Carbon Nano tubes and its Applications in the Field of Electronics and Computer Science

IJSRD - International Journal for Scientific Research & Development| Vol. 2, Issue 09, 2014 | ISSN (online): 2321-0613
All rights reserved by www.ijsrd.com 237
Carbon Nano Tubes and its Applications in the Field of Electronics and
Computer Science
Pawan Patidar1
Kapil Kasera2
Mukesh Kumar Vijay3
Prateek Diwan4
1,3,4
Assistant Professor 2
Engineer (Thermal Power Plant)
1,3,4
Vivekananda Institute of Technology, Jaipur, Rajasthan, India 2
Grasim Industries Ltd, India
Abstract— With rapid advancement of technology and
unlimited quest in the intricate fields of science led man to
confront nano tubes. It consists of C60 Fullerenes with tube
like structures capped at both ends delivering extraordinary
mechanical and electrical properties. It is hard to stress as
extremely low turn on for fields and has high current
densities. It is also the best emission field emitter for future
field emission displays. Can be extensively used for fuel
cells and field emission display. We throw a light on the
research on nano tubes and it’s general applications. In this
paper we are focusing and questioning the field of research
to ponder for the betterment off life to nano tube.
Key words: Nano tube, Single Electron Transistor, Carbon
vapour deposition, Nano-electronics, Super capacitors, Nano
probe and sensor
I. INTRODUCTION
Carbon nano tube (CNT) is a new carbon allotrope that was
first discovered in 1991 by Dr. Sumio Iijima at NEC. CNT
has closed tubular structures consisting of nested cylindrical
graphite layers capped by fullerene-like ends with a hollow
internal cavity. Carbon nano tube should not be confused
with Carbon fibers: In CNTs walls are well graphitized and
are parallel to the axis. We can imagine a sheet of graphite
(carbon atoms disposed in a honeycomb lattice, graphene)
rolling up to form a cylinder. These cylindrical structures
are called Carbon Nano tubes. These elongated cylindrical
structures ranges from one to several tens of nanometers in
diameter and up to several micrometers in length. They can
be looked at as single molecules, regarding their small size
or as quasi- dimensional crystals with traditional periodicity
along their tube axis.
Carbon nano tubes are formed from pure carbon
bonds. Pure carbons only have two covalent bonds: sp2
and
sp3
, the former constitutes graphite and the latter constitutes
diamond.
Figure: Structure of graphene sheet
Figure shows the structure of graphite and
diamond.sp2
is a strong bond within a plane but weak
between planes. sp2 is composed of one s-orbital and two p-
orbitals. When more sp2
bonds come together, they form
six-fold structures, like honeycomb pattern, which is the
plane structure, the same structure as graphite. Graphite is
stacked layer by layer so it’s only stable for one single sheet.
That’s why graphite is used in pencils. Viewing these layers
perpendicularly shows the honeycomb patterns of graphite.
Wrapping these patterns back on top of themselves, joining
the edges, and close one end while leave one end open, we
form a tube of graphite, which is a Nano tube.
II. STRUCTURE OF CNT
In general the nano tubes could be specified in terms of the
tube diameter (d) and the chiral angle (ø). The chiral vector
(ch) is defined as a line connected from two crystallographic
ally equivalent size on a two dimensional grapheme
structure. The chiral vector can be defined in terms of the
lattice translation indices (n, m) and the basic vectors a1 and
a2 of the hexagonal lattice .i.e. ch = na1+ ma2
The chiral angle (ø) is measured as an angle
between the chiral vector ch with respect to the zigzag
direction (n, 0), where ø = 0° and the unit vectors of a1 and
a2. The armchair nano tubes is defined as the ø= 30° and the
translation is (n,n). All other types of nano tubes can be
identified as pair of indices (n, m) where n≠m.
Figure: Vector notation of CNT
III. TYPES OF CARBON NANO TUBE
There are two types of nano tubes existing in nature: single-
wall nano tube and multi-wall nano tube. Figure show the
structure of single-wall nano tube and multi-wall nano tube.
A tube made of a single graphite layer rolled up into a
hollow cylinder is called a single-walled nano tube
(SWNT); a tube comprising several concentric arranged
cylinders is referred to as a Multiwall nano tube (MWNT).
Multiwall nano tubes have similar lengths to single walled
nano tubes, but much larger diameters. Their inner and outer
diameters are around 5 and 100nm respectively
corresponding to 30 coaxial tubes. Confinement effects are
expected to be less dominant in MWNT than in SWNT
because of larger circumference. Many of the properties of
multiwall tubes are already quite close to graphite. While,
the multiwall nano tubes have wide range of applications,
they are less well defined from their structural and hence
electronic properties due to many possible numbers of
layers.

Carbon Nano Tubes and its Applications in the Field of Electronics and Computer Science
(IJSRD/Vol. 2/Issue 09/2014/055)
The properties of SWNT are more stable than
MWNT so it is more favorable. SWNT have better defined
shapes of cylinder than mwnt, thus mwnt has more
possibilities of structure defects and its nanostructure is less
stable. Hence, nano tubes are one-dimensional objects with
a well-defined direction along the nano tube axis that is
analogous to the in-plane directions of graphite Most
researchers focus on SWNT and develop applications based
on SWNT due the physical stability of SWNT.
