APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011;
Dallas, Texas
Abstract: T41.00001 : Deciphering the morphology of ice films on metal surfaces
2:30 PM–3:06 PM
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Author:
Although extensive research has been aimed at the structure of
ice films
[1], questions regarding basic processes that govern film
evolution remain.
Recently we discovered how ice films as many as 30 molecular
layers thick
can be imaged with STM [2]. The observed morphology yields new
insights
about water-solid interactions and how they affect the structure
of ice
films. This talk gives an overview of this progress for
crystalline ice
films on Pt(111) [2-5]. STM reveals a first molecular water layer
very
different from bulk ice: besides the usual hexagons it also contains
pentagons and heptagons [3]. Slightly thicker films ($\sim $1nm, at
T$>$120K) are comprised of $\sim $3nm-high crystallites,
surrounded by the
one-molecule-thick wetting layer. These crystals dewet by
nucleating layers
on their top facets [4]. Measurements of the nucleation rate as a
function
of crystal height provide estimates of the energy of the ice-Pt
interface.
For T$>$115K surface diffusion is fast enough that surface
smoothing and
2D-island ripening is observable [5]. By quantifying the T-dependent
ripening of island arrays we determined the activation energy for
surface
self-diffusion. The shape of these 2D islands varies strongly
with film
thickness. We attribute this to a transition from polarized ice
at the
substrate towards proton disorder at larger film thicknesses.
Despite fast
surface diffusion ice multilayers are often far from equilibrium.
For
example, ice grows between $\sim $120 and $\sim $160 K in its
cubic variant
rather than in its equilibrium hexagonal form. We found this to be a
consequence of the mismatch in the atomic Pt-step height and the
ice-bilayer
separation and propose a mechanism of cubic-ice formation via
growth spirals
around screw dislocations [2].
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[1] A. Hodgson and S. Haq, Surf. Sci. Rep. 64, 381 (2009).
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[2] K. Th\"{u}rmer and N. C. Bartelt, Phys. Rev. B 77, 195425
(2008).
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[3] S. Nie, P. J. Feibelman, N. C. Bartelt and K. Th\"{u}rmer,
Phys. Rev. Lett. 105, 026102 (2010).
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[4] K. Th\"{u}rmer and N. C. Bartelt, Phys. Rev. Lett. 100,
186101 (2008).
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[5] S. Nie, N. C. Bartelt, and K. Th\"{u}rmer, Phys. Rev. Lett.
102, 136101 (2009).
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.MAR.T41.1