2021/01/15
Keio University
Professor Atsushi Nakajima and Project Associate Professor Masahiro Shibuta (at the time of the research; currently a Project Lecturer at Osaka City University) of the Faculty of Science and Technology, Keio University, have revealed that the smallest unit for plasmon response is nine atoms. This was achieved by using the photoelectron emission process from a solid surface onto which nanoclusters with precisely selected numbers of silver atoms were deposited.
In recent years, the utilization of light energy and optical communication technologies have become crucial for the development of carbon-free energy resources and further high-speed communication. Consequently, research and development combining these with nanotechnology are being actively pursued. When light is irradiated onto noble metal particles such as gold and silver, an optical process based on localized surface plasmon resonance (LSPR) occurs. This optical phenomenon has been widely used for coloring glass, as seen in stained glass, Venetian glass, and Edo Kiriko, not to mention the ancient Roman Lycurgus Cup. More recently, applications are anticipated from the perspective of increasing the efficiency of photoelectric conversion devices like solar cells and photonic nanodevices such as plasmonic optical circuits. Clarifying the smallest unit of this LSPR is extremely important for providing a fundamental understanding of plasmon response and for precisely controlling the charge separation process that follows light absorption in photoelectric conversion. Therefore, identifying the origin of LSPR has been strongly desired.
In this study, our research group evaluated the physical properties of LSPR using two-photon photoelectron spectroscopy, in conjunction with the precision synthesis of silver nanoclusters. As a result, by depositing silver nanoclusters with precisely selected numbers of atoms, down to a single atom, onto a solid surface, we determined that silver nanoclusters of nine or more atoms exhibit a plasmon response. We also revealed that the excited electrons generated in silver nanoclusters upon light absorption by plasmons relax very easily within the nanocluster. These findings are considered highly valuable as a fundamental technology for device applications using plasmon response. The results of this research were published in the American Chemical Society's journal "ACS Nano" on January 7, 2021 (US time).
Please see below for the full press release.