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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Electrical Switching in Carbon Nanotubes and Conformational Transformation of Chain Molecules
2006. 8. 30
School of Physics, Seoul National University
Basics:Substitutional Impurity in Metallic Carbon Nanotubes
Boron or Nitrogen
Electronic Structure of Metallic Armchair Nanotube
Band structure of a (10,10) single-wall nanotube ( LDA, first-principles pseudopotential method )
Conductance with Boron Impurity
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
I. Electrical switching in metallic carbon nanotubes
( Y.-W. Son, J. Ihm, etc., Phys. Rev. Lett. 95, 216602(2005) )
C. Dekker, A. Zettl
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
2. Calculational Method
: 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
5. Scaling for larger (n,n) SWNT
∆H ∝ Eext · (diameter)2
6. Switching in (10,10) SWNT with Vacancies
6. Switching in (10,10) with Vacancies – cont’d
Quasibound states move up or down depending on the direction of Eext.
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
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
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 |>
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.
(10,10) SWNT with a single attractive impurity of U=-5|t| while changing Eext
SAMSUNG SDI FED – 2005 -
Canon-Toshiba SED at CEATEC2004