Carbon Nanotubes
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Transcript of Carbon Nanotubes
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Carbon Nanotubes
Deanna Zhang
Chuan-Lan Lin
May 12, 2003
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Overview
• Introduction
• History
• Fabrication
• Application
• Summary
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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
2SP
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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)
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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
3
mn
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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
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History IBuckyball ( )
• The discovery of nanotubes comes from Buckyball
• The discovery of Buckyball is by accident, from Radio-astronomy
• Around 1970s
60C
(http://www.slb.com )
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History IIThe History of Nanotubes
When Who Events
1970s Harry Kroto & Dave Walton Try to synthesize long carbon chains
Late 1980s Scientists around the world Buckyball was synthesized and confirmed as C60
1991 Japanese Scientist, Sumio Iijima Discovery of multi wall carbon nanotubes
1993S, Iijima and T, Ichihashi Synthesis of single wall carbon
nanotubes
1996 Robert F. Curl, Harry Kroto ,
Richard E. Smalley Nobel Prize in Chemistry for the discovery of Buckyball
1999 Samsung Flat Panel display prototype
2001 IBM The first computer circuit composed of only one single carbon nanotube
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Fabrication of Carbon Nanotubes
• Laser Ablation or Pulsed Laser Vaporization
• Carbon Arc or Arc Discharge
• Chemical Vapor Deposition (CVD)
• High pressure (HiPCO)
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Fabrication ILaser 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
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Fabrication IICarbon 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
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Fabrication IIIChemical 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
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Fabrication III:Steps of CVD
• Deposit photoresist
• Expose resist
• Deposit catalyst
• Etch resist
• CVD growth of Carbon Nanotube on catalyst
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Fabrication IVHiPCO
2CO
• 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.)
5FeCO
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Application
• Transistor– Field Effect transistor– Single electron transistor
• SPM Tips
• Field Emission Display Device
• More Possible Applications
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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 typecircuits
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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))
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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)
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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
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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
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Questions?Questions?