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Jisoon Ihm School of Physics, Seoul National University

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Jisoon Ihm School of Physics, Seoul National University

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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

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

Basics:Substitutional Impurity in Metallic Carbon Nanotubes

Boron or Nitrogen

Tube axis

Electronic Structure of Metallic Armchair Nanotube

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

CBM

VBM

Tube axis

Conductance with Boron Impurity

Similarity to acceptor states in semiconductors

A

A

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

Conductance with Nitrogen Impurity

Similarity to donor states in semiconductors

D

D

I. Electrical switching in metallic carbon nanotubes

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

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)

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

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

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

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

5. Scaling for larger (n,n) SWNT

∆H ∝ Eext · (diameter)2

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

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

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

- 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.

II. Conformational Transform of Azobenzene Molecules

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

Azobenzene (AB) : C6H5-N=N-C6H5

Transformation between transAB and cisAB

(Voltage bias using STM)

Geometries of tAB

Geometries of cAB

Optimal geometry of tAB and cAB

STS for tAB and cAB

Disperse Orange 3 (NH2-C6H4-N=N-C6H4-NO2)

Flat geometry of cAB

- Electrical pulse is found to induce molecular flip between trans and cis structures.

Appendix

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.)

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)

Projection on to the impurity |>

where

Reflection for the specific state |> :

Total transmission :

Resonance condition :

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.

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

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

EF

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

SAMSUNG SDI FED – 2005 -

Canon-Toshiba SED at CEATEC2004

SED

LCD

PDP