Berlin 2015 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 18: Focus Session: Structure, Chemistry, and Ion Solvation at Solid-Liquid Interfaces I
O 18.2: Vortrag
Dienstag, 17. März 2015, 11:00–11:15, HE 101
Probing Water Structure at the α-Al2O3(0001) Surface Using Interface Specific Vibrational Dynamics — Yujin Tong, Harald Kirsch, Martin Wolf, and •R. Kramer Campen — Fritz-Haber-Institut, Abt. Physikalische Chemie, 14195 Berlin, Germany
α-Al2O3(0001) surfaces exposed to water are ubiquitous in engineered applications and a useful model for more complicated alumino-silicate surface/water interaction omnipresent in the environment. Despite this ubiquity, gaining a molecular level understanding of water α-Al2O3(0001) interaction has proven challenging. It has recently been proposed, based partly on simulation, that the first layer of water on this surface is essentially hydrophobic: while hydrogen bonding occurs within this first layer, neither surface aluminols nor the first layer of molecular water donate a hydrogen bond to overlying bulk liquid. Direct experimental evidence for such a non-wetted water layer has thus far proven elusive. Here we probe the existence of this layer using interface specific vibrational relaxation as a probe of surface water structure. We find, using an ultrafast time resolved infrared pump - vibrational sum frequency probe scheme, that the T1 of OH groups at the α-Al2O3(0001) surface is ≈ 8 ps: intermediate between that of surface aluminols in contact with excess water (< 1 ps) and that of isolated surface OH groups on oxide surfaces (> 100 ps). This intermediate T1 is the first direct experimental insight consistent with a non-wetted interfacial water layer on the α-Al2O3(0001) surface.