1. Image-potential States in Carbon Nanotubes
Nathan Woody
Arifa Habib
Himadri Chakraborty
Uwe Thumm
Patrick Richard

2. Calculation of image potential states
PLAN
Introduction
Carbon nanotube
Image states
Time-resolved two photon photoemission
Calculation of image potential states
Model potential
Binding energies for SWNT and MWNT
Nanotube bundles
Experimental setup
Pump-probe optics
Electron Spectrometer
Nanotube samples

3. Historical Overview 1985 Discovery of fullerenes
"C-60 - Buckminsterfullerene."
H. W. Kroto, J. R. Heath, S. C. Obrien, R. F. Curl and R. E. Smalley.
Nature, 318, (1985).
Synthesis of a Carbon nanotube
1991
S. Iijima, Nature (London) 354, 56 (1991)

4. Nanotube geometries

5. Nanotube geometries
Single walled nanotube
Multi walled nanotube

6. Potential Applications of Carbon nanotubes
Field Emission
Energy Storage
Molecular Electronics
Biomedical Applications
Thermal Materials
Structural Composites
Fibers and Fabrics

7. Image-potential states
Negative charge
Positive charge
-0.5 eV

8. Tubular Image States In
Carbon nanotubes
B. E. Granger et al., Phys. Rev. Lett. 89, ( September 2002)

9. Time-Resolved TPPE Vacuum level Fermi level Occupied bands
Our simulation for a SWNT
1.5 eV
Projected
probe effect
Vacuum level
n=1
4.52eV
Projected
pump effect
Fermi level
DOS
For (9,9) SWNT
Occupied bands

10. Time-Resolved TPPE Binding energy of the state
Phase of the wave function
2-D projection of an electron momentum

11. Low-angular momentum image potential states
Tubular image states
Image-potential states
with l<6
Lower binding energies
Localize closer to a nanotube
More accessible experimentally
Dependence of image-potential states on the nanotube diameter
Centrifugal barrier
Binding energies
Image-potential states in Multi walled nanotubes
Isolated nanotubes
Easier to produce

12. Model potential
VTotal
VJellium
inner
nanotube
outer

13. SWNT
MWNT

14. Nanotube diameter effects
Diameter distribution
SWNT nm
MWNT nm

15. Formation of the image potential well between nanotubes
Nanotube bundles
Effective potential (eV)
0.6
2.3
3.0
-3.0
X, (nm)
Y, (nm)
Veff (eV)
Formation of the image potential well between nanotubes
Tendency of SWNTs to form bundles (ropes)

16. Experimental setup: Laser system
Delay stage
3hω
Harmonics separator
Beam Splitter
λ/2
f = 15 cm
f = 17.5 cm
CCD

17. Electron Spectrometer
Double magnetic shielding
0 V
300 V
Backgammon detector

18. Nanotube samples
0.2 mm
10 mm
Bucky paper