APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011;
Dallas, Texas
Session T41: Focus Session: The Role of Water in Energy Production and Utilization I
2:30 PM–5:30 PM,
Wednesday, March 23, 2011
Room: A115/117
Sponsoring
Unit:
DCP
Chair: Greg Kimmel, Pacific Northwest National Laboratories
Abstract ID: BAPS.2011.MAR.T41.1
Abstract: T41.00001 : Deciphering the morphology of ice films on metal surfaces*
2:30 PM–3:06 PM
Preview Abstract
Abstract
Author:
Konrad Th\"{u}rmer
(Sandia National Laboratories, CA)
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).
*Joint work with N.C. Bartelt and S. Nie, Sandia Natl. Labs, CA. This work was supported by the Office of Basic Energy Sciences, Division of Materials Sciences, U.S. DOE under Contracts No. DEAC04-94AL85000.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.MAR.T41.1