Broadband tunable nanostructures for surface-enhanced infrared absorption spectroscopy.

Area of Science:

• Plasmonics
• Nanophotonics
• Spectroscopy

Background:

• Surface-enhanced infrared absorption (SEIRA) spectroscopy utilizes nanostructures to amplify infrared absorption signals.
• Nanorods of varying lengths offer different plasmon resonance wavelengths, enabling broadband SEIRA.
• Multi-nanorod structures can exhibit dual resonance modes for enhanced spectral properties.

Purpose of the Study:

• To systematically investigate the far-field and near-field properties of multi-nanorod structures for broadband SEIRA.
• To introduce and explore the effect of the X-shape angle as a tunable parameter in nanorod structures.
• To optimize nanostructure design for improved SEIRA performance, particularly for low-noise multi-molecule measurements.

Main Methods:

• Fabrication and characterization of multi-nanorod structures (1-4 nanorods) with varying lengths and X-shaped configurations.
• Systematic investigation of far-field and near-field optical responses as a function of nanostructure geometry, specifically the X-shape angle.
• Analysis of dual-resonance modes and SEIRA hotspot enhancement through simulation and experimental validation.

Main Results:

• X-shaped nanorod structures with dual resonance modes were designed, with the X-shape angle acting as a tunable parameter.
• A strategy was proposed to manipulate far-field amplitudes of dual-resonance modes by adjusting the X-shape angle for broadband SEIRA.
• Introducing a second nanorod to a two-nanorod structure converged far-field amplitudes and increased SEIRA hotspots, while additional nanorods reduced tuning range and enhancement.

Conclusions:

• The angle of X-shaped nanorod structures offers a flexible method to tune broadband SEIRA performance.
• Optimized multi-nanorod configurations, particularly two-nanorod structures, enhance SEIRA hotspots and enable precise control over spectral responses.
• These broadband tunable nanostructures are promising for sensitive, low-noise detection of multiple molecules using SEIRA spectroscopy.