A team of scientists from the National Institute of Standards and Technology (NIST) and the University of Maryland, College Park, have discovered how to make nanoscale measurements of critical properties of plasmonic nanomaterials, specially engineered nanostructures that modify the interaction of light and matter for a variety of applications, including sensors, photovoltaics, and therapeutics.
Their technique allows researchers to make actual physical measurements of these materials at the nanoscale without affecting their function. Plasmonic nanomaterials contain specially engineered conducting nanostructures, which can be adjusted by saize and shape to tune these interactions between light and adjacent matter. Researchers need to be able to measure the optical properties of individual structures and how each interacts with surrounding materials directly in a way that doesn't affect how the structure functions.
They say that their experimental technique is extremely sensitive spatially and chemically, and the results are straightforward to interpret. The research team used photothermal-induced resonance (PTIR), an emerging chemically specific materials analysis technique, and showed it can be used to image the response of plasmonic nanomaterials excited by infrared (IR) light with nanometer-scale resolution.
The team used PTIR to image the absorbed energy in ring-shaped plasmonic resonators. The nanoscale resonators focus the incoming IR light within the rings' gaps to create "hot spots" where the light absorption is enhanced, which makes for more sensitive chemical identification. For the first time, the researchers precisely quantified the absorption in the hot spots and showed that for the samples under investigation, it is approximately 30 times greater than areas away from the resonators.
The researchers also showed that plasmonic materials can be used to increase the sensitivity of IR and PTIR spectroscopy for chemical analysis by enhancing the local light intensity, and thereby, the spectroscopic signal. They say that PTIR doesn't require the researcher to have prior knowledge about the material’s optical properties or geometry, and it returns data more easily interpretable than other techniques that require separating the response of the sample from response of the probe.
