polarity of V s and magnitude of I t were changed, in which V s and I t are the bias
voltage applying to the substrate and the tunneling current, respectively. The conditions of V s and I t were changed in the order of 1, 2, 1, 3, 4, and 3 conditions, and
this series of operation was repeated three times in Fig. 2. No Ag cluster growth was
observed at V s ¼ À2.0 V and I t ¼ 0.05 nA (condition 1). However, when I t was
increased to 1.35 nA with V s kept constant (condition 2), the Ag cluster started to
grow at the apex of the Ag 2 S tip at a growth rate of about 0.1–0.2 nm/s. The growth
stopped by returning the condition from 2 to 1. No change was observed in the
grown cluster by the polarity switching of V s from negative to positive, with keeping
I t at the same (condition 3). However, when I t was increased to 0.35 nA (condition 4),
200
150
100
50
0
8000
6000
4000
2000
0
1: Vs= -2.0V It=0.05nA
2: Vs= -2.0V It=1.35nA
3: Vs=+2.0V It=0.05nA
4: Vs=+2.0V It=0.35nA
1
1
1
1
1
1
3
3
3
3
3
3
2
2
2
4
4
4
Change of t ip height (nm)
Time (sec.)
-
+
sample
Ag cluster
Ag
Ag2S
Sample bias
Fig. 2 Reversible growth and shrinkage of Ag cluster on the Ag 2 S-STM tip by changing the
condition of applied bias voltage. [9] © (2002), AIP publishing LLC
Invention and Development of the Atomic Switch
3