  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.
