麻豆淫院

In typical plasmonic devices, electromagnetic waves crowd into tiny metal structures, concentrating energy into nanoscale dimensions. Due to coupling of electronics and photonics in these metal nanostructures, plasmonic devices could be harnessed for high-speed data transmission or ultrafast detector arrays. However, studying plasmonic fields in nanoscale devices presents a real roadblock for scientists, as examining these structures inherently alters their behavior.

鈥淲hether you use a laser or a light bulb, the wavelength of light is still too large to study plasmonic fields in nanostructures. What鈥檚 more, most tools used to study plasmonic fields will alter the field distribution鈥攖he very behavior we hope to understand,鈥� says Jim Schuck,  a staff scientist with Lawrence Berkeley National Laboratory (Berkeley Lab) who works in the Imaging and Manipulation of Nanostructures Facility at the Molecular Foundry.

Light microscopy plays a fundamental role in a scientist鈥檚 repertoire: the technique is easy to use and doesn鈥檛 inflict damage to a carefully crafted electronic circuit or delicate biological specimen. However, a typical nanoscale object of interest鈥攕uch as a strand of DNA or a quantum dot鈥攊s well below the wavelength of visible light in size, which means the ability to distinguish one such object from another when they are closely spaced is lost.  Scientists are now challenging this limit using 鈥榣ocalization鈥� techniques, which count the number of photons emanating from an object to help determine its position.

In previous work, Schuck and colleagues at the Molecular Foundry, a U.S. Department of Energy (DOE) Nanoscale Science Research Centers,  engineered bowtie-shaped plasmonic devices designed to capture, filter and steer light at the nanoscale. These nano-color sorter devices served as antennae to focus and sort light in tiny spaces to a desired set of colors or energies鈥攃rucial for filters and other detectors.

In this latest advance, Schuck and his Berkeley Lab team used their innovative imaging concept to visualize plasmonic fields from these devices 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鈥攐scillations of charge that result in optical resonance鈥攋ust a few nanometers apart.

鈥淲e wondered whether there was a way to use light already present in our bowties鈥攍ocalized photons鈥攖o probe these fields and serve as a reporter,鈥� says Schuck. 鈥淥ur 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.鈥�

In parallel with Schuck鈥檚 experimental findings, Jeff Neaton, Director of the Molecular Foundry 鈥檚 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.

鈥淏y shifting their structure by just a few nanometers, we can focus light at different positions inside the bowtie with remarkable certainty and predictability,鈥� said McLeod. 鈥淭his work demonstrates that these nanoscale optical antennae resonate with light just as our simulations predict.鈥�

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鈥檚 Network for Computational Nanotechnology.

鈥淭his work really exemplifies the very best of what the Molecular Foundry is about,鈥� said Neaton, who is also Acting Deputy Director of Berkeley Lab鈥檚 Materials Sciences Division. 鈥淭hree separate Foundry facilities鈥擨maging, Nanofabrication and Theory鈥攃ollaborated on a significant advance in our understanding of how visible light can be localized, manipulated, and imaged at the nanoscale.鈥�

A paper reporting this research titled, 鈥淣on-perturbative visualization of nanoscale plasmonic field distributions via photon localization microscopy,鈥� appears in 麻豆淫院ical 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.

Portions of this work at the Molecular Foundry were supported by DOE鈥檚 Office of Science.  Support for this work was also provided by the National Science Foundation through the Network for Computational Nanotechnology.