Light scattered via nanotubes

CORNELL (US) — Just as walkie-talkies transmit and receive radio waves, carbon nanotubes can transmit and receive light at the nanoscale.

Carbon nanotubes, cylindrical rolled-up sheets of carbon atoms, might one day make ideal optical scattering wires—nano-sized, mostly invisible antennae with the ability to control, absorb, and emit certain colors of light.

Researchers used the Rayleigh scattering of light—the same phenomenon that makes the sky blue—from carbon nanotubes grown in the lab.

While the propagation of light scattering is mostly classical and macroscopic, the color and intensity of the scattered radiation is determined by intrinsic quantum properties.

In other words, the nanotubes’ simple carbon-carbon bonded molecular structure determined how they scattered light, independent of their shape, which differs from the properties of today’s metallic nanoscale optical structures.

“Even if you chop it down to a small scale, nothing will change, because the scattering is fundamentally molecular,” says Jiwoong Park, assistant professor of chemistry and chemical biology at Cornell University.

The research is reported online in the journal Nature Nanotechnology.

The nanotubes’ light transmission behaves as a scaled-down version of radio-frequency antennae found in walkie-talkies, except they interact with light instead of radio waves.

The principles that govern the interactions between light and the carbon nanotube are the same as between the radio antenna and the radio signal.

For the study, Park and colleagues used a methodology that completely eliminates the problematic background signal, by coating the surface of a substrate with a refractive index-matching medium to make the substrate “disappear” optically, not physically.

This technique, which allows seeing the different light spectra produced by the nanotubes, is detailed in another study published in Nano Letters.

The technique also allows quick, easy characterization of a large number of nanotubes, which could lead to ways of growing more uniform batches of nanotubes.

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