AVS 49th International Symposium
    Surface Science Tuesday Sessions
       Session SS2-TuM

Paper SS2-TuM5
Water Diffusion and Clustering on Pd(111)

Tuesday, November 5, 2002, 9:40 am, Room C-110

Session: Diffusion & Growth on Metal Surfaces
Presenter: T. Mitsui, Lawrence Berkeley National Laboratory
Authors: T. Mitsui, Lawrence Berkeley National Laboratory
M.K. Rose, University of California
E. Fomin, University of California
F. Ogletree, Lawrence Berkeley National Laboratory
M. Salmeron, Lawrence Berkeley National Laboratory
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The adsorption, diffusion and the formation of clusters of water molecules on Pd(111) has been studied by scanning tunneling microscopy. Water adsorbs in the form of isolated molecules at 40 K. With the help of STM movies of the molecular random walk and of atom-tracking techniques we studied the process of diffusion and cluster formation. When two water molecules meet they form a dimer, then a trimer and so on. The mobility of dimers and trimers was found to be nearly three orders of magnitude larger than that of single molecules. Pentamers and larger clusters are immobile at 40 K, although changes in their conformation were observed. Hexamers with a cyclic configuration are particularly stable. They grow with further coverage forming a commensurate hexagonal honeycomb with (@sr@3x@sr@3)R30° structure relative to the Pd(111) substrate.