Berlin 2005 – scientific programme

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O: Oberflächenphysik

O 36: Postersitzung (Elektronische Struktur, Grenzfl
äche fest-flüssig, Halbleiteroberfl
ächen und -grenzfl
ächen, Nanostrukturen, Oberfl
ächenreaktionen, Teilchen und Cluster, Struktur und Dynamik reiner Oberfl
ächen)

O 36.22: Poster

Monday, March 7, 2005, 15:00–18:00, Poster TU F

Vibrational Sum-Frequency Spectroscopy of Quartz/Water Interfaces — •Björn Braunschweig and Winfried Daum — Institut für Physik und Physikalische Technologien, TU Clausthal, Leibnizstrasse 4, D-38678 Clausthal-Zellerfeld

We have applied vibrational sum-frequency spectroscopy to examine the ordering of hydrogen-bonded water molecules at quartz/water interfaces and to investigate the structure of the interfacial water layer. Consistent with previous work, our spectra reveal OH stretching bands at ∼ 3200cm⁻¹ and ∼ 3450cm⁻¹ that can be assigned to tetrahedrally and non-tetrahedrally coordinated, hydrogen-bonded water molecules at the interface, respectively. pH-depending variations of the spectra are related to ordering of tetrahedrally coordinated water molecules caused by the electric field of deprotonated silanol groups at the interface. Spectra of thin water films on quartz exhibit a narrow band at 3140cm⁻¹ instead of the broad band at ∼ 3200cm⁻¹ observed for bulk water on quartz. Analysis of the spectra indicates that the broad resonance at 3200cm⁻¹ which in previous work was assigned to the symmetric OH stretching vibration of tetrahedrally bonded water molecules in fact consists of two bands at 3140cm⁻¹ and 3240cm⁻¹ attributable to the symmetric and antisymmetric stretching vibration of tetrahedrally coordinated H₂O, respectively. Comparison of spectra for water films of different thickness leads us to the following model of the interface: the water molecules right on the quartz surface are tetrahedrally coordinated and oriented. The contribution of non-tetrahedrally H₂O observed in our spectra originates from the interfacial region above the ordered water layer.