Noncontact Atomic Force Microscopy - Yale School of Engineering ...

One and Two Dimensional Structure of Water on Cu(110) and
O/Cu(110)-(2x1) Surface
Byoung Y. Choi 1 , Yu Shi 1,2 , Thomas Duden 3 , and Miquel Salmeron 1,2
1 Material Science Division, Lawrence Berkeley National Laboratory, Berkeley, USA
2 Department of Materials Science and Engineering, University of California, Berkeley, USA
3 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, USA.
P.II-03
The interaction of water on metal surfaces like Ru, Pt, or Pd has been studied for a long
time to understand its role in catalysis, electrochemistry and environmental science.
Especially, the structure of water on atomically clean surfaces has been an important
subject because of its complexity. Water molecules can easily diffuse and aggregate on
the surface at over ~40K to form a two dimensional (2D) hexagonal structure on closepacked
metallic surfaces [1] .
For water on Cu, it has been reported that it forms 1D-like chains at low coverage on
the (110) surface while it forms 2D hexagonal networks at higher coverage. It has been
proposed that this 1D wire is built from hydrogen bonded hexagons as building blocks
[2]. The 1D chain structure was recently suggested to be a combination of pentagons
based on experiment and theory [3]. An important question is how the pentagon based
chains evolve into hexagon based 2D networks. To determine this, more careful
investigation at the atomic scale is required.
Atomic force microscopy (AFM) in non-contact (NC) mode can be used to study the
molecules on metals and insulators with atomic resolution. We built a tuning fork base
NC-AFM which works in both 4K and 77K with a FET type current amplifier on the low
temperature side to reduce a noise coupling through the signal lines. Our instrument can
work in either the NC-AFM or STM mode, which provides complementary information
and is useful for reference and calibration.
With this instrument we investigated the evolution of water from 1D chain to 2D
network on clean and oxygen precovered Cu(110) surfaces at low temperature, which
reveals the growth mechanism of water at various coverages and growth temperatures.
By dosing water on partially covered O/Cu(110)-(2x1) surface, we were able to show that
the oxygen atoms at the edges of CuO rows play an important role in forming well
ordered 2D hexagonal networks even at low coverage. Finally we suggest that water
hexamer can be a base structure of both 1D and 2D islands when it grows adjacent to
CuO row.
[1] Angelos Michaelides and Karina Morgenstern, Nature Mater. 6, 597 (2007).
[2] T. Yamada, S. Tamamori, H. Okuyama, and T. Aruga, Phys. Rev. Lett. 96, 036105 (2006)
[3] Javier Carrasco, Angelos Michaelides, Matthew Forster, Sam Haq, Rasmita Raval and Andrew
Hodgson, Nature Mater. doi:10.1038/nmat2403 (2009).
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