QUANTA

Tuesday, April 19, 2011


Plasmonic resonances in quantum dots allow for smaller, faster chips

April 19, 2011

Researchers at Berkeley Lab have shown that plasmonic properties can be achieved in the semiconductor nanocrystals known as quantum dots.

To date, plasmonic properties have been limited to nanostructures that feature interfaces between noble metals and dielectrics. The new research extends the range of candidate materials for plasmonics to include semiconductors.

The researchers made quantum dots from the semiconductor copper sulfide. Directing an electromagnetic field at such an interface generates electronic surface waves that roll through the conduction electrons on the metal. The energy in the electronic surface wave is carried in a quantized particle-like unit called a plasmon.

By introducing enough free electrical charge carriers via dopants and vacancies, the researchers were able to achieve localized surface plasmon resonance (LSPR), in which the oscillation frequency between the plasmons and incident photons matches in the near-infrared range of the electromagnetic spectrum.

The promise of plasmonics

The term “plasmonics” describes a phenomenon in which the confinement of light in dimensions smaller than the wavelength of photons in free space make it possible to match the different length-scales associated with photonics and electronics in a single nanoscale device. Scientists believe that through plasmonics it should be possible to design computer chip interconnects that are able to move much larger amounts of data much faster than today’s chips.

It should also be possible to create microscope lenses that can resolve nanoscale objects with visible light, a new generation of highly efficient light-emitting diodes, and supersensitive chemical and biological detectors, as well as solar photovoltaics and artificial photosynthesis. There is even evidence that plasmonic materials can be used to bend light around an object, thereby rendering that object invisible.

“Our study represents a paradigm shift from metal nanoplasmonics as we’ve shown that, in principle, any nanostructure can exhibit LSPRs so long as the interface has an appreciable number of free charge carriers, either electrons or holes,” says Berkeley Lab researcher Prashant Jain. “Unlike a metal, the concentration of free charge carriers in a semiconductor can be actively controlled by doping, temperature, and/or phase transitions.

“Therefore, the frequency and intensity of LSPRs in dopable quantum dots can be dynamically tuned. The LSPRs of a metal, on the other hand, once engineered through a choice of nanostructure parameters, such as shape and size, is permanently locked-in.”

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Publisher and/or Author and/or Managing Editor:__Andres Agostini ─ @Futuretronium at Twitter! Futuretronium Book at http://3.ly/rECc