Spectroscopy with scanning near-field optical microscopy using photon tunnelling mode

Area of Science:

• Spectroscopy
• Nanotechnology
• Materials Science

Background:

• Raman spectroscopy provides valuable chemical information.
• Scanning near-field optical microscopy (SNOM) offers high spatial resolution.
• Integrating Raman spectroscopy with SNOM presents challenges in signal detection and probe interference.

Purpose of the Study:

• To demonstrate a novel method for performing Raman spectroscopy using scanning near-field optical microscopy (SNOM).
• To overcome limitations of existing SNOM Raman techniques, particularly probe-induced scattering.
• To obtain high-quality Raman spectra of materials under specific conditions.

Main Methods:

• Utilized photon tunneling mode in SNOM.
• Employed an attenuated total reflection (ATR) configuration for sample illumination.
• Employed a sharpened optical fiber probe to collect the evanescent wave perturbed by the sample.
• Minimized Raman scattering originating from the optical fiber probe.

Main Results:

• Successfully demonstrated Raman spectroscopy coupled with SNOM.
• Achieved significant reduction in Raman scattering from the optical fiber probe.
• Enabled excitation of the sample with higher intensity laser light compared to illumination mode SNOM.
• Obtained off-resonance Raman spectra of copper phthalocyanine (CuPc) without surface-enhanced Raman scattering (SERS).

Conclusions:

• The demonstrated photon tunneling SNOM technique is effective for acquiring Raman spectra.
• This method allows for enhanced excitation intensity and reduced probe interference.
• It provides a viable approach for analyzing materials like CuPc without relying on SERS.