Chemistry Reference
In-Depth Information
Fig. 3.1
a Schematic illustration of the LT-STM system. b Overview picture of the LT-STM
and He, respectively. The STM head is cooled by the contact to the Cu block on the
bottom of the inner cryostat. During the measurement, the STM head is suspended
by springs for the vibrational isolation. Cu bundles were used to connect parts of the
head for a rapid thermal equilibrium. The vacuum system consists of sputter ion
pumps, Ti sublimation pumps, a turbo molecular pump and a rotary pump. UHV
conditions can be obtained by baking the chamber for 3 or 4 days at *400 K, and
are kept using ion pumps and titanium sublimation pumps. The cryostat in the STM
chamber also works as a cryo-pump. STM measurements were conducted below
5 9 10
-11
Torr. In this vacuum the contamination of surfaces can be avoided
during the experimental time scale.
3.2 Sample Preparation
A Cu(110) surface was cleaned by repeated cycles of Ar
+
sputtering and annealing
up to *800 K under UHV conditions to get an atomically clean surface. Ion
sputtering is a conventional and effective cleaning method of metal surfaces [
1
-
3
].
Since the ion bombardment causes the degradation of the surface structure, sub-
sequent annealing is essential to restore the crystalline surface and eliminate
embedded and adsorbed Ar atoms. Figure
3.2
shows a high-resolution STM image
of the clean Cu(110) surface that has an anisotropic arrangement as illustrated in
the STM image. Cu atomic rows run along the
½
110
direction. The quasi 1-D
geometory makes the dynamics of molecules anisotropic, giving rise to unique
directional growth of water layers [
4
-
9
].
In order to obtain isolated single water molecules, the surface was exposed to
high-purely H
2
OorD
2
O gases below 20 K via a tube doser positioned *1cm
apart from the surface. The exposure amount was controlled using a leak valve.
