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J. Balajka, J. Pavelec, M. Komora, M. Schmid, U. Diebold:
"Apparatus for dosing liquid water in ultrahigh vacuum";
Review of Scientific Instruments, 89 (2018), 0839061 - 0839066.

The structure of the solid-liquid interface often defines the function and performance of materials in
applications. To study this interface at the atomic scale, we extended an ultrahigh vacuum (UHV)
surface-science chamber with an apparatus that allows bringing a surface in contact with ultrapure
liquid water without exposure to air. In this process, a sample, typically a single crystal prepared and
characterized in UHV, is transferred into a separate, small chamber. This chamber already contains a
volume of ultrapure water ice. The ice is at cryogenic temperature, which reduces its vapor pressure
to the UHV range. Upon warming, the ice melts and forms a liquid droplet, which is deposited on the
sample. In test experiments, a rutile TiO2(110) single crystal exposed to liquid water showed unprecedented
surface purity, as established by X-ray photoelectron spectroscopy and scanning tunneling
microscopy. These results enabled us to separate the effect of pure water from the effect of low-level
impurities present in the air. Other possible uses of the setup are discussed.