Water Diffusion and Clustering on Pd(111)

Abstract

The adsorption, diffusion, and clustering of water molecules on a Pd(111) surface were studied by scanning tunneling microscopy. At 40 kelvin, low-coverage water adsorbs in the form of isolated molecules, which diffuse by hopping to nearest neighbor sites. Upon collision, they form first dimers, then trimers, tetramers, and so on. The mobility of these species increased by several orders of magnitude when dimers, trimers, and tetramers formed, and decreased again when the cluster contained five or more molecules. Cyclic hexamers were found to be particularly stable. They grow with further exposure to form a commensurate hexagonal honeycomb structure relative to the Pd(111) substrate. These observations illustrate the change in relative strength between intermolecular hydrogen bonds and molecule-substrate bonds as a function of water cluster size, the key property that determines the wetting properties of materials.

Decisive role of nuclear quantum effects on surface mediated water dissociation at finite temperature

“…Moreover, the structural, dynamic, and electronic properties of water are known to be heavily affected by the quantum nature of the nuclei even at room temperature [7][8][9][10][11][12][13][14] . In fact, nuclear quantum effects (NQE) have also been shown, through several experiments and a few theoretical works, to play a crucial role in the behaviour of organic adsorbates on metallic surfaces [15][16][17][18][19][20][21][22][23][24] . It is thus to be expected that both conformational entropy and nuclear quantum contributions impact the physics underlying the processes of water adsorption and dissociation on metallic surfaces.…”

The interplay between apparent viscosity and wettability in nanoconfined water

“…Interfacial and nanoconfined liquid flow is relevant for biology 2,3 , tribology 4 , nanofluidics and high-resolution three-dimensional, two-dimensional printing 5 . Confined fluids exhibit unique structural, dynamical, electrokinetic and mechanical properties that are different from those of the bulk [6][7][8][9][10] . It is now well-known that liquids confined between surfaces, especially at gaps below a few nanometres, can present a dramatic increase in their viscosity 6,7,11,12 .…”

An unconventional bilayer ice structure on a NaCl(001) film

“…This hexagonal ice-like bilayer consists of a puckered hexagonal overlayer with water molecules located at two distinct heights, where the lower water molecules donate two hydrogen bonds (H bonds) to the upper layer and bond relatively strongly with the substrate, whereas the higher-lying molecules provide one donor H bond to the bottom layer and do not interact appreciably with the substrate. Recent molecular-level studies on water/metal interfaces reveal that water is distorted from the conventional bilayer-like arrangement and exhibits remarkably rich H-bonded structures arising from a subtle balance between the water-water and water-metal interactions [2][3][4][5][6][7][8][9][10][11][12][13] . Therefore, the validity of the hexagonal bilayer model on interfacial water is being challenged 13 .…”