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The Family of Carbon |
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Diamond sp3 Bonding, hard and
insulating |
Graphite: sp2 Bonding
Soft between graphene layers |
C60 “bucky-ball”:
sp2+sp3
~1x10-9 m (1nm) in diameter
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Carbon Nanotube:
sp2+sp3, 0.4-50nm in diameter, 0.1 -
1000 micrometer long
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Types
of Carbon Nanotubes |
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Multi-walled
Carbon Nanotubes, first directly
observed by TEM, S. Iijima |
 
Bundle of Single Wall
Carbon Nanotubes |
|
 
SWNTs can be either metallic or
semiconducting depending on different chirality (See
a movie)
Metallic: 1. (n,n) armchair 2. n-m=3i;
Semiconducting: 1. (n,0) Zigzag 2. all of others
1/3 of carbon nanotubes are metallic if chirality
distribution is random. |
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Mechanical
Properties |
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The strength of the composite is enhanced
L. Jin etc. APL 1998 |
The same high modulus as diamond but tougher
and 1000X stronger than steel |
 |
|
Young's modulus, tensile strength and density
of carbon nanotubes compared with some other materials
|
Material |
Young's modulus (GPa) |
Tensile Strength (GPa) |
Density (g/cm3) |
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Single wall nanotube |
1054 |
150 |
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|
Multi wall nanotube |
1200 |
150 |
2.6 |
|
Steel |
208 |
0.4 |
7.8 |
|
Epoxy |
3.5 |
0.005 |
1.25 |
|
Wood |
16 |
0.008 |
0.6 | |
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Electronic
Properties |
Cees Dekker, Physics Today, May1999 P22 |
 |
| |
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Thermal
Properties |
Thermal conductivity vs. T for (10,10)
Tube
(S. Berber, et al 84, 4613(2000)) |
Comparison of (10,10) tube with graphite and
graphite monolayer |
 |
Carbon Nanotubes are stable
at high temperature
- Carbon nanotubes are stable in Ar environment.
- Carbon nanotubes are very strong against strong acid and
high temperature because of their perfect conjugated system.
Acid and heat are often applied to purify carbon nanotubes.
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Electrochemical
Properties |
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New negative electrode for rechargeable Li
batteries
Anode: Li Cathode: CNT/graphite film
Discharge: Intercalation of Li into
CNT/graphite film
Charge: De-intercalation out of CNT/graphite
film
B. Gao et al. Chem Phys Lett. 1999 |
 |
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Field
Emission Properties of Carbon
Nanotubes |
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What is
Field Emission?
Filed
emission is emission of electrons from the surface of a
condensed phase into another phase usually vacuum, under the
action of a high electrostatic field (108 V/cm). It
is a quantum effect.
 |
Flower-Nordheim Equation
At a metal
surface, electrons near the Fermi Level can overcome the
energy barrier to escape to the vacuum level.
Basic
Form of F-N Equation
i is the
current density in A/cm^2, E is the applied Field in V/cm, Ø
is the work function.
Linear graph of Ln(I/V^2) vs. 1/V with the slope
K=-bØ^(3/2)<0 |
|
Field
Emission From Carbon Nanotubes
CNTs have
excellent materials properties which make them have attractive
field emission characteristics.
-
Large
aspect ratio(>1000)
-
Atomically
Sharp tips
-
High
temperature and chemical stability
-
High
electrical and thermal conductivity
 |
Typical I-V
Characteristics of Carbon Nanotubes
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