Harnessing Phonon Polaritons for Dynamic and Sensitive Hydrogen Detection in the Mid-Infrared.

Area of Science:

• Materials Science
• Nanophotonics
• Chemical Sensing

Background:

• Phonon polaritons offer low-loss light-matter interactions, superior to plasmonics for mid-infrared applications.
• Existing phonon polariton applications primarily focus on solid- and liquid-phase sensing, with gas-phase detection being underexplored.

Purpose of the Study:

• To develop and demonstrate a low-loss phonon polariton platform for enhanced mid-infrared (mid-IR) gas detection.
• To investigate the use of planar and nanostructured palladium/silicon carbide (Pd/SiC) heterostructures for hydrogen (H2) gas sensing.

Main Methods:

• Investigated mid-IR optical properties of Pd/SiC heterostructures under varying gaseous atmospheres, focusing on low H2 concentrations.
• Utilized nanostructured Pd/SiC metasurfaces to create localized phonon polariton modes with high absorption.
• Explored the role of a 25 nm Pd layer as a chemical transducer for H2 adsorption and intercalation.

Main Results:

• Demonstrated phonon-enhanced H2 detection using both unpatterned and nanostructured Pd/SiC substrates.
• Achieved narrowband, highly sensitive, and reversible H2 detection with Pd/SiC metasurfaces, outperforming other mid-IR nanophotonic materials.
• Showcased H2 intercalation into Pd, forming a PdHx phase that modulates the mid-IR dielectric function.

Conclusions:

• The developed Pd/SiC phonon polariton platform enables advanced passive optical H2 sensing in the mid-IR spectrum.
• This technology has potential for integration with IR spectroscopy for dynamic chemical process monitoring and environmental sensing.
• The findings advance gas-phase sensing capabilities, offering new possibilities for *in situ* reaction studies.