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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

Collaborators Transformation of Chain Molecules

- 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 Transformation of Chain Molecules

Boron or Nitrogen

Tube axis

Electronic Structure of Metallic Armchair Nanotube Transformation of Chain Molecules

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

CBM Transformation of Chain Molecules

VBM

Tube axis Transformation of Chain Molecules

Conductance with Boron Impurity Transformation of Chain Molecules

Similarity to acceptor states in semiconductors

A

A

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

Conductance with Nitrogen Impurity Transformation of Chain Molecules

Similarity to donor states in semiconductors

D

D

I. Electrical switching in metallic carbon nanotubes Transformation of Chain Molecules

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

1. Motivation Transformation of Chain Molecules

- 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 Transformation of Chain Molecules

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 Transformation of Chain Molecules

2

: Landauer formalism

SCattering-state appRoach for eLEctron Transport (SCARLET)

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

Nitrogen Boron Transformation of Chain Molecules

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 Transformation of Chain Molecules

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 Transformation of Chain Molecules

∆H ∝ Eext · (diameter)2

6. Switching in (10,10) SWNT with Vacancies Transformation of Chain Molecules

- 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 Transformation of Chain Molecules

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

Summary Transformation of Chain Molecules

- 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 Transformation of Chain Molecules

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

Azobenzene (AB) : C Transformation of Chain Molecules6H5-N=N-C6H5

Transformation between Transformation of Chain MoleculestransAB and cisAB

(Voltage bias using STM)

Geometries of Transformation of Chain MoleculestAB

Geometries of Transformation of Chain MoleculescAB

Optimal geometry of Transformation of Chain MoleculestAB and cAB

STS for Transformation of Chain MoleculestAB and cAB

Disperse Orange 3 (NH Transformation of Chain Molecules2-C6H4-N=N-C6H4-NO2)

Flat geometry of Transformation of Chain MoleculescAB

Summary Transformation of Chain Molecules

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

Appendix Transformation of Chain Molecules

Example of MATERIAL DESIGN : totalreflection by three nitrogen impuritiesImportance 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 E Transformation of Chain Moleculesext 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 | Transformation of Chain Molecules>

where

Reflection for the specific state |> :

Total transmission :

Resonance condition :

Effect of E Transformation of Chain Moleculesext : 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| Transformation of Chain Molecules

(10,10) SWNT with NO E Transformation of Chain Moleculesext 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

SAMSUNG SDI FED Transformation of Chain Molecules– 2005 -

Power consumption of SED, LCD, PDP (36in) Transformation of Chain Molecules

Canon-Toshiba SED at CEATEC2004

SED

LCD

PDP

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