Gold appears golden in bulk form, but when it becomes nanoparticles at the nanometer scale, it shows a vivid red color. This phenomenon comes from “localized plasmons,” which are coherent waves of electrons in the metal that strongly absorb and scatter specific colors of light from white light. We are developing nanoantennas that use this localized plasmon to efficiently convert light energy into heat.
Gold nanoparticles strongly absorb light through localized surface plasmons and convert it into heat, which has led to many proposed applications such as cancer therapy, catalysis, and solar energy use. However, gold is expensive and has a low melting point, which limits its stability at high temperature. Titanium nitride is now attracting attention because it shows similar optical properties to gold, but also has a very high melting point of about 3000 °C and excellent stability in photothermal conversion. We design and fabricate various nanostructures of titanium nitride by simulation and micro/nano-fabrication, and evaluate their properties and applications. Titanium nitride nanoheaters can be applied to microchannel reaction control, on-chip thermal processes, solar-driven distillation and hydrogen production, and also to information storage such as heat-assisted magnetic recording. They open new directions in nanotechnology to support a sustainable society.
As seen in stained glass windows of Western churches, when gold is finely ground and mixed into glass, it shows a vivid red color, different from the golden color in bulk scale. With the progress of science and technology, it became possible to synthesize colloidal solutions of gold nanoparticles with very uniform size, and with the development of electromagnetism, it was clarified that the bright red color comes from the coherent oscillation of electrons called localized surface plasmons. When light with a frequency matching this plasmon resonance is irradiated to the nanoparticles, they strongly absorb the light and convert the energy into heat. Such photothermal conversion of gold nanoparticles has been actively studied in nanotechnology, and many applications have been proposed, including photothermal cancer therapy, catalytic reactions, and solar-driven water distillation.
The efficient photothermal conversion of nanoparticles by localized plasmons has been well understood in terms of physical mechanisms, but some challenges have been recognized when considering practical applications using gold. First, the recent rise in gold price makes cost a serious issue. Second, although gold is chemically stable, its melting point is low, so nanoparticles easily melt and deform when heated by light. Therefore, titanium nitride is now attracting attention worldwide. Thin films of titanium nitride show a golden metallic luster similar to gold, and when made into nanoparticles, they exhibit good localized plasmon resonance. Moreover, titanium nitride has a very high melting point of about 3000 °C, giving excellent stability under light heating. Our group designs titanium nitride nanoantennas of various sizes and shapes by numerical simulations, fabricates them using microfabrication techniques such as electron-beam lithography, and evaluates their photothermal properties to explore applications in nanotechnology.
Plasmonic nanoheaters made of titanium nitride combine high-temperature stability with excellent photothermal conversion, making them suitable for precise thermal control in small regions. Potential applications include controlling chemical reactions in microfluidic channels, on-chip thermal processes, as well as energy technologies such as solar-driven distillation and hydrogen production. In addition, there is potential for use in information storage, exemplified by the commercially established heat-assisted magnetic recording. These developments are expected to lay a foundation for new nanothermal technologies that contribute to a sustainable society.
| Research | ||
|---|---|---|
| Journal | RSC Advances | |
| Title | Switching nanoscale temperature fields with high-order plasmonic modes in transition metal nanorods | |
| Author | Kenji Setoura, Mamoru Tamura, Tomoya Oshikiri, and Takuya Iida | |
| Member | Kenji Setoura | |
| URL | https://doi.org/10.1039/D3RA06649E | |
| Information on conferences, exhibitions, and other related events | "Switching of surface temperature of plasmonic titanium nitride nanostructures by circularly polarized light", Optical Manipulation and Structured Materials Conference 2025 (SPIE). | |
Learn about the cutting-edge research achievements, advanced technical resources, and know-how that the Graduate School of Engineering at the University of Hyogo can provide. We welcome partners who can create the future together with us by jointly generating new ideas and technologies through collaborative research, commissioned research, and technical consultations.
More
