmon in the nanosphere, this plasmon was convertedinto a plasmon wave on the film, for certain specific film thicknesses.

The experiments confirmed theoretical work by Nordlander'sgraduate student Fei Le, who showed that the interactions betweenthin-film surface plasmons and the plasmons of nearby nanoparticleswere equivalent to the "standard impurity problem," awell-characterized phenomenon that condensed matter physicists havestudied for more than four decades.

Other co-authors on the paper include Halas's graduate studentJennifer Steele, now a Professor at Trinity University, and formerTexas Instruments Visiting Professor MikaelKäll of Chalmers University of Technology in Gothenburg, Sweden.

The research was funded bythe Army Research Office, the Air Force Office of Scientfic Research,the Welch Foundation, the National Science Foundation, NASA and TexasInstruments.