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

Abstract

KEYWORDS : Surface structure, water adsorption on metals, water gold interaction, helium atom scattering.! " ! 1 ABSTRACT: 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 wellordered islands which only partially wet the gold surface. The islands produce a clear diffraction pattern and are characterized by a well defined height of ~ 5Å 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. ! ! Introduction:!In recent decades, numerous experimental and theoretical studies have been devoted to understanding the interaction of H2O with metallic surfaces 1-3 . This ongoing activity can be related to numerous technological applications, and the significant experimental and theoretical challenges encountered when studying these delicate and complex surface systems. In particular, the sensitivity of H2O molecules to electrons and radiation, the strong dependency of the observed structures on the exact preparation conditions and the difficulties encountered in theoretical studies have lead to conflicting results and controversy 1, 2, 4, 5 . ! An experimental method which played a leading role in determining the structure of water layers on metal surfaces is Low Energy Electron Diffraction (LEED) 1, 2 . While this technique has and is still supplying valuable information, it has a few limitations, in particular the sensitivity of " ! AUTHOR INFORMATION!

Motion of water monomers reveals a kinetic barrier to ice nucleation on graphene

“…Simultaneously, diffraction peaks emerge at the positions of a graphene lattice, as shown by the red curve in Fig. 2 d. The relative diffraction intensities are identical to the pristine graphene surface (grey dashed curve), which would not be the case for a crystalline ice overlayer 32 . Ice I h and ice I c also have too large a lattice spacing 33 to give rise to this periodicity, even for the spacing in the recently discovered square ice 33 , 34 .…”

Material properties particularly suited to be measured with helium scattering: selected examples from 2D materials, van der Waals heterostructures, glassy materials, catalytic substrates, topological insulators and superconducting radio frequency materials

“…Due to the large cross section of HAS to isolated adsorbates (including hydrogen as described in Section 3.5), the position and structure of hydrogen atoms and adsorbed water layers can be readily determined. [103][104][105] These include also the hydrogenation of a graphene surface 106 while H-positions are hard to determine with other methods (e.g., hydrogen is a weak scatterer for electrons) which also present a severe risk of damaging the H-layer. 107 In a study of highly proton-ordered water structures on oxygen pre-covered Ru(0001) it could be shown that the atomic oxygen and the oxygen from water form a (2 Â 2) surface reconstruction, which however, is broken by the hydrogen to give a (2 Â 4) surface reconstruction: while LEED measured a (2 Â 2), HAS measured a (2 Â 4) superstructure.…”

Transfer-matrix theory of surface spin-echo experiments with molecules

“…When used to study surfaces, HeSE experiments can be classified as a subset of quasi-elastic helium atom scattering experiments [26]. Surface-sensitive HeSE experiments [31][32][33] have been used to study surface morphology [36], molecular and atomic surface diffusion [32,33,[37][38][39][40][41], inter-adsorbate forces [38,42], phonon dispersions [32,33,43], phason dispersions [44], structures and phase transitions of ionic liquids [45] and friction between adsorbates and surfaces [46][47][48]. HeSE experiments have provided information about potential energy surfaces [32,33,49] and surface-adsorbate interactions [32,33,50] and are frequently combined with microscopic calculations to both test theory and gain insight into surface-adsorbate interactions [39,51,52].…”