US scientists have developed adjustable nano-antennas that can change light properties

The "pillar fund tie" nanoparticle array in the image demonstrates an adjustable movement when influenced by electromagnetic forces.

Recently, a research team from the University of Illinois at Urbana-Champaign introduced a groundbreaking adjustable nano-antenna system. This technology uses a plasma field controlled by an electronic scanning microscope to enhance mechanical motion, adjust the spacing between nano-antennas, and reconfigure their arrangement. This innovation opens new possibilities for advanced plasmonic light systems and has been featured in recent publications in Nature News.

Plasma nano-antennas feature nano-textured surfaces that can confine and amplify electric fields beyond the diffraction limit, making them increasingly valuable. According to Gimany Tucson, an associate professor of mechanical science and engineering at the university, “The nano-textured surface functions like a pre-programmed script. When light interacts with it, its properties change. Our method allows us to do this dynamically.” By using pre-fabricated nanoarray structures, researchers can adjust the arrays under a scanning electron microscope, enabling further reorganization of plasmonic optical properties. This means the desired nanostructure can be determined after fabrication, rather than before.

According to a recent report from the Physics Organization Network, the team developed columnar-tie nano-antenna (p-BNA) arrays. Each p-BNA is approximately 250 nanometers in diameter, made of gold in a bowtie shape, with a 500-nanometer-tall glass column beneath. The size of the gap in a single p-BNA can be reduced by about 5 nanometers—four times smaller than what conventional lithography techniques can achieve.

Experiments showed that an electron beam from a standard scanning electron microscope (SEM) can deform one or more subarrays of p-BNAs at a speed of 60 nanometers per second. Dr. Brian Locksworth, the paper’s first author and a Ph.D. candidate in electrical and computer engineering, explained, “We observed that the electron excitation caused significant deformation in the nano-antenna, leading to a noticeable change in the gap between gold particles. The force difference was on the order of nanoNewtons (10⁻⁹ N).” The team believes the high aspect ratio of the p-BNA columns (4.2) and the surrounding heat contribute to their sensitivity to minute forces from the electron beam, resulting in movement.

The researchers highlighted three key contributions of their work: First, they achieved precise control over the plasmonic response of individual nano-antennas. Second, they provided unique spatial addressing for sensing and nanoparticle manipulation in nano-photonic devices. Third, they created a platform for studying mechanical, electromagnetic, and thermal phenomena at the nanoscale.

“Our manufacturing process is truly innovative,” said the research team’s Abu Dbuya. “Producing plasmonic nano-antenna structures under an SEM overcomes limitations of traditional lithographic methods. We can now reduce the nano-antenna gap by 5 nanometers. This new technique also opens up exciting opportunities for research in various other fields.”

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