Fig.: Structure of SWNT and MWNT
IV. PROPERTIES OF NANO TUBES
Carbon nano tubes have attracted attention primarily
because of their unique structure, and their exotic
mechanical, thermal, chemical, and electronic properties
A. Mechanical Properties
Two mechanical properties are considered to be important,
the stiffness or elastic strength and the tensile strength of the
material. The reported value of Young’s Modulus for CNTs
goes up to 1.26TPa, which is 5 times greater than steel (230
GPa) and tensile strength up to 63Gpa. That means that
materials made of nano tubes are lighter and more durable.
The chart compares the tensile strength of SWNT's
to some common high-strength materials.
B. Electronic Properties
Carbon nano tubes have some distinct electrical properties.
One of the important properties of carbon nano tube is that it
can exhibit the characteristics of a metal or a semiconductor.
Specially, the energy gap is determined by the rolling
direction of nano tube. . There is a simple rule to determine
if the nano tube acts as a metal or a semiconductor: if
(n+m)/3 = integer, nano tube acts as a metal otherwise it acts
as a semiconductor. Here chiral vector is denoted by a pair
of integers (n, m).
C. Thermal properties
The thermal conductivity of carbon nano tubes is dependent
on the temperature, current and vacancy concentration. The
thermal conductivity of CNTs (2000W/mK) is five times
greater than that of copper (400W/mK).
D. Chemical properties
Carbon nano tubes are very strong against acid and high
temperature because of their perfect conjugated system.
Acid and heat are often applied to purify carbon nano tubes.
SWNTs are capable of adsorbing hydrogen at ambient
temperature and pressure.
V. SYNTHESIS OF CNT
Primary synthesis for SWNT and MWNT include arc
discharge, laser ablation etc. Along with gas phase catalytic
growth, such as CVD offer greater potential for the scaling
up of nano tube production. In electric arc discharge
technique, the carbon arc provides a simple tool for
generating the temp. needed for the vaporization of carbon
atoms in a plasma (>3000°C, electrodes of 50-20 mm dia,
20-25 V across electrode and a DC of 50-120 amps flowing
in between). Once the arc is in operation, the carbon
deposits on the negative electrode. For MWNT, no catalyst
is used while for SWNT, the electrodes are doped with a
small amount of metallic catalyst impurity.
Laser ablation employs sequence laser pulses to
vaporize a target containing graphite mixed with small
amount of Co and Ni. Flowing Argon gas sweets the trapped
nano tubes from high temperature zone to cooled collector.
High yields with >70-90% were reported in the condensing
of the heated flow tube.
A. Limitations
Scaling off cannot be done due to size of the carbon source
(Anode in arc discharge and graphite target in laser
ablation). It also requires subsequent purification steps to
separate amorphous carbon and non-tubular substances. Due
to them gas phase techniques such as chemical vapor
deposition has been motivated. Gas phase growth of SWNT
by using carbon monoxide finds highest yields at highest
conditions (1200°C, 10 atm). At some places hydrocarbons,
acting as carbon source, pyrolize readily on surfaces heated
above 600-700°C. CVD methods have been successful to
produce the vertically aligned CNTs in large quantities and
at relatively low temperature. It occurs at 550°C on Ni
coated Si substrate placed parallel to Pd plates as a dual
catalyst and a tungsten wire filament. The CNT length
increases with the increase in gas flow. Ni-C solid solution,
which enables the carbon atoms to diffuse more easily even
at low temperatures. The diameter and density of the aligned
CNTs are determined by the thickness of the metal films
while the length of the tubes can be controlled by varying
the CVD reaction time. The CNTs were selectively
deposited on the pattern Ni catalyst layer, which is sputtered
on Si substrate. Morphology of the nano tubes is strongly
influenced by the flow ratio of methane to hydrogen. Defect
less nano tubes with small diameters are favorably produced
under a small flow ratio.

Image of CVD set-up (developed at SSPL.Delhi)
Carbon nano tubes have attracted interest due to
there high mechanical strength, hydrogen storage and
electron field emitting. In this context, the primary issue is
the scale of synthesis and the control of carbon
nanostructures
VI. APPLICATIONS
A. Applications in Fuel Cell Technology:
Carbon Nano tubes have been suggested for use in Fuel Cell
applications,. Carbon nano tubes are anticipated to play a
major role in next generation electronic components
inclusive of fuel cells. They offer significant advantages
over many existing materials due to their exceptional
mechanical, electronic and chemical properties.. The
efficiency of fuel cells is determined by the electron transfer
rate at the carbon electrodes, which is the fastest on nano
tubes
B. Electrochemical Super Capacitors
Super capacitors have a high capacitance and potentially
applicable in electronic devices. Typically, they are
comprised two electrodes separated by an insulating
material that is ironically conducting in electrochemical
devices. The capacity of an electrochemical super cap
inversely depends on the separation between the charge on
the electrode and the counter charge in the electrolyte.
