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February 03, 2011

Berkeley Lab Scientists Image Plasmonic Nanofields with nanoscale resolution


Scientists at Berkeley Lab’s Molecular Foundry have developed a web-based imaging toolkit designed for researchers studying plasmonic and photonic structures. This open-source software is available at http://www.nanohub.org.

Berkeley Lab team used their innovative imaging concepts to visualize plasmonic fields with nanoscale resolution. By imaging fluorescence from gold within the bowtie and maximizing the number of photons collected from their bowtie devices, the team was able to glean the position of plasmonic modes—oscillations of charge that result in optical resonance—just a few nanometers apart.


We wondered whether there was a way to use light already present in our bowties—localized photons—to probe these fields and serve as a reporter,” says Schuck. “Our technique is also sensitive to imperfections in the system, such as tiny structural flaws or size effects, suggesting we could use this technique to measure the performance of plasmonic devices in both research and development settings.



In parallel with Schuck’s experimental findings, Jeff Neaton, Director of the Molecular Foundry ’s Theory of Nanostructured Materials Facility and Alex McLeod, an undergraduate student working at the Foundry, developed a web-based toolkit, designed to calculate images of plasmonic devices with open-source software developed at Massachusetts Institute of Technology. For this study, the researchers simulated adjusting the structure of a double bowtie antenna by a few nanometers to study how changing the size and symmetry of a plasmonic antenna affects its optical properties.

“By shifting their structure by just a few nanometers, we can focus light at different positions inside the bowtie with remarkable certainty and predictability,” said McLeod. “This work demonstrates that these nanoscale optical antennae resonate with light just as our simulations predict.”

Useful for researchers studying plasmonic and photonic structures, this toolkit will be available for download on nanoHUB, a computational resource for nanoscience and technology created through the National Science Foundation’s Network for Computational Nanotechnology.

“This work really exemplifies the very best of what the Molecular Foundry is about,” said Neaton, who is also Acting Deputy Director of Berkeley Lab’s Materials Sciences Division. “Three separate Foundry facilities—Imaging, Nanofabrication and Theory—collaborated on a significant advance in our understanding of how visible light can be localized, manipulated, and imaged at the nanoscale.”

A paper reporting this research titled, “Non-perturbative visualization of nanoscale plasmonic field distributions via photon localization microscopy,” appears in Physical Review Letters and is available to subscribers online. Co-authoring the paper with Schuck, McLeod and Neaton were Alexander Weber-Bargioni, Zhaoyu Zhang, Scott Dhuey, Bruce Harteneck and Stefano Cabrini.

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