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Image-potential States in Carbon Nanotubes

Image-potential States in Carbon Nanotubes. 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

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Image-potential States in Carbon Nanotubes

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  1. Image-potential States in Carbon Nanotubes

  2. 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 Synthesis of a Carbon nanotube 1991 S. Iijima, Nature (London) 354, 56 (1991) 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, 162-163 (1985).

  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, 135506 ( September 2002)

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

  12. VTotal VJellium inner nanotube outer nanotube Model potential

  13. SWNT MWNT

  14. Nanotube diameter effects • Diameter distribution • SWNT 0.8-1.4 nm • MWNT 5-100 nm

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

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

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

  18. Nanotube samples 10 mm 0.2 mm 10 mm Bucky paper

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