Chemistry Reference
In-Depth Information
Fig. 7.7 Quenching of the tunneling switching of an OH. a-c Sequential STM images. a The
water molecule is moved to the vicinity of the OH situated on the bottom-right. b The paired
depression of the OH becomes single depression localized on the side of the water molecule.
c The paired depression is resumed after the water molecule is removed. The STM images were
acquired at V
s
= 24 mV and I
t
= 0.5 nA. d Schematic illustration of the quenching process.
e Schematic potential for the hydrogen without (left) and with (right) the perturbation
quenching of the switching takes place when a water molecule comes close to a
hydroxyl. Figure
7.7
shows the sequential STM images of the quenching. The
water molecule is manipulated to the vicinity of the hydroxyl located on the
bottom-right (Fig.
7.7
a). They are separated along [001] direction by 2b
0
(two
atomic rows). After the water manipulation the paired depression of the hydroxyl
is changed into the single depression localized on the side of the water molecule
(Fig.
7.7
b), while the other hydroxyl is still observed as a paired depression. The
paired depression is recovered when the water molecule is removed (Fig.
7.7
c).
The expected O-O distance of *7.4 Å between the water and hydroxyl is not
likely to be H-bond interaction. Thus it is assumed that the long-range interaction,
such as dipole-dipole or substrate mediated interaction, works between them and
consequently the potential of the switching is perturbed.
It is noted that the low-current state is substantially live longer in Fig.
7.5
b.
This indicates that OD prefers the orientation pointing away from the tip. It is
assumed that substantial perturbation which stabilizes such an orientation exists
between the tip and molecule, which is expected to be varied through changing the
relative distance between the tip and molecule. Indeed, at lower current conditions,
