Angle-tunable enhanced infrared reflection absorption spectroscopy via grating-coupled surface plasmon resonance.

Area of Science:

• Spectroscopy
• Plasmonics
• Materials Science

Background:

• Surface-enhanced infrared absorption (SEIRA) spectroscopy amplifies weak vibrational signals.
• Current SEIRA methods primarily use localized surface plasmons from metal nanoparticles.
• Research into using propagating surface plasmons for SEIRA is limited.

Purpose of the Study:

• To demonstrate angle-tunable SEIRA enhancement using propagating surface plasmons.
• To investigate the coupling of surface plasmons with polymer vibrational modes.
• To explore the use of diffraction gratings for SEIRA excitation.

Main Methods:

• Fabrication of silver-coated diffraction gratings via laser interference lithography.
• Measurement of infrared reflection absorption spectra of PMMA films on gratings.
• Varying angle, polarization, and grating orientation to isolate plasmon enhancement.
• Optical simulations using rigorous coupled-wave analysis (RCWA).

Main Results:

• Achieved angle-tunable enhancement of polymer (PMMA) vibrational stretching modes.
• Demonstrated signal enhancements exceeding 10-times compared to non-plasmonic conditions.
• Identified plasmon-induced enhancement through optical simulations and experimental variations.
• Correlated grating periodicity with specific vibrational mode overlap.

Conclusions:

• Propagating surface plasmons on diffraction gratings offer an effective route for SEIRA.
• This method provides angle-tunable enhancement for vibrational spectroscopy.
• Laser interference lithography enables precise control over plasmon excitation for SEIRA.