Analysis of thin-film polymers using attenuated total internal reflection-Raman microspectroscopy

Area of Science:

• Materials Science
• Spectroscopy
• Analytical Chemistry

Background:

• Molecular surface and thin-film analysis are crucial in various scientific fields.
• Attenuated total reflection infrared (ATR-IR) and confocal Raman microspectroscopy are established techniques.
• ATR-IR's penetration depth is wavelength-dependent, suggesting Raman spectroscopy's potential for thinner films.

Purpose of the Study:

• To investigate the largely unexplored technique of Attenuated Total Reflection Raman Microspectroscopy (ATR Raman).
• To explore the theoretical sampling depth of ATR Raman microspectroscopy for thin-film analysis.
• To assess the feasibility of micro-ATR Raman for analyzing polymer films on substrates.

Main Methods:

• A Renishaw inVia Raman microscope was externally modified for ATR Raman experiments.
• A solid immersion lens (SIL) was employed to enhance ATR Raman capabilities.
• Thin-film polymer samples (60-200 nm thickness) on a thicker substrate were analyzed.

Main Results:

• ATR Raman spectra were successfully collected from polymer films ranging from 200 nm to 60 nm in thickness.
• Substrate interference was not observed until the thin film thickness reached 68 nm.
• The study explored sampling depths with and without the SIL, and with evanescent excitation.

Conclusions:

• Micro-ATR Raman microspectroscopy is a feasible technique for analyzing thin polymer films.
• The method allows for the analysis of films down to 60 nm without detecting the underlying substrate.
• ATR Raman offers a promising approach for high-resolution surface and thin-film analysis.