Terahertz Monitoring of Gas-Matter Interactions: Exploring Interatomic and Interfacial Dynamics through Palladium Nano-Film Hybrid Metasurfaces

Terahertz (THz) technology is an attractive optical sensing platform that offers accurate approaches for the real-time investigation of intrinsic materials in non-invasive and non-contact manners. In addition, using metamaterials that have been extensively researched recently, diffraction-limit and absorption cross-section-limit can be overcome [1]. Here, we monitored molecular dynamics by gas-matter interactions including interatomic and interfacial reactions such as absorption, desorption, adsorption, and catalytic reaction. In-situ THz measurement using nano-patterned slot antennas is introduced to investigate Palladium (Pd) based interatomic and interfacial gas-matter interactions. Interatomic interaction which is atomic scale changes can be measured using our geometrically optimized nano-slot structure, which consists of a narrow gap of approximately 14 nm between a gold wall and a deposited Pd metal thin film. Furthermore, we manipulated nano-slot structures to maximize the sensitivity of THz signals in terms of water, formed by the Pd catalytic reactions, and their absorption. Our proposed experiment aims to analyze the dynamics of interatomic hydrogenation, interfacial oxygen adsorption, and water-forming reactions in a highly consistent and dependable manner, enabling real-time analysis [2].<br/>The molecular dynamics are interpreted by THz transmittance measurement under the various gas concentrations including N₂, H_2,and O₂. The molecular dynamics can be determined by inspecting resonance frequency shifts and transmittance changes in the transmitted resonance signals that were filtered by our nano-slot structures. The Pd hydrogenation process, the oxygen adsorptions, and the catalytic water formation reactions according to the various concentrations of H₂, O₂, and N₂ were dynamically measured by resonance frequency and transmittance response.<br/>The atomic scale response, such as hydrogen absorption, desorption into the Pd lattice, and catalytic water formation response which is a relatively huge scale can be measured in a reliable manner using such a long wave-length light. In addition, by interpreting inclinations that are plotted on the map composed of the amount of resonance frequency and transmittance response, not only the three different dynamics can be classified, but also a complex hidden process of water-forming reactions can be tracked.<br/><br/><b>Acknowledgement: </b>NRF (2023R1A2C2003898, CAMM-2019M3A6B3030638, 2021R1A2C2009236), KIST (2E32451)<br/><b>References</b><br/>[1] Nanoscale Terahertz Monitoring on Multiphase Dynamic Assembly of Nanoparticles under Aqueous Environment, Adv. Sci. 8, 11, 2021<br/>[2] Naked-eye observation of water-forming reaction on palladium etalon: transduction of gas-matter reaction into light-matter interaction, PhotoniX, 1, 2023<br/><br/><b>Keywords</b>: Metamaterial, Terahertz spectroscopy, Palladium film