Scientists make advancements in field of plasmonics

Photo: A new development was created through research in plasmonics.
Amirpasha Moghtaderi/Staff
A new development was created through research in plasmonics.

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In an age when technological grandeur is marked by the speed of a device, scientists at the Lawrence Berkeley National Laboratory have made an advancement in the field of plasmonics that would broaden the range of materials used to make, among other things, extremely fast computers.

Plasmonics is a field that studies the interaction of light with nanoscale structures. The research - published online April 10 in the journal Nature Materials - indicates that localized plasmonic surface resonances are not only displayed in metals but can also exist in semiconductor nanocrystals called quantum dots.

This means that the frequency of plasmonic resonances can be manipulated to improve the efficiency of the products in which they are used - such as computers.

According to Prashant Jain, a UC Berkeley postdoctoral researcher who co-authored the study, creating computers that run on plasmons rather than electrons - which is what current computers run on - would be impossible without the controllable frequencies characteristic of plasmonics in semiconductors. Such computers would be faster, as photons travel faster than electrons without losing energy through resistance.

"To create a photonic computer you need all these tiny photonic components," he said. "If you want one that's switchable you can't use a metal, but you can use a semiconductor because their interaction with light can switch on and off."

Yongmin Liu, a postdoctoral researcher in UC Berkeley's Department of Mechanical Engineering, said the relatively small wavelengths of plasma can focus light on small areas. This feature can be used to make patterns on computer chips that would increase density for information storage.

Co-author Joseph Luther, currently a senior research scientist at the National Renewable Energy Lab in Colorado, conducted postdoctoral research with Paul Alivisatos, a corresponding author and director of the Lawrence Berkeley National Laboratory, whose research group helped conduct studies at the lab.

Luther said the team wanted to see if plasmonic properties could arise in non-metallic materials, a theory that had not yet been proven. To do this, they tested the properties of the semiconductor copper-sulfide.

"Since the nanocrystals didn't have as much copper as did sulfur, they're what are called copper vacancies," he said. "When (a copper atom) is not there, you basically have a localized charge in that one vacancy. What we noticed was that they behaved like a metal that had a plasmon."

Four authors - including Jain - found that pure copper sulfide without those vacancies did not demonstrate the same plasmonic qualities.

According to Jain, by exposing the material to a chemical oxidant, researchers "doped" it, which made it an impure substance. This allows it to display plasmonic resonance.

Research has already been conducted on semi-conductors and plasmonic resonance. However, this is the first time plasmonics and semi-conductors have been merged into a single field.

"There were two communities of researchers," Jain said. "One was on nanostructures, photonics and plasmonics. The other was working on semiconductors, quantum dots and the whole nanoelectronics and computer fabrication industry. This paper basically combines research from both and makes a combined field of quantum dot plasmonics."


Contact Kate Randle at [email protected]

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