Chemistry Reference
In-Depth Information
Fig. 8.8 Schematic model describing the mechanism for the non-linear I-V characteristics of a
hydroxyl dimer on Cu(110). a The STM tip is fixed over the depression (low conductance state)
before ramping up the bias voltage. b When the dimer is flipped, the appearance under the tip
becomes brighter than (a). (high conductance state). c Before the vibrational excitation the
occupation of the low conductance state is dominant. d After the excitation the switching is
dramatically enhanced, resulting in the reduction (increase) of the occupation of the high (low)
conductance state. e In this model the stepwise change is predicted at the vibration energy
Fig. 8.9 The IETS (d
2
I/dV
2
) spectra (solid lines) and the fractional occupations for an (OD)
2
(open squares) and (OH)
2
(open circles). The peak and dip voltages in the spectra were
determined by fitting the data to the derivative of Gaussian function. The spectra were obtained
with the STM tip fixed over the depression at the set point of I
t
= 0.5 and 5 nA at V
s
= 24 mV
for an (OH)
2
and (OD)
2
, respectively. An (OH)
2
would be broken during the measurement with
the set point of 5 nA. The modulation voltage of V
rms
= 6 mV with the frequency of 590 Hz was
used for d
2
I/dV
2
measurement. The fractional occupations were also measured with the STM tip
fixed over the depression at the set point of I
t
= 0.05 and V
s
= 24 mV for an (OH)
2
and (OD)
2
between two orientations can be induced by the vibrational excitation, while
tunneling process is quenched because of the H-bond formation as well as the mass
