Chemistry Reference
In-Depth Information
Fig. 6.10 STM images of various clusters spontaneously formed at *30 K. The image was
acquired at 6 K. The identified clusters are labeled with their constituent numbers. The majority
species of trimer is a [110]-chain. The meta-stable trimer (labeled with 3
0
) in the bottom left was
mobile and appeared fractional. Tetramer is most likely observed in the cyclic form (labeled with
4
0
). The range of the height shown in the color bar is from -0.2 to 1.3 Å. The image was obtained
at V
s
= 24 mV and I
t
= 0.5 nA, and the scan size is 170 9 170 Å
2
open question because H atoms were invisible with x-ray. A chain configuration is
not converted into the other configurations spontaneously at low bias conditions,
suggesting that it is sufficiently stable. It would appear that an anisotropic atom
arrangement of Cu(110) allows water molecules to arrange one-dimensionally
despite the reduction of the number of H bond.
The temperature dependence of clustering behavior provides us with insights of
the thermodynamics. As the temperature increases, water molecules readily diffuse
and aggregate spontaneously to form a variety of clusters. Figure
6.10
is a typical
STM image after the surface is heated up to *30 K. Most of the clusters can be
identified and the cluster size is labeled in the image. A trimer and tetramer are
observed mainly as a [110]-chain and cyclic form, respectively, suggesting that
they are thermodynamically favorable among several isomeric structures. Also
longer chains as well as unidentified larger clusters are observed. It is clear that the
trimer is the most predominant species, indicating that the diffusion of the trimer is
still restricted at 30 K.
