Jisoon Ihm School of Physics, Seoul National University Electrical Switching in Carbon Nanotubes and Conformational Transformation of Chain Molecules

Collaborators 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 )

VBM CBM

Tube axis

Conductance with Boron Impurity A A Similarity to acceptor states in semiconductors 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, (2005) )

Metallic and semiconducting carbon nanotubes are produced simultaneously. Selection Problem! Semiconducting nanotubes : easy to change conductance using gate Metallic nanotubes: robust against impurities, defects, or external fffffffff fields (difficult to change conductance) C. Dekker, A. Zettl 1. Motivation

Is it possible to control the conductance of metallic single- wall carbon nanotubes? Interplay between defects and electric fields electron flow S.B. Lee, A. Zettl 1. Motivations – cont’d

2. Calculational Method SCattering-state appRoach for eLEctron Transport (SCARLET) H. J. Choi et al, PRB 59, 2267(1999), and in preparation : Landauer formalism 2

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 N B 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 E ext

∆H ∝ E ext · (diameter) 2 5. Scaling for larger (n,n) SWNT

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 E ext

6. Switching in (10,10) with Vacancies – cont’d Quasibound states move up or down depending on the direction of E ext.

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, (2006) )

Azobenzene (AB) : C 6 H 5 -N=N-C 6 H 5

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 (NH 2 -C 6 H 4 -N=N-C 6 H 4 -NO 2 )

Flat geometry of cAB

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

Example of MATERIAL DESIGN : total reflection by three nitrogen impurities Doubly degenerate impurity states cause perfect reflection at 0.6 eV. (Both even and odd states are fully reflected at same energy.) Importance of geometric symmetry (equilateral triangle) Appendix

Difference between E ext and impurity potential U Lippman-Schwinger formalism: Eigenstate | ψ > of H tot associated with the eigenstate |> of H 0 with the same energy E (with impurity potential U at site )

Projection on to the impurity |> where Reflection for the specific state |> : Total transmission : Resonance condition :

With applied electric fields, Suppose ∆H at site α is ∆E. In other words, is G 0 (α;E) shifted by ∆E. : G 0 projected at site  Effect of E ext : Green’s function itself changes.

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

(10,10) SWNT with a single attractive impurity of U=-5|t| while changing E ext EFEF (10,10) SWNT with NO E ext while changing the strength of the attractive potential, U. Changing E ext is different from changing U.

SAMSUNG SDI FED – Picture #1 Picture #2 Picture #3 Picture #4

Power consumption of SED, LCD, PDP (36in) SED LCD PDP Canon-Toshiba SED at CEATEC2004