H₂O on Pt(111): structure and stability of the first wetting layer

Abstract

We study the structure and stability of the first water layer on Pt(111) by variable-temperature scanning tunneling microscopy. We find that a high Pt step edge density considerably increases the long-range order of the equilibrium √37 × √37R25.3°- and √39 × √39R16.1°-superstructures, presumably due to the capability of step edges to trap residual adsorbates from the surface. Passivating the step edges with CO or preparing a flat metal surface leads to the formation of disordered structures, which still show the same structural elements as the ordered ones. Coadsorption of Xe and CO proves that the water layer covers the metal surface completely. Moreover, we determine the two-dimensional crystal structure of Xe on top of the chemisorbed water layer which exhibits an Xe-Xe distance close to the one in bulk Xe and a rotation angle of 90° between the close-packed directions of Xe and the close-packed directions of the underlying water layer. CO is shown to replace H(2)O on the Pt(111) surface as has been deduced previously. In addition, we demonstrate that tunneling of electrons into the antibonding state or from the bonding state of H(2)O leads to dissociation of the molecules and a corresponding reordering of the adlayer into a √3 × √3R30°-structure. Finally, a so far not understood restructuring of the adlayer by an increased tunneling current has been observed.

A unified study for water adsorption on metals: meaningful models from structural motifs

“…14 This sqrt(37) bilayer contained a rotated hexameric cycle made of flat lying water molecules in the center with 0.70 ML coverage. Other structures with the same patterns, like ffiffiffiffiffi 39 p  ffiffiffiffiffi 39 p À R16:1 , present a different rotation of the central hexagon, a coverage of 0.69 ML, and are metastable between 130 and 140 K. 15 For Pd(111), adsorption experiments in the sub-monolayer coverage regime (0.5 ML) identified two patterns: Rosette and Lace. 16 While Rosettes behave as ''magic clusters'' and are isolated on the surface, Fig.…”

Solvation and Reaction of Ammonia in Molecularly Thin Water Films

“…5 In addition to these two energetically favored structures, water can form a (√3 × √3)R30°structure (R3 structure), which is 0.1 eV/molecule less stable than the R37 structure. 5 Mixed water−hydroxyl films, formed by coadsorption of H 2 O and O atoms 19 or by electron injection after prolonged scanning in an STM experiment, 32 were reported to exhibit (√3 × √3)R30°geometry. In the present case, however, the clean substrate was recovered after annealing to 160 K, indicating that the H 2 O molecules were intact, 19 forming an array of hexagons resembling a flattened bilayer of the basal plane of hexagonal I h ice.…”

Growth and Structure of the First Layers of Ice on Ru(0001) and Pt(111)

“…21 As we show next, crystalline island growth occurs only on the √3 water monolayer on Pt(111). 30,31…”