Tip-enhanced Raman spectroscopy and imaging: an apical illumination geometry

Area of Science:

• Surface Science and Spectroscopy
• Nanotechnology and Materials Science

Background:

• Tip-enhanced Raman spectroscopy (TERS) offers high-resolution chemical analysis.
• Traditional TERS geometries can face challenges in signal discrimination and surface accessibility.

Purpose of the Study:

• To demonstrate the efficacy of TERS in a top-illumination configuration.
• To investigate the use of radially polarized light for enhanced Raman signal.
• To showcase TERS' capability for sub-diffraction-limited imaging of various surfaces and nanomaterials.

Main Methods:

• Utilized a top-illumination geometry for TERS.
• Employed a radially polarized beam to generate a surface-normal electric field.
• Acquired near-field Raman spectra and performed Raman imaging on Si(100), rhodamine B, brilliant cresyl blue, and carbon nanotubes.

Main Results:

• Achieved a 5x signal enhancement compared to linear polarization due to radial polarization.
• Successfully discriminated near-field TERS signals from the far-field Raman background.
• Obtained sub-diffraction-limited resolution Raman imaging of carbon nanotube distributions on different surfaces (Au, glass, Si).

Conclusions:

• The top-illumination TERS configuration with radial polarization is highly effective for enhanced molecular spectroscopy.
• This method provides significant signal enhancement, facilitating detailed surface analysis and imaging.
• TERS is a powerful tool for investigating molecular distributions on diverse substrates with nanoscale resolution.