Nanotechnology
Lecture 3 Carbon Nanotubes
Carbon nanotubes
•Introduction of Carbon Nanotubes
•History and Impacts
•Structure of Carbon Nanotubes (SWNT MWNT)
•Properties of Carbon Nanotubes
•Synthesis of Carbon Nanotubes (fabrication)
•Potential and current Applications
What is Carbon Nanotube?
Introduction of Carbon Nanotube
• Allotropes of carbon (graphite ， diamond ， Amorphous
carbon and Fullerene ) (cylindrical members of the fullerene
structural family)
• with a nanostructure. length-to-diameter ratio of up to
132,000,000:1,which is significantly larger than any other
material.
• extraordinary strength and unique electrical properties, efficient
thermal conductors. (limited by their potential toxicity)
• amazing objects? creates by accident, without meaning to, but
that will likely revolutionize the technological landscape of the
century ahead.
• Our society stands to be significantly influenced by carbon
nanotubes, shaped by nanotube applications in every aspect, just
as silicon-based technology still shapes society today.
History and Impacts
• Carbon nanotubes have been synthesized for a long time as products
from the action of a catalyst over the gaseous species originating from
the thermal decomposition of Hydrocarbons.
• The worldwide enthusiasm came unexpectedly in 1991, after the
catalyst-free formation of nearly perfect concentric multiwall carbon
nanotubes (c-MWNTs） was reported as by-products of the formation
of fullerenes by the electric-arc technique.
• Consequently, about five papers a day with carbon nanotubes as the
main topic are currently published by research teams from around the
world, an illustration of how extraordinarily active – and highly
competitive – is this field of research.
• Economical aspects are leading the game to a greater and greater
extent. According to experts, the world market is predicted to be more
than 430M$ in 2004 and estimated to grow to several b $ before 2009.
Structure of Carbon Nanotubes
• Carbon nanotubes are fullerene-related structures which
consist of graphene cylinders closed at either end with caps
containing pentagonal rings(五角环).
Discovered in 1991 by the
Japanese electron microscopist
Sumio Iijima.
Nanotubes could be produced in bulk
quantities by varying the arcevaporation conditions.
Tetrahedral Junction of four
Nanotubes
Nanotube w/
hemispheric
Structure of Carbon Nanotubes
Single-Wall Nanotubes SWNTs
The (n,m) nanotube naming
scheme can be thought of as a
vector (Ch) in an infinite graphene
sheet that describes how to "roll
up" the graphene sheet to make
the nanotube. T denotes the tube
axis, and a1 and a2 are the unit
vectors of graphene in real space.
Most single-walled nanotubes (SWNT) have a diameter of close to 1 nanometer, with a tube length that can be many
millions of times longer. The structure of a SWNT can be conceptualized by wrapping a one-atom-thick layer of
graphite called graphene into a seamless cylinder. The way the graphene sheet is wrapped is represented by a pair of
indices (n,m) called the chiral vector. The integers n and m denote the number of unit vectors along two directions in
the honeycomb crystal lattice of graphene. If m = 0, the nanotubes are called "zigzag". If n = m, the nanotubes are
called "armchair". Otherwise, they are called "chiral".
Single-Wall Nanotubes SWNTs
Armchair (n,n)
Zigzag (n,0)
The chiral vector is
bent, while the
translation vector
stays straight
Chiral (n,m)
Graphene
nanoribbon
n and m can be
counted at the end
of the tube
The chiral vector is
bent, while the
translation vector
stays straight
Graphene
nanoribbon
Single-Wall Nanotubes SWNTs
(n,0)
zigzag nanotube (9, 0)
(n,n)
armchair nanotube (5, 5)
(n,m)
helical (chiral)
nanotube (10,5)
- hexagonal rings,
pentagonal rings at each tips;
- C=C bond and C≡C bond,
( n and m are the integers of the vector OA consideringinducing a unique versatile
electronic behavior.
the unit vectors a1 and a2. )
Single-Wall Nanotubes SWNTs
Fig. 3.3 Image of two neighboring chiral SWNTs within a
SWNT bundle as seen by high resolution scanning
tunneling microscopy (by courtesy of Prof. Yazdani,
University of Illinois at Urbana, USA)
SWNT Rope
Multiwall Nanotubes MWNT
•Multi-walled nanotubes (MWNT) consist
of multiple rolled layers (concentric
tubes) of graphite;
•In the Russian Doll , sheets of graphite
are arranged in concentric cylinders;
•In the Parchment model, a single sheet
of graphite is rolled in around itself,
resembling a scroll of parchment or a
rolled newspaper. (3.3 Å);
Fig. 3.5 (longitudinal view) of a concentric multiwall carbon nanotube (c-MWNT)
prepared by electric arc. In insert, sketch of the Russian-doll-like display of
graphenes
Multiwall Nanotubes MWNT
(a) as-grown.
The
nanotube surface
is made of free
graphene edges.
(b) after 2,900 ◦C heat-
treatment. Both the
herringbone and the
bamboo textures
have become obvious.
Fig. 3.6a,b A herringbone(箭尾型）
(and bamboo) multi-wall
nanotube (bh-MWNT, longitudinal view) prepared by CO
disproportionation on Fe-Co catalyst.
Fig. 3.7 (a) A bamboo-herringbone multi-wall nanotube (bh-MWNT)
showing the nearly periodic feature of the texture,which is very
frequent; (b) high resolution image of a bamboo-concentric multiwall nanotube (bc-MWNT) .
