2022-04-08 スイス連邦工科大学ローザンヌ校(EPFL)
・「金と銀の合金を作れば、両金属の光学効果を一つの材料で実現できると考えた」と、同研究所を率いるオリヴィエ・マルタン教授は語る。従来の金と銀の合金は、800～1,000℃の高温で作製される。しかし、このプロセスでは、ナノ構造の形が変わってしまう。
・EPFLの技術者たちは、あらゆる混合合金に適用できる低温アニール法の開発に着手し,300℃で8時間、さらに450℃で30分加熱し、金と銀の合金薄膜の作製に成功した。
・この発見は、コンタクトレンズ、ホログラフィック光学素子、その他の光学部品の製造に役立つと思われる。
＜関連情報＞
- https://actu.epfl.ch/news/maintaining-the-structure-of-gold-and-silver-in-al/
- https://onlinelibrary.wiley.com/doi/10.1002/adma.202108225
合金ナノ構造・メタサーフェスの低温アニール法: 新たな自由度を開拓する A Low-Temperature Annealing Method for Alloy Nanostructures and Metasurfaces: Unlocking a Novel Degree of Freedom
Debdatta Ray,Hsiang-Chu Wang,Jeonghyeon Kim,Christian Santschi,Olivier J. F. Martin
Wiley Online Library
First published: 15 February 202
https://doi.org/10.1002/adma.202108225
Abstract
The material and exact shape of a nanostructure determine its optical response, which is especially strong for plasmonic metals. Unfortunately, only a few plasmonic metals are available, which limits the spectral range where these strong optical effects can be utilized. Alloying different plasmonic metals can overcome this limitation, at the expense of using a high-temperature alloying process, which adversely destroys the nanostructure shape. Here, a low-temperature alloying process is developed where the sample is heated at only 300 °C for 8 h followed by 30 min at 450 °C and Au–Ag nanostructures with a broad diversity of shapes, aspect ratios, and stoichiometries are fabricated. Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses confirm the homogeneous alloying through the entire sample. Varying the alloy stoichiometry tunes the optical response and controls spectral features, such as Fano resonances. Binary metasurfaces that combine nanostructures with different stoichiometries are fabricated using multiple-step electron-beam lithography, and their optical function as a hologram or a Fresnel zone plate is demonstrated at the visible wavelength of λ = 532 nm. This low-temperature annealing technique provides a versatile and cost-effective way of fabricating complex Au–Ag nanostructures with arbitrary stoichiometry.
