Analysis of Interfacial Water at a Hydrophilic Silicon Surface by in-Situ FTIR/Internal Reflection Spectroscopy

In-situ FTIR/internal reflection spectroscopy (FTIR/IRS) has been used to spectroscopically characterize interfacial water near the hydrophilic surface of a silicon single-crystal internal reflection element. Interfacial water was examined spectroscopically over certain distances from the surface by appropriate design of the geometry and optics of the internal reflection system, thus creating an integrated depth profile of the water structure. The in-situ FTIR/IRS spectra were characterized by consideration of the O−H stretching region (3000−3800 cm-1) associated with the vibrational spectra of interfacial water. The broad peak in this region was deconvoluted in order to isolate overlapping spectral features that indicate the nature of hydrogen bonding in interfacial water. Three distinct bands were found: ∼3600 cm-1 (free OH), ∼3400 cm-1 (incomplete tetrahedral coordination), and ∼3240 cm-1 (complete tetrahedral coordination). Preliminary analysis of these spectral bands indicates the presence of an icelike water structure (∼3240 cm-1) at the hydrophilic silicon surface. This icelike structure decreases in significance away from the interface, as established from spectroscopic depth profile measurements.