Because this separation is about a nano meter for nano tubes
in electrodes, very large capacities result from the high nano
tube surface area accessible to the electrolyte.
C. Field emitting devices
If a solid is subjected to a sufficiently high electric field,
electrons near the Fermi level can be extracted from the
solid by tunneling through the surface potential barrier. This
emission current depends on the strength of the local electric
field at the emission surface and its work function (which
denotes the energy necessary to extract an electron from its
highest bounded state into the vacuum level). The applied
electric field must be very high in order to extract an
electron. This condition is fulfilled for carbon nano tubes,
because their elongated shape ensures very large field
amplification. For technological applications, the emissive
material should have a low threshold emission field and
large stability at high current density. Furthermore, an ideal
emitter is required to have a nanometer size diameter, a
structural integrity, a high electrical conductivity, a small
energy spread and a large chemical stability. Carbon nano
tubes possess all these properties. However, a bottleneck in
the use of nano tubes for applications is the dependence of
the conductivity and emission stability of the nano tubes on
the fabrication process and synthesis conditions.
D. Transistors
The field-effect transistor – a three-terminal switching
device – can be constructed of only one semiconducting
SWNT.
E. Top-gated field effect transistor.
By applying a voltage to a gate electrode, the nano tube can
be switched from a conducting to an insulating state.73 A
schematic representation of such a transistor is given in
Figure 4-1. Such carbon nano tube transistors can be
coupled together, working as a logical switch, which is the
basic component of computers.
Fig.: A single semi-conducting nano tube is contacted by
two electrodes. The Si substrate, which is covered by a layer
of SiO2 300nmthick, acts as a back-gate.
F. Single electron transistor:
Due to the ability to define nano-scale regions of p or n
material on a SWNT scientist have been able to make such a
small quantum dot (QD). The properties of such a small
doped region are influenced by the quantum mechanical
effects of a single electron, The single-electron tunneling
(SET) transistor consists of a gate electrode that electro
statically influences electrons traveling between the source
and drain electrodes. The electrons in the SET transistor
need to cross two tunnel junctions that form an isolated
conducting electrode called the island. Electrons passing
through the island charge and discharge it, and the relative
energies of systems containing 0 or 1 extra electrons depend
on the gate voltage. At a low source drain voltage, a current
will only flow through the SET transistor if these two charge
configurations have the same energy
G. Nano probes and sensors
Because of their flexibility, nano tubes can also be used in
scanning probe instruments. Since MWNT tips are
conducting, they can be used in STM and AFM instruments.
Advantages are the improved resolution in comparison with
conventional Si or metal tips and the tips do not suffer from

crashes with the surfaces because of their high elasticity.
However, nano tube vibration, due to their large length, will
remain an important issue until shorter nano tubes can be
grown controllably. Nano tube tips can be modified
chemically by attachment of functional groups. Because of
this, nano tubes can be used as molecular probes, with
potential applications in chemistry and biology.
Fig.: Use of a MWNT as AFM tip. VGCF stands for Vapor
Grown Carbon Fibre. At the centre of this fibre the MWNT
forms the tip.
H. Computer Memory:
One of several revolutionary methods of building futuristic
computers involves carbon nano tubes. At Harvard
University, A small jolt of electric current bends the top of
one nano tube down to meet another and a nano-switch is
formed --a switch somewhere in the neighborhood of 100
times smaller than those in current state of the art
computers. {The smallest features possible with today's
photolithography are about 125 nanometers wide.} In
principle-Arrays of these switches could be connected to
form a logic circuit that would enable a computer to operate
incredibly faster and more efficiently-combining ultra-fast
computing power with extremely low electrical
requirements. Basically all the information on your current
hard drive, AND the computer itself could be compressed
into a Dick Tracy style wrist watch. A billion bits of data
storage on a chip slightly larger than a freckle.
VII. CONCLUSIONS
Carbon nano tubes have been utilized either individually or
as an ensemble to build functional device prototypes, as has
been demonstrated by many research groups. Ensembles of
nano tubes have been used for field emission based flat
panel displays, composite materials with improved
mechanical and electromechanical actuators. Bulk quantities
of nano tubes have also been suggested for high capacity
hydrogen storage media. Individual nano tubes have also
been used for field emission sources. Tips for scanning
probe microscopy, nano tweezers and chemical sensors.
Nano tubes are also promising as the central elements for
future miniaturized electronic devices. The successes in
nano tubes growth has led to the wide availability of nano
tubes material, which is a main catalyst behind resent leaps
and bounds in basic physics studies and applications of nano
tubes.
REFERENCES
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Huffman D R , Nature , 347 (1990) 354.
[4] Ebbesn T W & Ajayan PM, Nature , 358
(1992)
[5] Singh Charanjeet , Shaffer Milo S P & Windle
Alan H , Carbon , 41 (2003) 359.
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H M , Science 286 (1999) 45
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