CARBON-NANOTUBES
TECHNICAL SEMINAR
PRESENTED BY : SHUHAB-U-TARIQ
USN : 1SI03EC109
OUTLINE
 CARBON NANOTUBES
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Definition
Structure
Classification
Properties
Applications
Drawbacks
Conclusion
Definition
 Carbon Nanotubes
 allotropes of carbon.
 extremely thin hollow
cylinders made of
carbon atoms.
 cylinderical fullerenes.
Structure
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The name is derived from their size.
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The diameter of a nanotube is
about 10000 to 50000 times smaller
than the width of a human hair.
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Nanotubes are composed entirely of
sp² bonds, similar to those of graphite.
This bonding structure (stronger than sp³
bonds found in diamond) is responsible
for their unique strength.
Classification of Carbon Nanotubes
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Based on Conductivity
metallic
semiconducting
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Based on Chirality
zig-zag
armchair
chiral
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Based on Layers
single-walled
multi-walled
Classification based on Conductivity
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The conductance of a CNT is
mainly affected by its chirality.
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Twisting is found to transform
a metallic nanotube to a semiconducting one with a band-gap
that varies with the twist angle.
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Metallic nanotubes can carry
extremely large current densities.
Semiconducting nanotubes can be
electrically switched ON & OFF as
FETs.The two types can also be
joined covalently.
Classification based on Chirality
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Described by chiral
vector (n,m) where
n & m are integers of
vector =n,
R = na1 + ma2
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If R-vector lies along
the armchair line, i.e.
If Φ=0° … Armchair
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If Φ=30°
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If 0°<Φ<30° … Chiral
… Zig-Zag
Chirality Classification Contd.
Chirality Classification Contd.
 n=m
-- m=0
-- otherwise ---
armchair
zig-zag
chiral
Conductivity & Chirality
 If (n-m)/3 = 0 , tube is metallic
 If (n-m)/3 ≠ 0 , tube is semi-conducting
 Armchair (n=m) tubes are metallic
 Zig-Zag (m=0) & Chiral tubes are semi-conducting
Classification based on Layers
 Single-walled CNTs
 SWNTs have one shell of
C-atoms in a hexagonal
arrangement.
 They can be thought of as
a sheet of graphite rolled
into a cylinder of about 1.2
to 1.4 nms in diameter.
Layers Classification Contd.
 Multi-walled CNTs
 MWNTs consist of multiple
concentrically nested C-tubes.
 Russian Doll model MWNTs
 Parchment model MWNTs
PROPERTIES
 Size :
0.6 to 1.8 nm in diameter.
 Density :
1.33 to 1.40 grams/cm³.
To make a comparison, Aluminium has a density of 2.7 grams/cm³.
 Tensile strength :
45 billion Pa. In comparison, high strength steel alloys break at
about 2 billion pascals. High Elastic Modulus of about 1 TPa.
 Resilience :
Can be bent at large angles easily (high ductility) and re-straightened
without damage.
PROPERTIES CONTD.
 Current carrying capacity :
Estimated at a 1 billion amps/cm². i.e. more than 1000 times
greater than metals such as silver & copper--(Cu-wires burn at about 1 million amps/cm²).
 Heat transmission :
Predicted to be as high as 6,000 watts per meter per kelvin at
room temperature. Compare this to copper (a metal well known for
its thermal conductivity) which only transmits 385 W/m/K.
 Temperature stability :
Stable up to 2,800 °C in vacuum, 750 °C in air.
PROPERTIES CONTD.
 Defects
 In the form of atomic vacancies.
 Stone Wales Defect – creation of pentagonal and
heptagonal pair by rearrangement of bonds.
 Tensile strength dependent on the weakest segment.
 Lowered conductivity through defective region of tube.
Applications of Carbon-nanotubes
 The physical properties of C-nanotubes make them of
potential use in nanotechnology engineering.
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Energy Storage (for fuel cells)
Composite Materials
Field Emitting Devices (flat panel displays)
X-rays to go : CNTs could shrink machines
Nanotube Chemical Sensors
CNTs used for Cheaper Desalination
Applications Contd.
 Transistors
 Basic building blocks of ICs.
 CNT – acts as a channel between source &
drain in a CNT-FET.
 Gain of CNT-transistor is 10-100 times more
than Si-transistors used for present day ICs.
Applications Contd.
 Disadvantage of these conventional CNT-FETs.
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Electric current significantly fluctuates with time.
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Current-voltage characteristic exhibits a hysterisis.
Diagram of a conventional CNT-FET ( IBM Nanoscience Department )
 Successful development of a CNT-FET with an operational
stability more than 1000 times than that of conventional
CNT-FETs.
 Surface of CNT covered with Silicon-nitride film
Applications Contd.
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Stability of new CNT-FET almost 1000 times more.
Applications Contd.
 Removal of time & voltage instability leading to a
successful development of CNT-FETs.
Drawbacks of Carbon-nanotubes
 Cost – approx.$1,500 per gram.
High-quality nanotubes produced in very
limited quantities – commercial nanotube soot
costs 10 times as much as gold.
 Polydispersity in nanotube type. Can’t be
produced selectively.
 Lack of synthesis & purification methods.
 Separation of CNTs after synthesis.
 No control over CNT length & chirality.
Conclusion
“The Next Big Thing Is Really Small”
 The remarkable properties of CNTs appear destined to
open up a host of new practical applications & help
improve our understanding of basic physics at
nanometer-scale.
 CNTs – envisioned to be the most viable candidates to
dominate the 21st century revolution in nanotechnology.
References
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Physics of Carbon-nanotubes (by M. S.Dresselhaus and R.Saito, M.I.T)
Nanotubes for Electronics (by Philip G.Collins and Phaedon Avouris)
Carbon Nanotube Applications in Microelectronics (by G.S.Dusberg)
Carbon Nanotubes for Electronic Applications (by W.I.Milne, Cambridge University)
Carbon Nanotubes (by Anthony Kendall and Elizabeth Pfaff)
Phisical Properties of Carbon Nanotubes (by Thomas A. Adams)
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http://www.nanotech-now.com
http://www.azonano.com
www.research.ibm.com/nanoscience/nanotubes.html
http://en.wikipedia.org/wiki/Carbon_nanotube
www.knowledgefoundation.com/nanotubes2000.html
www.nature.com/nature/journal/v439/n7074/abs/439281a.html
www.amazon.com/Carbon-Nanotubes-Synthesis-Properties-Applications/dp/3540410864
www.chm.bris.ac.uk/webprojects2001/andrews/nanotubes-uses.html