Loading in 2 Seconds...

Jisoon Ihm School of Physics, Seoul National University

Loading in 2 Seconds...

- 139 Views
- Uploaded on

Download Presentation
## PowerPoint Slideshow about ' Jisoon Ihm School of Physics, Seoul National University' - harsha

**An Image/Link below is provided (as is) to download presentation**

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

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.)
- Young-Woo Son ,Marvin Cohen, Steven Louie (Berkeley)

Electronic Structure of Metallic Armchair Nanotube

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

VBM

Conductance with Boron Impurity

Similarity to acceptor states in semiconductors

A

A

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

I. Electrical switching in metallic carbon nanotubes

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

- 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)

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

: Landauer formalism

SCattering-state appRoach for eLEctron Transport (SCARLET)

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

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.

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.

II. Conformational Transform of Azobenzene Molecules

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

Transformation between transAB and cisAB

(Voltage bias using STM)

Summary

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

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.)

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 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

Download Presentation

Connecting to Server..