162
4 Toward More Sophisticated Problems
0
0.5
1
1.5
2
-1
-0.5
0
0.5
1
1
2
3
4
(a)
0
0.5
1
1.5
2
-1
-0.5
0
0.5
1
(b)
0.2
Fig. 4.10 Transmission spectra T (ε) of a CNT and b H-CNT. The triangular area shown in red
between the broken lines indicates the bias window. Adapted by permission from Fueno et al.
(2012). Copyright (2012)
(b)
(c)
(a)
Fig. 4.11 Unoccupied orbital patterns with the energies of a −0.01 and b 0.01 eV contributing I sd
at V sd = 0.2 V for CNT and of c 0.63 eV at V sd = 1.6 V for H-CNT. Adapted by permission from
Fueno et al. (2012). Copyright (2012)
b have the orbital energies of −0.01 and 0.01 eV, respectively. These are delocalized over the central region and contribute to electric current at V sd = 0.2 V.
On the other hand, as to H-CNT, it is seen in Fig. 4.11c that the unoccupied
orbital whose energy is 0.63 eV is confined in the Z H region under the condition
of V sd = 1.6 V. It is thus understood that the Z H region behaves as a quantum
well for H-CNT.
(4) Fig. 4.12 shows the gate voltage (V g ) dependencies of I sd −V sd characteristics.
Note that the orbital energy level in the quantum dot region can be controlled by
applying V g . It is seen that in Fig. 4.12a for CNT the change in V g does not give
remarkable effect to the I sd −V sd characteristics, since there is no quantum dot
in the simple CNT. On the other hand for H-CNT, the I sd −V sd characteristics
show typical oscillation tendency and increase in the number of peaks upon
the change in V g as seen in Fig. 4.12b. This obviously signifies the resonant
tunneling in which the orbital energy levels are made to match with those of the
outer wire portions by changing V g .
It should be pointed out that I sd in CNT is obviously large (100 μA order) in spite
of a single molecular wire, which comes from the overestimation of the transmission
4 Toward More Sophisticated Problems
0
0.5
1
1.5
2
-1
-0.5
0
0.5
1
1
2
3
4
(a)
0
0.5
1
1.5
2
-1
-0.5
0
0.5
1
(b)
0.2
Fig. 4.10 Transmission spectra T (ε) of a CNT and b H-CNT. The triangular area shown in red
between the broken lines indicates the bias window. Adapted by permission from Fueno et al.
(2012). Copyright (2012)
(b)
(c)
(a)
Fig. 4.11 Unoccupied orbital patterns with the energies of a −0.01 and b 0.01 eV contributing I sd
at V sd = 0.2 V for CNT and of c 0.63 eV at V sd = 1.6 V for H-CNT. Adapted by permission from
Fueno et al. (2012). Copyright (2012)
b have the orbital energies of −0.01 and 0.01 eV, respectively. These are delocalized over the central region and contribute to electric current at V sd = 0.2 V.
On the other hand, as to H-CNT, it is seen in Fig. 4.11c that the unoccupied
orbital whose energy is 0.63 eV is confined in the Z H region under the condition
of V sd = 1.6 V. It is thus understood that the Z H region behaves as a quantum
well for H-CNT.
(4) Fig. 4.12 shows the gate voltage (V g ) dependencies of I sd −V sd characteristics.
Note that the orbital energy level in the quantum dot region can be controlled by
applying V g . It is seen that in Fig. 4.12a for CNT the change in V g does not give
remarkable effect to the I sd −V sd characteristics, since there is no quantum dot
in the simple CNT. On the other hand for H-CNT, the I sd −V sd characteristics
show typical oscillation tendency and increase in the number of peaks upon
the change in V g as seen in Fig. 4.12b. This obviously signifies the resonant
tunneling in which the orbital energy levels are made to match with those of the
outer wire portions by changing V g .
It should be pointed out that I sd in CNT is obviously large (100 μA order) in spite
of a single molecular wire, which comes from the overestimation of the transmission