The secrets behind the mysterious nano-sized electromagnetic "hotspots" that appear on metal surfaces under a light are finally being revealed with the help of a BEAST. Researchers at the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a single molecule imaging technology, dubbed the Brownian Emitter Adsorption Super-resolution Technique (BEAST), that has made it possible for the first time to directly measure the electromagnetic field inside a hotspot. The results hold promise for a number of technologies including solar energy and chemical sensing.
"With our BEAST method, we were able to map the electromagnetic field profile within a single hotspot as small as 15 nanometers with an accuracy down to 1.2 nanometers, in just a few minutes," says Xiang Zhang, a principal investigator with Berkeley Lab's Materials Sciences Division and the Ernest S. Kuh Endowed Chaired Professor at the University of California (UC), Berkeley. "We discovered that the field is highly localized and, unlike a typical electromagnetic field, does not propagate through space. The field also has an exponential shape that rises steeply to a peak and then decays very fast."
Zhang, who directs the Center for Scalable and Integrated NanoManufacturing (SINAM), a National Science Foundation Nano-scale Science and Engineering Center at UC Berkeley, is the corresponding author of a paper on this research that appears in the journal Nature under the title "Mapping the Distribution of Electromagnetic Field Inside a 15nm Sized Hotspot by Single Molecule Imaging." Co-authoring the paper with Zhang were Hu Cang, Anna Labno, Changgui Lu, Xiaobo Yin, Ming Liu and Christopher Gladden.
Under optical illumination, rough metallic surfaces will become dotted with microscopic hotspots, where the light is strongly confined in areas measuring tens of nanometers in diameter, and the Raman (inelastic) scattering
|Contact: Xiang Zhang|
DOE/Lawrence Berkeley National Laboratory