The phenomenon of nanometer-sized metal structures being heated by light has attracted attention in a wide range of fields, including local control of chemical reactions, medical applications, and energy conversion. Until now, it has been believed that when light is applied to metal nanostructures, the entire surface becomes isothermal.
A collaborative study was conducted by a group made up of Associate Professor Kenji Setoura of the Graduate School of Engineering at University of Hyogo, Associate Professor Tomoya Oshikiri of the Institute of Multidisciplinary Research for Advanced Materials at Tohoku University, Assistant Professor Mamoru Tamura of the School of Science at Kwansei Gakuin University, Doctoral Student Ken Morita of the Graduate School of Advanced Science and Engineering at Waseda University, Professor Kohei Imura of the Faculty of Science and Engineering at Waseda University, Professor Hideki Fujiwara of the Faculty of Engineering at Hokkai-Gakuen University, Team Leader Satoshi Ishii of the National Institute for Materials Science, Master's Student Yusuke Fujii of the Graduate School of Chemical Sciences and Engineering at Hokkaido University, Professor Yasutaka Matsuo of the Research Institute for Electronic Science at Hokkaido University, and Professor Takuya Iida of the Graduate School of Science at Osaka Metropolitan University.
The study revealed that when nanostructures are created from titanium nitride, completely different temperature patterns appear on the nanostructure surface solely through the difference in polarization rotation between right-handed and left-handed circularly polarized light. The group's results were published in Nano Letters.
The group hypothesized that when light is irradiated onto nanostructures made of materials with low thermal conductivity, the vibration pattern of electron waves known as localized surface plasmon should be clearly transferred to the surface temperature distribution of the nanostructure.
Therefore, they designed an S-shaped nanostructure made of titanium nitride with a total length of 800 nanometers using numerical simulation. The simulation suggested that when laser irradiation is applied to this S-shaped nanostructure with fixed wavelength and intensity, changing only the rotation direction of circularly polarized light between right-handed and left-handed results in completely different temperature patterns appearing on the surface of the nanostructure.
To verify this, the group fabricated an actual S-shaped nanostructure using electron beam lithography and other techniques and conducted demonstration experiments using laser irradiation. In the experiments, hydrothermal synthesis of zinc oxide, wherein products are formed through thermal reactions, was induced by laser irradiation of this S-shaped nanostructure and results consistent with the simulation were obtained. In other words, it was demonstrated that by using titanium nitride, it is possible to "heat only the target locations on the nanostructure" with light.
In this study, it was demonstrated that temperature patterns in the nanometer-scale microscopic region can be freely shaped "simply by changing the color or polarization of light," challenging the conventional wisdom of plasmonic heating. These results are expected to lead to new technologies for local control of chemical reactions and manipulation of microscopic liquid flow and material transport.
Journal Information
Publication: Nano Letters
Title: Chiral Plasmonic Surface Temperature Switching by Several Tens of Kelvins in Titanium Nitride Nanostructures
DOI: 10.1021/acs.nanolett.5c05212
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