Interface-Sensitive Raman Microspectroscopy of Water via Confinement with a Multimodal Miniature Surface Forces Apparatus

TL;DR

This paper introduces a novel multimodal microscope combining a miniature Surface Forces Apparatus with Raman spectroscopy to study water at interfaces with nanometer and single-molecule sensitivity.

Contribution

The work presents a new integrated microscope that simultaneously measures force-distance and Raman spectra at interfaces, enabling chemically-resolved analysis of confined water with high sensitivity.

Findings

Water detected near Teflon-glass interface with nanometer precision

Achieved vibrational spectroscopy sensitivity down to single water monolayer

Enabled label-free, chemically-resolved imaging of confined regions

Abstract

Modern interfacial science is increasingly multi-disciplinary. Unique insight into interfacial interactions requires new multimodal techniques for interrogating surfaces with simultaneous complementary physical and chemical measurements. We describe here the design and testing of a microscope that incorporates a miniature Surface Forces Apparatus ({\mu}SFA) in sphere vs. flat mode for force-distance measurements, while simultaneously acquiring Raman spectra of the confined zone. The microscope uses a simple optical setup that isolates independent optical paths for (i) the illumination and imaging of Newton's Rings and (ii) Raman-mode excitation and efficient signal collection. We benchmark the methodology by examining Teflon thin films in asymmetric (Teflon-water-glass) and symmetric (Teflon-water-Teflon) configurations. Water is observed near the Teflon-glass interface with nanometer-scale sensitivity in both the distance and Raman signals. We perform chemically-resolved, label-free imaging of confined contact regions between Teflon and glass surfaces immersed in water. Remarkably, we estimate that the combined approach enables vibrational spectroscopy with single water monolayer sensitivity within minutes. Altogether, the Raman-{\mu}SFA allows exploration of molecular confinement between surfaces with chemical selectivity and correlation with interaction forces.