Chemistry Reference
In-Depth Information
Fig. 10.4 Sequential STM images during the assembly process of an H
2
O-(OH)
4
complex from
two oxygen atoms and three water molecules, along with the schematic illustration of the
reactions. a Two oxygen atoms are adsorbed along the [001] direction with the interatomic
distance of 2b
0
. The two white dots indicate the hollow sites to which the oxygen atoms are
adsorbed. b A water molecule is manipulated toward one oxygen atom to yield (OH)
2
? O. c A
second water molecule reacted with another oxygen atom to yield (OH)
4
. d Finally, a third water
molecule was attached to the end of (OH)
4
, resulting in a H
2
O-(OH)
4
chain complex. The dots in
c and (d) indicate the short-bridge sites occupied by oxygen atoms, although they are displaced
from the exact short-bridge sites. The images were recorded at V
s
= 30 mV and I
t
= 0.2 nA for
(a-c) and I
t
= 0.5 nA for (d). The image size is (23 9 29 Å
2
). The color bar corresponds to the
topographic height from -0.46 Å (low) to 0.35 Å (high)
10.2.3 Direct Observation of Hydrogen-Atom Relay Reactions
A voltage pulse with the STM over a water molecule induces the flip of the chain-
complex. The flip can be observed in a series of the chain complexes (Fig.
10.7
b-
d). By comparison to the calculated structure and the STM simulation, it is obvious
that the flip corresponds to the H-atom relay reaction and the water molecule is
structurally-transferred from the end of the chain to another (Fig.
10.7
a).
According to the detailed analysis of the STM image, the binding site of the
oxygen atoms in the complex is not altered before and after the flip, suggesting the
migration of the constituent molecules to the other site is not included. Thus only
the H-atom relay is merely involved in the process.
