Carbon nanotubes have unique electrical, mechanical, and thermal properties that make them promising for a variety of applications. They have very high tensile strength and thermal conductivity. Their properties depend on their geometry, with single-walled nanotubes being metallic or semiconducting depending on their structure. Common synthesis methods include arc discharge, laser ablation, and chemical vapor deposition. Raman spectroscopy is useful for characterizing carbon nanotubes and can determine their diameter and identify defects. Potential applications of carbon nanotubes include use in electronics, gas sensors, field emission displays, and energy storage.

1. PRESENTED BY:
JUSTIN GEORGE
University of Antwerpen
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2. Allotropic forms of carbon
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3. why carbon naotubes are so special?
 Electrical properties depend on geometry of nanotube
 Tremendous current carrying capacity
1 billion Amps/cm2
 Excellent heat conductor
twice as good as diamond
 High strength
much higher than high-strength steel
 Young Modulus ~ 1 TPa (SWNT) and 1.25 TPa (MWNT) (Steel: 230 Gpa)
 High Aspect Ratio: 1000 – 10,000
 Density: 1.3 – 1.4 g/cm3
 Maximum Tensile Strength: 30 GPa
 Thermal Conductivity: 2000 W/m.K (Copper has 400 W/m.K)
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4. What is carbon nanotubes?
 Carbon nanotubes are a hexagonal shaped
arrangement of carbon atoms that has been rolled into
tubes.
Composites Science and Technology 61
(2001) 1899–1912
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5. Carbon naotube family
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6. Classification of carbon nanotubes
 Single walled carbon nanotubes (SWNT) (0.4 -2 nm)
 Multiwalled carbon nanotubes (MWNT) (2-100 nm)
 Metallic (n =m or n-m =3i, i is an interger)
 Semiconductor (all other cases)
Depends on the geometry
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7. Diameter of the tube and chiral vector.
 The diameter d of the carbon nanubes are given by
Where is the nearest carbon-carbon bond
length and C is the chiral vector or roll-up vector.
where the chiral angle
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8. Carbon nanotube synthesis
 Arc discharge
 Laser ablation
 CVD (chemical vapour deposition)
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9. Arc discharge method
 cathode gets
consumed, CNTs in
cathodic soot
 structure of CNTs
depends on: current
I, voltage V, He gas
pressure, anode
material, distance
between the
electrodes
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10. Arc discharge method
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11. Laser vaporization
 Laser vaporizes the graphite target at high
temperature in an inert atmosphere
 nanotubes formed at the cooler surface of the
chamber as the vaporized carbon condenses.
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12. Catalytic method
 Hydrocarbon in contact with hot metal nano particles
and decompose into hydrogen and carbon
 If the interaction with catalytic substrate is weak the
carbon diffuses down and push the nano particle up
“tip-growth model”
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13. Characterization of CNT’s
 STM (Scanning tunneling
microscopy )
 AFM (Atomic force
microscopy)
 TEM (transmission
electron microscopy)
 SEM (scanning electron
microscopy)
 Raman spectroscopy
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14. Quantum Effect
 Conductance appears to be ballistic over micron scales,
even at room temperature.
 Ballistic = no dissipation in the tube itself = very high
current densities are possible.
 Conductance increase with more CNTs are in contact with
liquid metal.
 Frank et al., Science 280, 1744 (1998).
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15. Energy
Rayleigh
Scattering
(elastic)
The Raman effect comprises a very small fraction,
about 1 in 107 of the incident photons.
Stokes
Scattering
Anti-Stokes
Scattering
h 0
h 0
h 0
h 0 h 0 h m
h 0+h m
E0
E0+h m
Raman
(inelastic)
Virtual State

