Carbon Nanotubes (CNTs)

Class: Material Science Engineering
Student : Hoang Van
Hanoi
Tien -2012


DID YOU KNOW?
 Carbon nanotubes, composed of interlocking

carbon atoms, are 1000x thinner than an
average human hair – but can be 200x
stronger than steel.


outline
 Definition
 Theory and properties
 Synthesis
 Potential and current applications
 Challenges and future


What are carbon nanotubes
CNT: Rolling-up a graphene sheet to form a tube

Schematic
of a CNT

STM image
of CNT
4

 Carbon nanotubes are hexagonally shaped

arrangements of carbon atoms that have
been rolled into tubes.
 These tiny straw-like cylinders of pure carbon
have useful electrical propeties. They have
already been used to make tiny transistor and
one-dimentional copper wire


Types of CNTs
 Single Wall CNT (SWCNT)
 Multiple Wall CNT (MWCNT)
 Can be metallic or semiconducting

depending on their geometry.


Single- walled
-Most single-walled
nanotubes (SWNTs)
have a diameter of cloes
to 1 nanometer,with a
tube length that can be
many millions of time
longer
-The structure of a
SWNTs can be

conceptualized by
wrapping a one-atomthick layer of graphite
called graphene in to a
seamless cylender


If:
m=0 , the nanotubes are called zigzag
n=m ,the nanotubes are called armchair
Otherwise ,they are called chiral


Multi-walled
 Multi-walled nanotubes (MWNTs) consist of

multiple rolled layer( concentric tubes) of
graphene

Triple-walled
armchair CNTs


 In the Russian Doll model, sheets of graphite are

arranged in concentric cylinders, e.g., a (0,8) singlewalled nanotube (SWNT) within a larger (0,17) singlewalled nanotube.
 In the Parchment model, a single sheet of graphite is
rolled in around itself, resembling a scroll of parchment
or a rolled newspaper.
 The interlayer distance in multi-walled nanotubes is
close to the distance between graphene layers in

graphite, approximately 3.4 Å. The Russian Doll structure
is observed more commonly. Its individual shells can be
described as SWNTs, which can be metallic or
semiconducting.


compare
 Single –walled CNTs exhibit electric

properties that are not shared by the multiwalled CNTs variant
 SWNTs is useful in the development of the
first intramolecular field effect transistors
(FET)


torus
-Torus is theoretically described
as carbon nanotube bent into a
torus (doughnut shape) .
-Nanotorus are predicted to
have many unique properties
such as :
+magnetic moments
+thermal stability …
-Vary widely depending on
radius of the torus and the
radius of the tube


nanobud

 In nanotechnology,carbon nanobuds form a

material (discovered and synthesized in 2006)
which combines two previously discovered
allotropes of carbon: carbon nanotubes and
spheroidal fullerences (or, in short, fullerenes)

 fullerenes are covalently bonded to the outer

sidewalls of the underlying nanotube
=>>>> Has useful properties of both fullerenes and
carbon nanotubes


Extreme carbon nanotubes
-The observation of 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
single-walled carbon nanotubes.
-The shortest carbon nanotube is the
organic compound cycloparaphenylene
-The thinnest carbon nanotube is
armchair (2,2) CNT with a diameter of 3
Å. This nanotube was grown inside a
multi-walled carbon nanotube

-The thinnest freestanding single-walled
carbon nanotube is about 4.3 Å in
diameter


PROPERTIES OF
CARBON
NANOTUBES


Strength and elasticity
 CNTs are expected to be the

ultimate high-strength filber
 Single wall carbon nanotubes
are stiffer than steel and are
very resistant to damage
from physical forces
 Carbon Nanotubes (CNTs)

very useful as probe tips for
very high-resolution scanning
probe microscopy.


elasticity
-The current Young’s modulus value of single walled
carbon nanotubes is about 1 terapascal
-The modulus of the multi walled carbon nanotubes
correlates to the amount of disorder in the carbon

nanotube walls
-when multi walled carbon nanotubes break, the
outermost layers break first


Comparison of mechanical
properties
Materials
Young’modulus(Tpa)
Tensile
strength(Gpa)

Elongation at
break(%)

SWNTE

~1 (from 1 to 5)

13-53

16

Armchair
SWNTT

0.94

126.2

23.1

Zigzag SWNTT

0.94

94.5

15.6-17.5

Chiral SWNT

0.92

MWNTE

0.2-0.8-0.95

11-63-150

Stainless steelE

0.186-0.214

0.38-1.55

15-50

Kevlar-29&149E

0.06-0.18

3.6-3.8

~2

Experimental observation;

E

T

Theoretical prediction


Electrical properties
 For a given (m,n)

nanotubes:
 If n=m(armchair) the
CNTS is metalic
 If n-m is multiple of 3
,the CNTs is
semiconducting with a
small band gap
 Otherwise ,the CNTs is
moderates
semiconductor

Thermal property
 All nanotubes are expected to be very good thermal

conductors along the tube, exhibiting a property known
as "ballistic conduction ", but good insulators laterally to
the tube axis.
 SWNT has a room-temperature thermal conductivity
along its axis of about 3500 W·m−1·K−1.
 in copper : 385 W·m−1·K−1
 A SWNT has a room-temperature thermal conductivity
across its axis (in the radial direction) of about 1.52
W·m−1·K−1. (same as oil)


defect
 As with any material, the existence of a

crystallographic defect affects the material
properties.
 Because of the very small structure of CNTs, the
tensile strength of the tube is dependent on its
weakest segment in a similar manner to a chain,
where the strength of the weakest link becomes
the maximum strength of the chain.
 Crystallographic defects also affect the tube's
electrical properties and thermal properties.


Toxicity .
 Under some conditions ,nanotubes can cross

membrane barriers ,which suggests that if raw
materials reach the organs, they can include
harmful effects such as inflammatory and
fibrotic reactions
 CNTs were capable of
producing
inflammation, epithelioid
granulomas (microscopic nodules), fibrosis, and
biochemical/toxicological changes in the lungs
 =>>>carbon nanotubes can pose a serious risk to
human health


synthesis
Techniques have
been developed
to produce carbon
nanotubes in
sizeable quanlities
,some of them are:
- Arc discharge
- Laser ablation
- Chemical vapor
deposition(CVD)


Arc discharge
 Nanotubes were observed in 1991 in the carbon

soot of graphite electrodes during an arc
discharge, by using a current of 100 amps , that
was intended to produce fullerenes.
 the carbon contained in the negative electrode
sublimates because of the high-discharge
temperatures.
 The yield for this method is up to 30% by weight
and it produces both single- and multi-walled
nanotubes with lengths of up to 50 micrometers
with few structural defects