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Submolecular-Resolution Probing of Vibrational Anharmonicity Using Tip-Enhanced Raman Spectroscopy
Youngwook Park1, Ikutaro Hamada2, Martin Wolf1
1Department of Physical Chemistry, Fritz-Haber Institute of the Max-Planck Society, Berlin, Germany.
Angewandte Chemie (International Ed. in English)
|September 25, 2025
Summary
This study demonstrates submolecular resolution detection of molecular vibrations using tip-enhanced Raman spectroscopy (TERS). This technique enhances weak signals from overtones and combination bands, revealing vibrational energy transfer at the nanoscale.
Area of Science:
- Chemical Physics
- Surface Science
- Spectroscopy
Background:
- Vibrational spectroscopy offers chemical insights at the atomic scale using confined optical probes.
- Overtones and combination bands in vibrational spectroscopy are typically weak due to low transition moments, limiting their utility.
- Tip-enhanced Raman spectroscopy (TERS) enhances Raman signals near a metallic tip, enabling high-resolution chemical analysis.
Purpose of the Study:
- To achieve submolecular-resolution detection of intense overtones and combination bands using TERS.
- To analyze mechanical and electrical anharmonicities with submolecular contrast.
- To investigate vibrational energy exchange at the submolecular scale.
Main Methods:
- Utilized tip-enhanced Raman spectroscopy (TERS) with a highly confined optical probe.
- Employed an asymmetric perylene derivative on a silicon substrate.
- Investigated the point-contact mode of TERS for enhanced signal detection.
Main Results:
- Achieved submolecular-resolution detection of intense overtones and combination bands.
- Observed a ~10-fold enhancement in Raman signal upon tip-molecule contact.
- Distinguished and analyzed mechanical and electrical anharmonicities with submolecular contrast.
- Revealed spatial variations in mechanical anharmonicity, indicating submolecular vibrational energy transfer.
Conclusions:
- Point-contact mode TERS enables the detection of weak vibrational modes with unprecedented submolecular resolution.
- Anharmonicity analysis at the submolecular level provides insights into molecular potential energy surfaces and polarizability.
- This technique opens avenues for real-space mapping of vibrational energy transfer processes.
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