16. Raman scattering of CNT
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17. Raman signals in SWNT’s
 Radial breathing mode (observed
up to 3 nm in SWNTs and
MWNTs )
 D-band (1350 ) –Resonant
nature.
 G-band (1530 -1620 )
 G’ band (depends on diameter of
CNTs)
 Other weak features.
 Resonance is diameter selective.
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18. Significance of Raman signals
 RBM is useful to identify the presence of SWNT’s in
the carbon material and to determine the diameter of
SWNT’s.
 G-mode corresponds to planar vibrations of carbon
naotubes and is present in graphite like material
( carbon materials )
 D-mode generate from the structural defects of
graphite like carbon.
 G/D ratio is used to find quality of carbon nanotubes
(higher ratio, higher quality)
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19. Radial-Breathing Mode
Diameter of the carbon
nanotube
Breathing mode : 100 – 350
The growth
temperature,
Diameter of nanotube increases with
increase in growth temperature
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20. RBM as a function of diameter
 A particular diameter
is excited at a given
laser frequency
(Resonance Raman
effect)
 In a range of laser
frequency the RBM
frequency –diameter
plot can be made
which agree well with
the theory.
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21. Temperature dependence of G-band
 Intensity of G-band
decreases exponentially with
temperature.
 The intensity is independent
of surface morphology and
preparation method.
 This can be used to measure
the temperature of the
sample.
 A shift in the G+ peak can
also be observed as the
temperature increases.
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22. Distinction of SWNTs, DWNTs and
MWNTs using Raman spectroscopy
 Can distinguish
SWNT, DWNT
and MWNT from
a mixture of sample .
 G/D ratio show
MWNTs are low
quality.
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23. Identify metallic and semiconductor
SWNT using Raman spectra.
 Frequency is independent of diameter but
depends on diameter and metallic and semiconductor
nature of SWNT .
 The frequency downshift of metallic SWNT is more
than semiconductor SWNT.
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24. Characterization of water filled CNT using
Raman spectroscopy
 Resonance Raman
spectra of SWNT (a) S1
raw sample (c) air
oxidized and acid
treated sample (used to
open the SWNT).
 (b) and (d) are S1 and S2
respectively with empty
(0) and filled
nanotubes.

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25. Nanotube elecronics
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26. CNT gas sensors
 Chemical doping induces
a strong change in the
conductance.
 Detect small
concentration gas with
high sensitivity at room
temperature.
 Can detect NO2, NH3 etc.
with fast response time.
(Shu Peng and Kyeongjae Cho,
Department of Mechanical
Engineering, Stanford University)
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27. AFM (atomic force microscopy )
 1. Laser
 2. Mirror
 3. Photodetector
 4. Amplifier
 5. Register
 6. Sample
 7. Probe
 8. Cantilever
 Uses van der Waals force
between the tip and the
surface
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28. Nanotube as AFM tip
 Exceptional mechanical strength and large aspect ratio
 Survive tip crash due to accidental contact with
observation surface
 Slender and well defined tip, so higher resolution.
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29. CNT mechanical sensors
 Conductance decreases as
the AFM tip pushes the
nanotube down, but recovers
as the tip retracts.
 Full reversibility of
conductance, so can be used
as a mechanical sensor.
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30. CNT Nanothermometer
•Continuous, uni-dimensional column of Gallium in CNT
•Gallium has greatest liquid range (30 – 2,403 °C) and low vapour
pressure at high temperature.
• Height of liquid gallium varies linearly and reversibly with
temperature
• Expansion coefficient same as macroscopic gallium.
• Gallium meniscus perpendicular to inner surface of CNT
• Easy to read and suitable for microenvironment.
Gao and Bando, Nature (2002)
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31. CNT nanobalance
 Nanobalance can measure a mass
small as 22 fg (femtogram)
 Time dependent voltage applied
cause time dependent force and
dynamic deflection, by adjusting the
frequency resonance excitation can
be achieved
 E, modulaus , L -length, t -
thickness, desnsity , effective mass
Most sensitive and smallest balance in the
world
Poncharal et al., Science (1999) 31

32. CNT infrared detector
 SWNT based IR
detectors have excellent
sensitivity, response
time, dark current
characteristics.
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33. Applications of carbon nanotubes
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34. Blacker than black
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35. Electron field emission of CNT
 Electric field lines
concentrated on sharp
regions, since CNT have
sharp tip the geometry is
favorable for field
emission.
 Electron emission can
be observed with about
100 V on single CNT.
 Application in field
emission display.
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36. Novel hard disk
 A novel data storage system
capable of 1015 bytes/cm2 is
being explored.
In this system, H atoms
would be designated as 0
and F atoms as 1.
A tip that can distinguish
between 0 and 1 rapidly and
unambiguously
is being investigated.
 http://www.ipt.arc.nasa.go
v/datastorage.html
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37. Other applications
 Gas storage – as CNT has very large surface area gases
like Hydrogen can be absorbed and stored
 Super capacitor- can store large amount of energy and
can deliver very high peak power (CNT supercapacitor
have 7 times more energy density than commercial
activated carbon based supercapacitor)
 Nanomachines- CNT based nanogear with benzene
molecule bonded as teeth.
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38. Thank you
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