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Multiplex Chemical Imaging Based on Broadband Stimulated Raman Scattering Microscopy
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Tip-Enhanced Multipolar Raman Scattering
Chih-Feng Wang1, Zhihua Cheng2, Brian T O'Callahan3
1Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States.
The Journal of Physical Chemistry Letters
|March 12, 2020
Summary
We observed multipolar Raman scattering in tip-enhanced Raman spectroscopy (TERS) of gold nanocubes. This reveals previously unseen chemical information at the nanoscale, crucial for advanced chemical imaging.
Area of Science:
- Plasmonics
- Nanophotonics
- Chemical Imaging
Background:
- Tip-enhanced Raman spectroscopy (TERS) is a powerful technique for nanoscale chemical analysis.
- Conventional TERS signals are primarily dipolar.
- Understanding higher-order scattering is essential for advanced TERS applications.
Purpose of the Study:
- To investigate and identify multipolar Raman scattering contributions in TERS.
- To analyze the role of electric field gradients in TERS spectra.
- To explore the potential of multipolar TERS for chemical reaction mapping.
Main Methods:
- TERS measurements on thiobenzonitrile (TBN)-functionalized gold nanocubes.
- Analysis of spectral signatures in the 1225-1500 cm-1 region.
- Assignment of Raman-forbidden transitions to multipolar scattering phenomena.
Main Results:
- Observed and assigned weak spectral signatures to multipolar Raman scattering (electric dipole-magnetic dipole and electric dipole-electric quadrupole).
- Demonstrated that multipolar scattering can dominate single-pixel TERS spectra.
- Correlated multipolar scattering with spatially varying enhanced electric field gradients.
Conclusions:
- Multipolar Raman scattering is a significant, often overlooked, component of TERS.
- Accurate interpretation of TERS spectral images requires accounting for both dipolar and multipolar contributions.
- This finding is critical for advancing TERS-based chemical reaction mapping.
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