Researchers present new advances to unlock the potential of plasmonics

Plasmonics are special optical phenomena that are understood as interactions between light and matter and possess various shapes, material compositions and symmetry-related behaviors. Designing such nanoscale plasmonic structures can pave the way for optical materials that respond to light orientation (polarization), which is not easily achievable in existing bulk dimensions and materials.

In this regard, “shadow growth” is a technique that uses vacuum deposition to produce nanoparticles from a wide range of 2D and 3D shapes at the nanoscale. Recent advances in research aimed at controlling this shadowing effect have expanded the possibilities for creating different nanostructures.

Now, in two studies led by Assistant Professor Hyeon-Ho Jeong of the Gwangju Institute of Science and Technology (GIST), Republic of Korea, researchers have comprehensively shed light on recent advances in shadow growth techniques for hybrid plasmonic nanomaterials, including hybrid plasmonic nanomaterials. inspired designs containing magnesium (Mg).

The studies were published in Advanced materials on March 25, 2022 (with Jang-Hwan Han and Doeun Kim as co-first authors and Professor Peer Fischer and Dr. Jeong as co-corresponding authors) and Advanced optical materials on November 20, 2023 (with Juhwan Kim and Jang-Hwan Han as co-first authors and Dr. Jeong as corresponding author), respectively.

The shadow effect here refers to the presence of “dark” areas on a surface that are masked by “seed” molecules, and therefore inaccessible for the deposition of vaporized materials, much like the shadow areas that the light cannot reach.

Dr. Jeong explains: “Since these shadow areas are the regions where the material cannot be deposited, a set of three-dimensional nanostructures can be formed. This formation depends on the size of the seed, the spacing between the seeds. , and the inclination of the substrate.

Additionally, says Doeun Kim, a Ph.D. student, “The creation of unique nanostructures is influenced by the introduction of rotation during the process, based on speed, time and angle of rotation, ultimately forming three-dimensional nanostructures.”

In the first study (shown on the cover page), the team demonstrated the production of various nanostructures using a specific shadow growth technique known as oblique angle deposition. These structures exhibit tunable optical properties achieved through appropriate modifications of their material, shape, and environment.

Their review also focuses on a wide range of potential applications, including nano- and micro-robots for wound healing and drug delivery in the human body, photonic devices, and chiral spectroscopy, among others. .

For the subsequent study, the team created 3D rotamers (molecules with specific rotational arrangements) capable of linear and circular polarization, as well as storing a significant amount of information.

This clock-inspired design involves placing two Mg nanorods at a certain changeable angle, resembling the hour and minute hands of a clock. These nanostructures also hold promise for various applications, such as secure verification of items like banknotes, anti-counterfeiting devices, and displays that can shift to desired optical states as needed.

Speaking about these developments and looking ahead to the future of plasmonics, Dr. Jeong says: “These rotamers may have potential use in physically unclonable functions, an area that is currently the subject of intensive research to ensure high levels of safety. robust hardware, such as PCs or servers. »

PhD student Juhwan Kim adds: “In particular, the ability to selectively filter UV light sources and specific visible wavelengths based on polarization state can also be used in glasses and windows to protect eyes and skin by blocking the sun’s UV rays. »