Chemistry Reference
In-Depth Information
Fig. 8.6 A typical averaged
I-V curve (dashed red curve)
accumulated 60 times and dI/
dV spectra (solid blue curve)
obtained over the depression
of (OD)
2
at the set point of
I
t
= 5 nA and V
s
= 24 mV.
The modulation voltage of
V
rms
= 6 mV with the
frequency of 590 Hz was
used for the dI/
dV measurement
Fig. 8.7 a The fractional occupation (upper) and the state-resolved I-V plot (lower) for the low
(blue squares) and high (red crosses) current states as a function of the applied bias voltage
measured for (OD)
2
. The I-V plot reproduced by using these data is shown in b (blue circles) with
an averaged I-V curve (red line). These data were obtained at the set point of I
t
= 0.05 nA and
V
s
= 24 mV
attributed to the dynamical property of a dimer, that is, the change in the fractional
occupation of the two states caused by the m(OH(D)) excitation. Figure
8.8
shows
a schematic illustration of the mechanism. At the initial geometry the STM tip is
fixed over the depression of a dimer that corresponds to the low current state
(Fig.
8.8
a). Before the vibrational excitation, the occupation of the low current
state is dominant (Fig.
8.8
c). After the excitation, the enhancement of the
switching causes a significant change in the occupation; the low current and high
current states are decreased and increased, respectively (Fig.
8.8
d), eventually
giving rise to the increase of the average current. Furthermore, the d
2
I/dV
2
spectra
(Fig.
8.9
) are characterized by the peak and the subsequent dip which correspond
to the onset and saturation of the occupation changes, respectively.
8.3 Summary
A hydroxyl dimer on Cu(110) is produced by the reaction of a water molecule with
an oxygen atom. Hydroxyl groups adsorb on the twofold short-bridge site and is
titled along the [001] direction in common with the monomer. The switching
