Focusing effect of open tip carbon nanotube

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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
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Collaborators

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

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BasicsSubstitutional Impurity in Metallic Carbon
Nanotubes
Boron or Nitrogen
Tube axis
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Electronic Structure of Metallic Armchair Nanotube
Band structure of a (10,10) single-wall nanotube
( LDA, first-principles pseudopotential method )
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CBM
VBM
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Tube axis
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Conductance with Boron Impurity
Similarity to acceptor states in semiconductors
A
A
H.J. Choi et al, PRL 84, 2917(2000)
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Conductance with Nitrogen Impurity
Similarity to donor states in semiconductors
D
D
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I. Electrical switching in metallic carbon
nanotubes
( Y.-W. Son, J. Ihm, etc., Phys. Rev. Lett. 95,
216602(2005) )
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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)

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1. Motivations contd
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
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2. Calculational Method
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Landauer formalism
SCattering-state appRoach for eLEctron Transport
(SCARLET) H. J. Choi et al, PRB 59, 2267(1999),
and in preparation
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3. B(N) doped (10,10) SWNT
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4. Switching in B-N codoped (10,10) SWNT
B
N

• Switching behavior off/on ratio607kO/6.4kO100
• Maximum resistance depends on the relative
  position between N and B.
• Asymmetric resistance w.r.t. the direction of Eext

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5. Scaling for larger (n,n) SWNT
?H ? Eext ? (diameter)2
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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 ratio1200kO/6.4kO
  200
• Symmetric resistance w.r.t. the direction of Eext

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6. Switching in (10,10) with Vacancies contd
Quasibound states move up or down depending on
the direction of Eext.
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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.

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II. Conformational Transform of Azobenzene
Molecules
( B.-Y. Choi et al., Phys. Rev. Lett. 96,
156106(2006) )
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Azobenzene (AB) C6H5-NN-C6H5
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Transformation between transAB and cisAB
(Voltage bias using STM)
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Geometries of tAB
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Geometries of cAB
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Optimal geometry of tAB and cAB
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STS for tAB and cAB
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Disperse Orange 3 (NH2-C6H4-NN-C6H4-NO2)
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Flat geometry of cAB
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(No Transcript)
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Summary

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

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Example of MATERIAL DESIGN totalreflection by
three nitrogen impurities
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.)
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Difference between Eext and impurity potential U
Lippman-Schwinger formalism Eigenstate ?gt of
Htot associated with the eigenstate ?gt of H0
with the same energy E (with impurity potential U
at site a)
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Projection on to the impurity ?gt
where
Reflection for the specific state ?gt
Total transmission
Resonance condition
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Effect of Eext Greens function itself changes.
G0 projected at site a
With applied electric fields,
Suppose ?H at site a is ?E.
In other words, is G0(aE)
shifted by ?E.
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(10,10) SWNT with single attractive impurity of
U-5t
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Changing Eext is different from changing U.
(10,10) SWNT with a single attractive impurity of
U-5t while changing Eext
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SAMSUNG SDI FED 2005 -
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Power consumption of SED, LCD, PDP (36in)
Canon-Toshiba SED at CEATEC2004
SED
LCD
PDP