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 backside probing geometry. This new substrate can be very useful for SFG studies of various chemisorbed organic molecules, particularly biological compounds, in aqueous environments.
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