1. Carbon Nanotubes Deanna Zhang Chuan-Lan Lin May 12, 2003

2. Overview Introduction History Fabrication Application Summary

3. Introduction I: What is nanotube? Responsible bond: Unit cell: honeycomb pattern Wrapping these patterns back on top of themselves and joining the edges Carbon nanotube

4. Introduction II: Single and Multi-wall nanotube Single wall nanotube: –SWNT –single atomic layer wall, diameter of 1-5 nm –excellent mechanical property – hot topic now Multi wall nanotube: –MWNT –Inner diameter: 1.5 – 15 nm –Outer diameter: 2.5 – 30 nm – ~50 layers –containing more structure defects (http://www.lbl.gov)

5. Introduction III: The Electrical Properties of nanotube Can be either Metal or semiconductor –Controlled by Rolling Direction Ch (rolling vector)= na + mb (unit vector) Rule: = integer metallic non-integer semiconductor Electrical Conductivity –Four Point Probe Method to determine sheet resistance and conductivity

6. Introduction IV: The Other Properties of Nanotube Mechanical: –Young’s Modulus ~ 1TPa (SWNT), 1.25 TPa (MWNT) (Steel: 230 GPa) –Density ~ 1.3 g/cm^3 Thermal: –Conductivity: 2000W/m.K ( copper: 400W/m.K) High Aspect Ratio: Length ~1µm, Diameter ~ 1nm to 50nm

7. History I Buckyball ( ) The discovery of nanotubes comes from Buckyball The discovery of Buckyball is by accident, from Radio- astronomy Around 1970s (http://www.slb.com )

8. History II The History of Nanotubes WhenWhoEvents 1970sHarry Kroto & Dave WaltonTry to synthesize long carbon chains Late 1980sScientists around the worldBuckyball was synthesized and confirmed as C60 1991Japanese Scientist, Sumio IijimaDiscovery of multi wall carbon nanotubes 1993 S, Iijima and T, Ichihashi Synthesis of single wall carbon nanotubes 1996Robert F. Curl, Harry Kroto, Richard E. Smalley Nobel Prize in Chemistry for the discovery of Buckyball 1999SamsungFlat Panel display prototype 2001IBMThe first computer circuit composed of only one single carbon nanotube

9. Fabrication of Carbon Nanotubes Laser Ablation or Pulsed Laser Vaporization Carbon Arc or Arc Discharge Chemical Vapor Deposition (CVD) High pressure (HiPCO)

10. Fabrication I Laser Ablation Target: 1 at.% each of Ni and Co uniformly mixed with graphite 500 m Torr Ar flowing at 50 sccm In the oven at 1473 K Nd:YAG Pulse laser at 60Hz PUREST but yield is very small (~0.4 gram/hour) Developed by NASA JSC Group based on Rice University facility

11. Fabrication II Carbon Arc or Arc Discharge The first available method Electric arc vaporizes an carbon anode containing the catalysts (Ni and Co) He: 500 Torr, Current: 100 amp and 35 volts Chamber is cooled by water Nanotube takes place at the wall inside the chamber Developed by the group at the University of Monpellier, France

12. Fabrication III Chemical Vapor Deposition (CVD) Idea: prepattern the substrate with a catalyst and to grow nanotubes onto these by CVD The key step : deposit the catalyst at predefined locations Advantage: SELECTIVE GROWTH: we can grow nanotube at the place we expect First developed by Xie group in China in 1996 Use hydrocarbons as source

13. Fabrication III: Steps of CVD Deposit photoresist Expose resist Deposit catalyst Etch resist CVD growth of Carbon Nanotube on catalyst

14. Fabrication IV HiPCO Single wall nanotube in gas phase (1200C, 10 atm) CO+CO C+ catalyst: (25 mTorr) Flow high pressure carbon monoxide past catalyst particles at high temperatures Can now produce largely single-walled nanotubes in kilogram quantities Purification steps are unnecessary due to use CO instead of hydrocarbons (P. Nikolaev et al.)

15. Application Transistor –Field Effect transistor –Single electron transistor SPM Tips Field Emission Display Device More Possible Applications

16. Nanotube transistor Field Effect transistor –Similar to MOSFET –Formation of P-type –Annealing or doping with K to form N-type –Use both N and P to make CMOS type circuits

17. SPM Tips Tips of Scanning Probe Microscopes are usually cantilevers or metal wires but seldom survive a tip crash Nanotubes: large aspect-ratio, well- defined end, far more resistant A nanotube was directly grown by CVD on a cantilever ( From J. Hafner et al, Nature 398, 761 (1999))

18. Field Emission Display Device Take advantage of the properties of high current containing and high aspect ratio Useful as the electron source for Flat Panel Display with lower power consuming and high voltage circuit is unneeded Samsung has shown the prototype of 9” full color display with 576 X 242 pixels The first nanotube flat screen TV is expected to be manufactured by the end of 2003 The Samsung 4.5” full-color nanotube display Schematic structure of nanotube flat panel display. ( Choi et al. ) (Cathode) (Anode)

19. More Possible Applications Nanotube sensors (Kong et al.) : –The electrical conductivities of SWNT change dramatically when they expose to gaseous molecules Hydrogen storage (Heben et al.) : –5~10 wt% hydrogen storage density at room temperature for SWNT Light Elements (Saito et al. ) : –Electrons from nanotube bombard a phosphor-coated surface to produce light –2 times brighter, 8000h lifetime, can be used for giant outdoors displays Memory device (Fuhrer et al.) : Capable to store single electronic charge –High mobility

20. Summary and Future work Carbon Nanotubes have unique properties Unique properties lead to fabrication of different devices. Improvements of current fabrication of carbon nanotubes needed to make available commercial products. The totally new world constructed by nanotube is close. Little knowledge about growth mechanism

21. Questions?