Plasmonics is a special optical phenomenon that is understood as the interaction between light and matter and has a variety of shapes, material compositions, and symmetry-related behavior. Designing these plasmonic structures at the nanoscale could pave the way for optical materials that respond to the direction (polarization) of light, which is not easily achievable at bulk scale and in conventional materials. In this regard, “shadow growth” is a technique that utilizes vacuum deposition to produce nanoparticles in a wide range of 2D and 3D geometries at the nanoscale. Recent advances in controlling this shadowing effect have broadened the possibilities for creating a variety of nanostructures.
Now, in a twin study led by Assistant Professor Hyunho Jeong at the Gwangju Institute of Science and Technology (GIST), South Korea, researchers have comprehensively uncovered recent advances in shadow growth techniques for hybrid plasmonic nanomaterials, including clock-coupled ones. Inspired by designs containing magnesium (Mg). The study was published in: Advanced materials March 25, 2022 (Co-first authors are Jang-Hwan Han and Do-Eun Kim; co-corresponding authors are Professor Peer Fischer and Dr. Jeong) advanced optical materials November 20, 2023 (co-first authors are Kim Joo-hwan and Han Jang-hwan; corresponding authors are Dr. Jeong).
The shadowing effect here means the existence of “dark” regions of the surface that are inaccessible to the deposition of vaporized material, as well as shadow regions that are hidden by “seed” molecules and therefore cannot be reached by light. Regarding this, Dr. Jeong said, “Because these shadow areas are areas where materials do not precipitate, an array of three-dimensional nanostructures can be formed. This formation depends on the size of the seeds and the spacing between seeds.” , and the inclination of the substrate.” Additionally, there is Dr. Do-eun Kim. This student said, “During the process, rotation is introduced depending on the rotation speed, time, and angle, creating a unique nanostructure, and ultimately forming a three-dimensional nanostructure.” said.
In the first study (featured in our cover article), the team demonstrated the production of a variety of nanostructures using a specific shadow growth technique known as oblique angle deposition. These structures exhibit tunable optical properties achieved through appropriate modifications to the material, shape, and surrounding environment. Their review also highlights a wide range of potential applications, including nano- and microrobots, photonic devices, chiral spectroscopy, etc. for wound healing and drug delivery in the human body.
For follow-up studies, the team created 3D rotamers (molecules with a specific rotational arrangement) that are capable of linear and circular polarization and can store significant amounts of information. This clock-inspired design involves placing two nanorods made of Mg at specific modifiable angles, similar to the hour and minute hands of a clock. These nanostructures are also promising for a variety of applications, such as security verification of items such as banknotes, anti-counterfeiting devices, and displays that can switch to desired optical states as needed.
Talking about these developments and envisioning the future of plasmonics, Dr. Jeong said, “These rotamers have the potential to be exploited for physically unclonable functions, an area currently under intensive research to ensure robust levels of security in hardware such as PCs and servers. “It can happen,” he said. To elaborate further, the Ph.D. Student Kim Joo-hwan said, “In particular, the ability to selectively filter ultraviolet light sources and specific visible light wavelengths depending on the polarization state can be used on glass and windows to protect eyes and skin by blocking ultraviolet rays from sunlight.”