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Master Presentation Part 1

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Master Presentation Part 1

  1. 1. Localized Growth of Multi-Walled Carbon Nanotubes (MWCNT) Chung Yeung Cho Dec 4, 2006 Master Project Presentation Advisors: Prof Liwei Lin, Prof Tsu-Jae King Just Grow It!
  2. 2. Agenda <ul><li>CNT background </li></ul><ul><li>Localized growth of CNT </li></ul><ul><li>Electrical properties discussions </li></ul><ul><li>Pressure-sensing capability </li></ul><ul><li>CNT-based electrode probe </li></ul><ul><li>Conclusion </li></ul>
  3. 3. What can CNT do? <ul><li>a) [1], b) [2], c) [3], d) [4], e) [5], f) [6], g) [7] (References in last slide) </li></ul>
  4. 4. What is a CNT? <ul><li>References: [8] </li></ul>
  5. 5. Why the interest in CNT? <ul><li>Metallic (10 9 A/cm 2 vs 10 5 A/cm 2 for metals) </li></ul><ul><li>Semiconducting (bandgap depands on diameter and chirality) </li></ul><ul><li>High modulus and strength (density-modulated ~19, ~56 times of steel) </li></ul><ul><li>Thermal conductivity (measured 3000 W/m-K vs 2300 W/m-k for diamond) </li></ul>
  6. 6. Fabrication methods <ul><li>a) Arc Synthesis, b) Laser Ablation, c) CVD [9] </li></ul>
  7. 7. Fabrication methods <ul><li>a) Arc Synthesis [10], b) Laser Ablation [11], c&d) CVD [12, 13] </li></ul>
  8. 8. Alignment <ul><li>a) Gas-flow [14], b) PECVD [15], c) Electric field [16] </li></ul>b)
  9. 9. Fabrication Challenges <ul><li>Entanglement of CNT requires post-treatment </li></ul><ul><li>Positioning/manufacturing of CNT devices in a parallel manner </li></ul><ul><li>Elevated fabrication temperature </li></ul><ul><li>Repeatable, controlled growth </li></ul>
  10. 10. Localized growth of CNT <ul><li>On-chip MEMS heater </li></ul>
  11. 11. Setup
  12. 12. Fabrication conditions <ul><li>Pressure: ~250 Torr </li></ul><ul><li>Temperature: >850 o c </li></ul><ul><li>Flow rate: Ar/C 2 H 2 (50/50 sccm) </li></ul><ul><li>Electric field: 0.6-1 V/µm </li></ul><ul><li>Gap: 5-10 µm </li></ul><ul><li>Catalyst: Ni/Fe (80%/20%) </li></ul>
  13. 13. Electric field manipulation <ul><li>Vary the field (~0.6-1V/um) </li></ul><ul><li>Vary heater’s shape </li></ul>
  14. 14. Observations <ul><li>Diameter ~50nm </li></ul><ul><li>Length: 5-10µm </li></ul><ul><li>Growth rate: ~3µm/min </li></ul><ul><li>More CNTs on positive end </li></ul>
  15. 15. Observations <ul><li>~Periodic 34 0 kink angle </li></ul><ul><li>“ Burnt-out”CNTs </li></ul>
  16. 16. Effects of fabrication conditions <ul><li>Growth Rate </li></ul><ul><ul><li>~3 µm/min to ~0.5 µm/s (50 to 100 SCCM, C 2 H 2 ) </li></ul></ul><ul><ul><li>~3 µm/min to ~0.6 µm/s (additional 0.5 - 1V) </li></ul></ul><ul><li>CNT morphology </li></ul><ul><ul><li>Straight </li></ul></ul><ul><ul><li>Diameter: < 10nm </li></ul></ul>
  17. 17. Growth mechanism <ul><li>Precipitation after carbon saturation on catalyst surface </li></ul><ul><li>Nanotubes formed due to nano-scale </li></ul>a) Growth Mechanism [9], b) Base Growth [17], c) Tip Growth[18]
  18. 18. Growth mechanism
  19. 19. In-situ controlled growth

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