2.3 Quantized Conductance Using Point Contact
The gap-type atomic switches that operate by controlling local ion migration and
solid electrochemical reaction in the electron and ion mixed conductor not only have
resistance switching but also interesting physical properties and functions such as
quantized conduction at room temperature [1, 11]. The quantized conductance was
observed when Ag atom cluster is slowly grown and shrunk between the Ag 2 S-STM
tip and the Pt substrate by applying relatively small voltage near the threshold
voltage to start the electrochemical reactions (Ag
+
(Ag2S) + e
À
⇆ Ag (cluster) ). The
experimental situation is the same as that in Fig. 3. Quantized conductance appeared,
as shown in Fig. 7a, by controlling the point contact between the Ag cluster on the
Ag 2 S tip and the Pt substrate. The time on the horizontal axis, in this figure, starts just
before the disappearance of the point contact between the Ag cluster and the Pt
substrate. The quantized conductance of the vertical axis is indicated by the number
of quantized unit, as calculated by dividing the electrical conductance by 2e
2 /h
(where e is the charge of an electron and h is Plank’s constant). By continuing to
apply a positive voltage of 19 mV to the Pt substrate, the appeared quantum
conductance decreased from 6 to 1 in steps, while decreasing the point contact
area between the Ag cluster and the Pt substrate. Subsequently the polarity of
applying voltage was switched to negative, and À29 mV was applied. The Ag
cluster regrew and formed the point contact. By increasing the area of the point
contact, the quantum number increased from 1 to 5 in steps again. Interestingly, it
was found that this quantized state can be controlled by applying a pulsed voltage to
the Ag 2 S-STM tip. In Fig. 7b, the state of the point contact whose quantum number
is 1 was formed between the STM tip and the substrate in advance. Next, when
voltages of 50 mV and À50 mV were applied to the substrate in pulses, the quantum
Fig. 7 (a) Phenomenon of quantized conductance by precisely controlling the point contact
between Ag cluster filament and Pt substrate [11]. (b) The switching between quantized conductance states by applying alternating positive and negative pulse voltages
8
K. Terabe et al.
The gap-type atomic switches that operate by controlling local ion migration and
solid electrochemical reaction in the electron and ion mixed conductor not only have
resistance switching but also interesting physical properties and functions such as
quantized conduction at room temperature [1, 11]. The quantized conductance was
observed when Ag atom cluster is slowly grown and shrunk between the Ag 2 S-STM
tip and the Pt substrate by applying relatively small voltage near the threshold
voltage to start the electrochemical reactions (Ag
+
(Ag2S) + e
À
⇆ Ag (cluster) ). The
experimental situation is the same as that in Fig. 3. Quantized conductance appeared,
as shown in Fig. 7a, by controlling the point contact between the Ag cluster on the
Ag 2 S tip and the Pt substrate. The time on the horizontal axis, in this figure, starts just
before the disappearance of the point contact between the Ag cluster and the Pt
substrate. The quantized conductance of the vertical axis is indicated by the number
of quantized unit, as calculated by dividing the electrical conductance by 2e
2 /h
(where e is the charge of an electron and h is Plank’s constant). By continuing to
apply a positive voltage of 19 mV to the Pt substrate, the appeared quantum
conductance decreased from 6 to 1 in steps, while decreasing the point contact
area between the Ag cluster and the Pt substrate. Subsequently the polarity of
applying voltage was switched to negative, and À29 mV was applied. The Ag
cluster regrew and formed the point contact. By increasing the area of the point
contact, the quantum number increased from 1 to 5 in steps again. Interestingly, it
was found that this quantized state can be controlled by applying a pulsed voltage to
the Ag 2 S-STM tip. In Fig. 7b, the state of the point contact whose quantum number
is 1 was formed between the STM tip and the substrate in advance. Next, when
voltages of 50 mV and À50 mV were applied to the substrate in pulses, the quantum
Fig. 7 (a) Phenomenon of quantized conductance by precisely controlling the point contact
between Ag cluster filament and Pt substrate [11]. (b) The switching between quantized conductance states by applying alternating positive and negative pulse voltages
8
K. Terabe et al.