Transcript Carbon Nanotubes

Carbon Nanotubes
Deanna Zhang
Chuan-Lan Lin
May 12, 2003
Overview
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Introduction
History
Fabrication
Application
Summary
Introduction I:
What is nanotube?
•Responsible bond: SP 2
•Unit cell: honeycomb pattern
•Wrapping these patterns back on top
of themselves and joining the edges
Carbon nanotube
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:
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MWNT
Inner diameter: 1.5 – 15 nm
Outer diameter: 2.5 – 30 nm
~50 layers
containing more structure
defects
(http://www.lbl.gov)
Introduction III:
The Electrical Properties of nanotube
• Can be either Metal or semiconductor
– Controlled by Rolling Direction
Ch (rolling vector)= na + mb (unit vector)
nm
Rule:
= integer
3
non-integer
metallic
semiconductor
• Electrical Conductivity
– Four Point Probe Method to determine sheet resistance and conductivity
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
History I
Buckyball ( C60 )
• The discovery of
nanotubes comes from
Buckyball
• The discovery of
Buckyball is by
accident, from Radioastronomy
• Around 1970s
(http://www.slb.com )
History II
The 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
Discovery of multi wall carbon
nanotubes
1993
1996
Japanese Scientist, Sumio Iijima
S, Iijima and T, Ichihashi
Robert F. Curl, Harry Kroto ,
Richard E. Smalley
Synthesis of single wall carbon
nanotubes
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
Fabrication of Carbon Nanotubes
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Laser Ablation or Pulsed Laser Vaporization
Carbon Arc or Arc Discharge
Chemical Vapor Deposition (CVD)
High pressure (HiPCO)
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
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
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
Fabrication III:
Steps of CVD
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Deposit photoresist
Expose resist
Deposit catalyst
Etch resist
CVD growth of
Carbon Nanotube on
catalyst
Fabrication IV
HiPCO
• Single wall nanotube in gas phase (1200C, 10 atm)
• CO+CO
C+ CO
catalyst: FeCO5 (25 mTorr)
• Flow high pressure carbon monoxide past catalyst particles at high temperatures
2
• 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.)
Application
• Transistor
– Field Effect transistor
– Single electron transistor
• SPM Tips
• Field Emission Display Device
• More Possible Applications
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
SPM Tips
• Tips of Scanning
Probe Microscopes are
usually cantilevers or
metal wires but
seldom survive a tip
crash
• Nanotubes: large
aspect-ratio, welldefined end, far more
resistant
A nanotube was directly grown by CVD on
a cantilever (From J. Hafner et al, Nature 398, 761 (1999))
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
(Anode)
(Cathode)
Schematic structure of nanotube flat panel display.
(Choi et al.)
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
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
Questions?