Researcher Jason Hafner calls them "nanobelts," microscopic strips of gold that could become part of highly tunable sensors or nanomedical devices. [Lindsey et al., Nano Lett., DOI 10.1021/n1203085t].

Nanobelts represent a unique way to manipulate light at the microscopic scale. They join smaller nanoparticles like gold nanorods and nanoshells that can be tuned to absorb light strongly at certain wavelengths and then steer the light around or emit it in specific directions.
The effect is due to surface plasmons, which occur when free electrons in a metal or doped dielectric interact strongly with light. When prompted by a laser, the sun or other energy source, they oscillate like ripples on a pond and re-emit energy either as light or heat. They are the focus of much research for their potential benefits in biomedical applications, molecular sensing and microelectronics.
Nanobelts are unique because the plasmonic waves occur across their width, not along their length, Hafner said. "My intuition says that isn't likely. Why would you get a sharp resonance in the short direction when the electrons can go long? But that's what happens."
Nanobelts scatter light at a particular wavelength (or color), depending on the aspect ratio of their cross sections – width divided by height. That makes them highly tunable, Hafner said, by controlling that aspect ratio.
The team has grown nanobelts up to 100 microns long that range from basic square cross sections -- 25-by-25 nanometers -- to flattened, at 100 nanometers wide by 17 nanometers high. They found that the flatter the nanobelt, the more the scattered light shifted toward red.
"People have studied electrons moving the long way in these kinds of materials, but when they get too long the resonances detune out of the visible and the peaks become so broad that there's no sharp resonance anymore," Hafner said. "We're going across the nanobelt, so length doesn't matter. The nanobelt could be a meter long and still show sharp plasmon resonance."
This story is reprinted from material from Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source