Novel SiO₂-Deposited CaF₂ Substrate for Vibrational Sum-Frequency Generation (SFG) Measurements of Chemisorbed Monolayers in an Aqueous Environment

Abstract

A novel SiO(2)-deposited CaF(2) (SiO(2)/CaF(2)) substrate for measuring vibrational sum-frequency generation (SFG) spectra of silane-based chemisorbed monolayers in aqueous media has been developed. The substrate is suitable for silanization and transparent over a broad range of the infrared (IR) probe. The present work demonstrates the practical application of the SiO(2)/CaF(2) substrate and, to our knowledge, the first SFG spectrum at the solid/water interface of a silanized monolayer observed over the IR fingerprint region (1780-1400 cm(-1)) using a back-side probing geometry. This new substrate can be very useful for SFG studies of various chemisorbed organic molecules, particularly biological compounds, in aqueous environments.

Dissociative Binding of Carboxylic Acid Ligand on Nanoceria Surface in Aqueous Solution: A Joint In Situ Spectroscopic Characterization and First-Principles Study

“…The optically transparent and relatively chemically inert CaF 2 (or BaF 2 ) is suitable for such SFG-VS experiments. It is also possible to use a chemically modified CaF 2 (or BaF 2 ) surface for nanoparticle deposition or molecular layer adsorption studies with SFG-VS. 74 It is our hope that such studies shall lead to direct observations and insights for surface structure and reactivity, especially for site-specific structure and reactivity, of the buried solid/liquid interface.…”

Order of Dry and Wet Mixed-Length Self-Assembled Monolayers

“…Sum frequency generation (SFG) spectroscopy is an ideal technique to characterize SAMs, as it is sensitive to order and surface-specific. By coating a calcium fluoride window with a thin film of SiO 2 , we create a substrate which can support the formation of a silane monolayer, while also being transparent to the visible and IR beams of the SFG . A SAM applied to the SiO 2 -coated CaF 2 may be probed through the substrate so the buried interface of the SAM and another material, such as water, may be studied.…”

Following the Azide‐Alkyne Cycloaddition at the Silica/Solvent Interface with Sum Frequency Generation

“…Therefore a benzyl azide monolayer was prepared on silica using commercially available p ‐azidomethylphenyltrimethoxysilane according to our previously published method 29. As fused silica is opaque in the region where the azide stretch is located (∼2100 cm −1 ), we prepared a SiO 2 thin film on a CaF 2 hemisphere using the method of Ishibashi and co‐workers 30. The functionalized SiO 2 /CaF 2 hemisphere was then placed in contact with methanol in our custom‐built cell and the broadband SFG was measured.…”