| Abstract:
Recently we have discovered a way to use STM to image the morphology of thin ice films [1], despite the fact that ice is a good electrical insulator. The observed morphology has given new insights about what determines the structure of ice films and, in particular, about water-solid interactions. In this talk, I will overview this progress for ice films on Pt(111) [1-4]. I will discuss the structure of the first molecular water layer, showing that the hydrogen-bonding network is very different from bulk ice [2]. Small multilayer crystals of ice dewet from the Pt: we observe them to grow in height by the nucleation of new layers. Measurements of the nucleation rate as a function of height provide and estimate of the energy of the ice-Pt interface [3]. For T > 110K surface diffusion is fast enough that surface smoothing and 2-D island ripening is observable, giving information about the nature of admolecules on the ice surface [3]. Despite fast surface diffusion, the structure of the small ice crystals can be far from equilibrium. For example, cubic ice rather than the usual hexagonal ice is often observed. We attribute the fast growth of cubic ice to the spirals forming around threading screw dislocations that are generated during island coalescence [1]. By monitoring the shape of two-dimensional islands on top of ice films of various thicknesses we find evidence that the mechanisms of ice growth induces order in the hydrogen-bonding network. This work was supported by the Office of Basic Energy Sciences, Division of Materials Sciences, U. S. Department of Energy under Contract No. DE-AC04-94AL85000.
Joint work with S. Nie, and K. Thürmer
Sandia National Laboratories, Livermore, California.
[1] K. Thürmer and N.C. Bartelt, Phys. Rev. B 77, 195425 (2008).
[2] S. Nie, P.J. Feibelman, N.C. Bartelt and K. Thürmer, Phys. Rev. Lett. 105, 026102 (2010).
[3] K. Thürmer and N.C. Bartelt, Phys. Rev. Lett. 100, 186102 (2008).
[4] S. Nie, N.C. Bartelt, K. Thürmer, Phys. Rev. Lett. 102, 136102 (2009). |
