Suppressed terahertz dynamics of water confined in nanometer gaps

• Published in: Science advances Vol. 10; no. 17; p. eadm7315
• Main Authors: Yang, Hyosim, Ji, Gangseon, Choi, Min, Park, Seondo, An, Hyeonjun, Lee, Hyoung-Taek, Jeong, Joonwoo, Park, Yun Daniel, Kim, Kyungwan, Park, Noejung, Jeong, Jeeyoon, Kim, Dai-Sik, Park, Hyeong-Ryeol
• Format: Journal Article
• Language: English
• Published: United States American Association for the Advancement of Science 26.04.2024
• Subjects: Optics; Physical and Materials Sciences; Physics; SciAdv r-articles
• ISSN: 2375-2548; 2375-2548
• DOI: 10.1126/sciadv.adm7315

Nanoconfined waters exhibit low static permittivity mainly due to interfacial effects that span about one nanometer. The characteristic length scale may be much longer in the terahertz (THz) regime where long-range collective dynamics occur; however, the THz dynamics have been largely unexplored because of the lack of a robust platform. Here, we use metallic loop nanogaps to sharply enhance light-matter interactions and precisely measure real and imaginary THz refractive indices of nanoconfined water at gap widths ranging from 2 to 20 nanometers, spanning mostly interfacial waters all the way to quasi-bulk waters. We find that, in addition to the well-known interfacial effect, the confinement effect also contributes substantially to the decrease in the complex refractive indices of the nanoconfined water by cutting off low-energy vibrational modes, even at gap widths as large as 10 nanometers. Our findings provide valuable insights into the collective dynamics of water molecules which is crucial to understanding water-mediated processes. Suppressed terahertz vibrational modes in nanoconfined water lead to an apparent solid-like behavior as observed experimentally.