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 110K and 130K, H2O grows as highly commensurate well ordered islands which only partially wet the gold surface. The islands produce a clear (sqrt3Xsqrt3)R30 diffraction pattern and are characterized by a well defined height of ~ 5 Angstrom with respect to the surface gold atoms. These findings provide support for a unique double bilayer model which has recently been suggested for this surface.