They are sometimes referred as “nanofibers”.
Nanobud
•carbon nanotubes + fullerenes.
•useful properties of both fullerenes and
carbon nanotubes.
•In particular, they have been found to be
exceptionally good field emitters.
• In composite materials, the attached
fullerene molecules may function as
molecular anchors preventing slipping of
the nanotubes, thus improving the
composite’s mechanical properties
Extreme carbon nanotubes
•The longest carbon nanotubes (18.5 cm long) was reported in 2009. These
nanotubes were grown on Si substrates using an improved chemical vapor
deposition (CVD) method and represent electrically uniform arrays of singlewalled carbon nanotubes
•The thinnest carbon nanotube is armchair (2,2) CNT with a diameter of 3 Å
•The thinnest free standing single-walled carbon nanotube is about 4.3 Å
in diameter. Researchers suggested that it can be either (5,1) or (4,2)
SWCNT, but exact type of carbon nanotube remains questionable.
Properties of Carbon Nanotube
Strength
•the strongest and stiffest materials .
•In 2000, a MWCN was tested to have a tensile strength of 63 gigapascals (the
ability to endure tension of 6300 kg on a cable with cross-section of 1 mm2.)
•low density for a solid of 1.3 to 1.4 g·cm−3
•Standard single walled carbon nanotubes can withstand a pressure up to
24GPa without deformation (hardness)
Kinetic
Multi-walled nanotubes, multiple concentric nanotubes precisely nested within
one another, exhibit a striking telescoping property whereby an inner nanotube
core may slide, almost without friction, within its outer nanotube shell thus
creating an atomically perfect linear or rotational bearing.
Electrical
moderate semiconductor.
Synthesis of Carbon Nanotube
1 Laser Ablation – Experimental Devices
- graphite pellet
containing the catalyst put
in an inert gas filled quartz
tube;
-oven maintained at a
temperature of 1,200 ◦C;
-energy of the laser beam
focused on the pellet;
-vaporize and sublime the
graphite
Sketch of an early laser vaporization apparatus
The carbon species are there after deposited as soot in different regions:
water-cooled copper collector, quartz tube walls.
2 Synthesis with CO2 laser
Vaporization of a target at a
fixed
temperature
by
a
continuous CO2 laser beam (λ =
10.6μm). The power can be varied
from 100Wto 1,600 W.
The synthesis yield is controlled
by three parameters: the
cooling rate of the medium
where the active, secondary
catalyst particles are formed,
the residence time, and the
temperature (in the 1,000–
2,100K range) at which SWNTs
nucleate and grow.
Fig. 3.10 Sketch of a synthesis reactor with a
continuous CO2 laser device
3 Electric-Arc Method – Experimental Devices
After the triggering of the arc
between two electrodes, a
plasma is formed consisting
of the mixture of carbon
vapor, the rare inert gas
(helium or argon), and the
vapors of catalysts.
The vaporization is the
consequence of the energy
transfer from the arc to the
anode made of graphite
doped with catalysts.
Sketch of an electric arc reactor. It consists
of a cylinder of about 30 cm in diameter
and about 1m in height.
Electric-Arc Method – Experimental Devices
• In view of the numerous results obtained with this electric-arc
technique, it appears clearly that both the nanotube
morphology and the nanotube production efficiency strongly
depend on
• the experimental conditions and, in particular,
• on the nature of the catalysts.
4 Solar energy reactor
Sketch of a solar
energy reactor in use
in Odeilho (France).
(a) Gathering of sun rays,
focused in F;
(b) Example of Pyrex®
chamber placed in (a)
so that the graphite
crucible is at the
point F.
The high temperature of about 4,000K permits both the carbon and the catalysts
to vaporize. The vapors are then dragged by the neutral gas and condense onto
the cold walls of the thermal screen.
Application:
Nanotube-based SPM (scanning probe microscopy) tips
Fig. 3.27 Scanning electron microscopy
image of a carbon nanotube (MWNT)
mounted onto a regular ceramic tip as a
probe for atomic force microscopy.
Small diameters of SWNTs were
supposed to bring higher resolution
than MWNTs due to the extremely short
radius of curvature of the tube end. But
commercial nanotubebased tips use
MWNTs for processing convenience.
Application: Efficient Field Emitters
The electrons are taking out
from the tips and sent onto
an electron sensitive screen
layer.
Replacing
the
glass
support and protection of
the screen by some
polymer-based material will
even allow the develop of
flexible screens.
Fig. 3.28 (a) Principle of a field-emitter-
based screen. (b) SEM image of a
nanotube-based emitter system (top
view). Round dots are MWNT tips seen
through the holes corresponding to the
extraction grid.
The first commercial
flat TV sets and computers using
nanotube-based screens are
about to be seen in stores.
(Motorola, NEC, NKK, Samsung,
Thales, Toshiba, etc.)
Application: Chemical Sensors
(a) Increase in a single
SWNT conductance when
20 ppm of NO2 are added
to an
argon gas flow.
(b) Same with 1% NH3
added to the argon
gas flow
Fig. 3.29a,b Demonstration of the ability of SWNTs in detecting
molecule traces in inert gases.
Fig. 3.30 Transmission electron microscopy image showing
rhodium铑 nanoparticles supported on MWNT surface