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
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
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.
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
Characterization of CNT’s
STM (Scanning tunneling
AFM (Atomic force
SEM (scanning electron
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
Frank et al., Science 280, 1744 (1998).
The Raman effect comprises a very small fraction,
about 1 in 107 of the incident photons.
h 0 h 0 h m
h 0+h m
Raman signals in SWNT’s
Radial breathing mode (observed
up to 3 nm in SWNTs and
D-band (1350 ) –Resonant
G-band (1530 -1620 )
G’ band (depends on diameter of
Other weak features.
Resonance is diameter selective.
Significance of Raman signals
RBM is useful to identify the presence of SWNT’s in
the carbon material and to determine the diameter of
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)
Diameter of the carbon
Breathing mode : 100 – 350
Diameter of nanotube increases with
increase in growth temperature
RBM as a function of diameter
A particular diameter
is excited at a given
In a range of laser
frequency the RBM
plot can be made
which agree well with
Temperature dependence of G-band
Intensity of G-band
decreases exponentially with
The intensity is independent
of surface morphology and
This can be used to measure
the temperature of the
A shift in the G+ peak can
also be observed as the
Distinction of SWNTs, DWNTs and
MWNTs using Raman spectroscopy
and MWNT from
a mixture of sample .
G/D ratio show
MWNTs are low
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.
Characterization of water filled CNT using
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
CNT gas sensors
Chemical doping induces
a strong change in the
concentration gas with
high sensitivity at room
Can detect NO2, NH3 etc.
with fast response time.
(Shu Peng and Kyeongjae Cho,
Department of Mechanical
Engineering, Stanford University)
AFM (atomic force microscopy )
Uses van der Waals force
between the tip and the
Nanotube as AFM tip
Exceptional mechanical strength and large aspect ratio
Survive tip crash due to accidental contact with
Slender and well defined tip, so higher resolution.
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.
•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
• 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)
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
E, modulaus , L -length, t -
thickness, desnsity , effective mass
Most sensitive and smallest balance in the
Poncharal et al., Science (1999) 31
CNT infrared detector
SWNT based IR
detectors have excellent
time, dark current
Electron field emission of CNT
Electric field lines
concentrated on sharp
regions, since CNT have
sharp tip the geometry is
favorable for field
Electron emission can
be observed with about
100 V on single CNT.
Application in field
Novel hard disk
A novel data storage system
capable of 1015 bytes/cm2 is
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
is being investigated.
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.