Ordered H2O structures on a particularly weakly interacting surface - H2O/Au(111).

Tatyana Kravchuk, Chemistry, Technion, Haifa, Israel

Enter the body of your abstract hereIn  past decades, numerous experimental and theoretical studies have been devoted to understanding the interaction of H₂O with various metallic surfaces. The interaction between water molecules and the Au(111) surface is weaker than that of all the other close packed noble and transition metals, which could suggest that a wetting layer might not form on this substrate. Nevertheless, scanning probe studies have identified the formation of a first layer which serves as a precursor to the 3D growth of H₂O, a layer which was assumed to be amorphous at the temperature range probed by the experiments[1,2] in apparent contradiction with the sqrt(3)xsqrt(3)R30 ordered pattern obtained in LEED measurements[3].

We report helium atom scattering (HAS) measurements of the structure and dynamics of the first H₂O layer on Au(111).  HAS is an extremely non-perturbative technique for studying surface structure and dynamics. It is sensitive to light atoms (e.g. the proton order in a water layer) and is capable of measuring the average structure on an atomic scale even in the presence of significant motion. Our measurements, performed at 110K, show a clear sqrt(3)xsqrt(3)R30  helium diffraction pattern which continuously intensifies during the exposure to H₂O,  suggesting the gradual formation of highly ordered H₂O islands which are commensurate with the underlying gold surface. Interference measurements were performed to measure the height of the water layer, the results are consistent with a unique “double bi-layer” structure suggested for this system[2] .

 [1] N. Ikemiya et al., J. Am. Chem. Soc. 119, 9919 (1997).

 [2] D. Stacchiola et al. J. Phys. Chem. C 113, 15102 (2009).

 [3] G. Pirug et al., Surf. Sci., 405, 87 (1998).