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Electrical Switching in Carbon Nanotubes and Conformational Transformation of Chain Molecules. 2006. 8. 30. Jisoon Ihm School of Physics, Seoul National University. Collaborators. Sangbong Lee, Seungchul Kim, Byoung Wook Jeong (Seoul Nat’l Univ.)

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slide1

Electrical Switching in Carbon Nanotubes and Conformational Transformation of Chain Molecules

2006. 8. 30

Jisoon Ihm

School of Physics, Seoul National University

collaborators
Collaborators
  • Sangbong Lee, Seungchul Kim, Byoung Wook Jeong (Seoul Nat’l Univ.)
  • Young-Woo Son ,Marvin Cohen, Steven Louie (Berkeley)
slide4

Electronic Structure of Metallic Armchair Nanotube

Band structure of a (10,10) single-wall nanotube ( LDA, first-principles pseudopotential method )

slide5

CBM

VBM

slide7

Conductance with Boron Impurity

Similarity to acceptor states in semiconductors

A

A

H.J. Choi et al, PRL 84, 2917(2000)

slide8

Conductance with Nitrogen Impurity

Similarity to donor states in semiconductors

D

D

slide9

I. Electrical switching in metallic carbon nanotubes

( Y.-W. Son, J. Ihm, etc., Phys. Rev. Lett. 95, 216602(2005) )

slide10

1. Motivation

  • Metallic and semiconducting carbon nanotubes are produced simultaneously.

C. Dekker, A. Zettl

Selection Problem!

  • Semiconducting nanotubes : easy to change conductance using gate
  • Metallic nanotubes: robust against impurities, defects, or external fffffffff fields (difficult to change conductance)
slide11

1. Motivations – cont’d

Is it possible to control the conductance of metallic single-wall carbon nanotubes?

S.B. Lee, A. Zettl

Interplay between defects and electric fields

electron flow

slide12

2. Calculational Method

2

: Landauer formalism

SCattering-state appRoach for eLEctron Transport (SCARLET)

H. J. Choi et al, PRB 59, 2267(1999), and in preparation

slide13

Nitrogen Boron

The electronic potential of N(B) is lowered. Levels of quasibound states move down.

The electronic potential of N(B) is raised. Levels of quasibound states move up.

3. B(N) doped (10,10) SWNT

slide14

4. Switching in B-N codoped (10,10) SWNT

B

N

  • Switching behavior: off/on ratio=607kΩ/6.4kΩ~100
  • Maximum resistance depends on the relative position between N and B.
  • Asymmetric resistance w.r.t. the direction of Eext
slide15

5. Scaling for larger (n,n) SWNT

∆H ∝ Eext · (diameter)2

slide16

6. Switching in (10,10) SWNT with Vacancies

  • Four carbon atoms are removed (Strong repulsive potential).
  • Doubly degenerate quasibound states at fermi level
  • Switching behavior: off/on ratio=1200kΩ/6.4kΩ ~200
  • Symmetric resistance w.r.t. the direction of Eext
slide17

6. Switching in (10,10) with Vacancies – cont’d

Quasibound states move up or down depending on the direction of Eext.

summary
Summary
  • Conductance of metallic CNTs with impurities and applied electric fields is studied.
  • With N and B impurity atoms on opposite sides, asymmetric switching is possible using external fields.
  • With a large vacancy complex, symmetric switching is possible using external fields.
slide19

II. Conformational Transform of Azobenzene Molecules

( B.-Y. Choi et al., Phys. Rev. Lett. 96, 156106(2006) )

summary1
Summary
  • Electrical pulse is found to induce molecular flip between trans and cis structures.
example of material design total reflection by three nitrogen impurities

Appendix

Example of MATERIAL DESIGN : totalreflection by three nitrogen impurities

Importance of geometric symmetry (equilateral triangle)

Doubly degenerate impurity states cause perfect reflection at 0.6 eV.

(Both even and odd states are fully reflected at same energy.)

slide31

Difference between Eext and impurity potential U

Lippman-Schwinger formalism:

Eigenstate |ψ> of Htot associated with the eigenstate |> of H0 with the same energy E (with impurity potential U at site a)

slide32

Projection on to the impurity |>

where

Reflection for the specific state |> :

Total transmission :

Resonance condition :

slide33

Effect of Eext : Green’s function itself changes.

: G0 projected at site a

With applied electric fields,

Suppose ∆H at site α is ∆E.

In other words, is G0(α;E) shifted by ∆E.

changing e ext is different from changing u

(10,10) SWNT with NO Eext while changing the strength of the attractive potential, U.

EF

Changing Eext is different from changing U.

(10,10) SWNT with a single attractive impurity of U=-5|t| while changing Eext

power consumption of sed lcd pdp 36in
Power consumption of SED, LCD, PDP (36in)

Canon-Toshiba SED at CEATEC2004

SED

LCD

PDP

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