Ordered H2O Structures on a Weakly Interacting Surface: A Helium Diffraction Study of H2O/Au(111)

In this manuscript we report helium atom scattering (HAS) measurements of the structure of the first H2O layer on Au(111). The interaction between H2O and Au(111) is believed to be particularly weak, and conflicting evidence from several indirect studies has suggested that water either grows as 3D ice crystals or as an amorphous wetting layer. In contrast, our measurements show that between 110 and 130 K, H2O grows as highly commensurate well-ordered islands that only partially wet the gold surface. The islands produce a clear (√3 × √3)R30° diffraction pattern and are characterized by a well-defined height of ∼5 A with respect to the surface gold atoms. These findings provide support for a unique “double bi-layer” model, which has recently been suggested for this surface.