1
MODULE-2
CHAPTER-2
SUPERCONDUCTIVITY
Introduction
The field of superconductivity has emerged as one of the most exciting fields of
solid state physics and solid state chemistry in the last decades. The
phenomenon of superconductivity is first observed by KammerlinghOnnes in
1911. The theoretical explanation of superconductivity is first given by
Bardeen, Cooper, Schriefer in 1957 and is called BCS theory
Experimental Demonstration
Helium gas was liquefied by Heike KamerlinghOnnes in 1908. The boiling point
of liquefied Helium is 4.2K. He studied the properties of metals by lowering
their temperature. At normal temperature all metal posses electrical resistivity
which limits the current flow through them. In 1911, he studied the electrical
properties of mercury at low temperature. He found that when Mercury was
cooled to the boiling point of Helium (4.2 K) its electrical resistancecompletely


1
   ,   0,   


itindicates that mercury gets transformed from one conducting states to
another. This property is said to be superconducting property. The materials
those are exhibiting the superconducting property are ‘superconductors’. The
temperature at which materials gets transformed from one conducting states to
another state.
vanishes abruptly.ie, its conductivity (
2
The transition temperature are different for different conductors. The
phenomenon of superconductivity depends on temperature, magneticfield,
atomic structure etc. This phenomenon was observed in many materials
Lead (Pb), TC = 7.2K
Tin (Sn), TC = 3.7K
Aluminium(Al), TC=1.2K
“ The Process of loss of resistance of certain materials when cooled below
certain specific temperature is called Superconductivity and materials showing
this property are called Superconductors”.
“The minimum temperature to which material must be cooled so that its
resistance becomes just zero is called critical temperature Or Superconducting
transition temperature”.
After the invention of superconducting property in mercury, several
materials were tested for superconductivity. Good electrical conductors at room
temperature . Such as gold, copper and silver are not good superconductors.
The materials with high resistivity at room temperatures generally found to be
good superconductors.
High Temperature Superconductors
Conventional Superconductors have their TC <23K.
The Superconductors those having the TC higher than conventional
superconductors are said to be High temperature Super conductors. They are
not metal or intermetallic compounds at all but they are oxides.
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Properties of Superconductors
1. CRITICAL TEMPERATURE
The temperature at which electrical resistance of a metal
drops to zero is called the critical temperature (Tc) and this temperature
is a characteristic of the material. Some examples are: Zinc
-0.88 K
Aluminium – 1.2 K
Mercury
-- 4.2 K
2) Electrical resistivity(ρ) Or Zero electrical resistance
The electrical resistivity of the superconducting material is zero.
The scientist have studied the current flowing through a
superconducting solenoid for a period of nearly three years. They found
that there is no change in the current of the material. It represent the
resistivity of the material is zero in the superconducting state. In a
normal conducting material, if a small amount of current is applied, it
will be destroy with in 10-12sec due to resistance loss(loss= i2R).
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3) Persistant Currents
An electrical current can be induced in a superconducting ring by
the principle of electromagnetic induction.
Consider a superconducting material in the form of a closed ring placed
in an external magnetic field. When the ring is cooled from a temperature
above the transition temperature TC to a temperature below TC , a
current is induced in it . When an external magnetic field is cut off, this
induced current remains in the ring for a long period without any
decrease in intensity. In an ideal case this current will persist forever
without
any
change.
Such
electric
currents
remaining
in
superconducting ring for a very long period without any decrease in
strength are called persistant current.
Experimentally it is proved that a lead ring carried several
hundred amperes of current for more than one year without any
decrease.If the ring had finite resistance R, the current circulating in the
ring would decrease according to the relation I (t )  I 0 e
I(t)
Current after a period ‘t’
L
Length
R
Resistance in the superconducting state.
In the superconducting state, R=0
I(t)=I(0)
4) Diamagnetic Property
The Flux Expulsion : The Meissner Effect
 Rt
L
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Consider a magnetic field applied to a normal conducting material. The
magnetic lines of forces penetrate through the material. Consider that a
normal conductor is cooled down to very low temp. for superconducting
property. If it is cooled down below the critical temperature, then the
magnetic lines of forces are ejected from the material. A diamagnetic
material also repels the magnetic lines of forces, so the ejection of
magnetic lines of force when the superconducting material is cooled
down is said to be the diamagnetic property. This property was first
discovered by Meissner and hence this property is also called “Meissner
effect”.
The property by which magnetic flux density is completely expelled from
the interior of a superconducting material during the transition from
normal state to superconducting state is called Meissner effect.
The magnetic flux density
B=µ0(M+H)
For a Superconducting material, B=0
Sub B=0 in eq(1)
Eq(1)
0=µ0(M+H)
(M+H)= 0
M=-H
(1)
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M
H
H

 1
H

Where M is the intensity of magnetization due to
applied magnetic field H.
The negative value of susceptibility shows thediamagnetic properties of
the superconducting material.
If a specimen of superconductor is placed in a strong M.F, the
specimen loses its property of superconductivity and become normal
material as shown in fig.
  1 , This is the maximum value of susceptibility of a perfect
diamagnet. Hence the superconductor become perfect diamagnet at
transition temperature.
When a superconductor is cooled below the transition
temperature in the presence of an external field, a persistant current is
developed on the specimen in a direction opposite to the applied
field.This cancel the applied field and the specimen behaves as a perfect
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diamagnet. Here super conductivity produces entirely a new type of
strong diamagnetism which opposes and repels the external magnetic
field. This leads to a levitation property. Magnetic levitation principle is
made use of in many cases like maglev coaches in railway, ship-drive
system, magnetic propulsion of satellites etc.
Conversely if the superconducting specimen is heated from a very low
temperature to a temperature above the transition temperature. It loses
its diamagnetic property, and magnetic lines of force begins to penetrate
through the specimen . Thus above the transition temperature it returns
to its normal conducting states. Hence Meissner effect is reversible. This
is the experiment to prove that a superconductor is a perfect
diamagnetic.
Zero resistivity and perfect diamagnetism are the two independent
essential properties of the superconducting state.
Let us consider a superconducting material under
normal state. Let ‘J’ be the current passing through the material of
resistivity ‘ρ’. From ohm’s law,
E=Jρ
On cooling the material to its transition ‘ρ’ tends to zero. If ‘J’ is held
finite ‘E’ must be zero. From Maxwell’sequqtion
dB
 E  
dt
Under superconducting condition since E=0
dB
 0 Or B=constant.
dt
This means that the magnetic flux passing through the specimen should
not change on cooling to the transition temperature. The Meissnereffects
contradicts this result. According to Meissner effect perfect
diamagnetism is an essential property of defining the superconducting
state.
Thus
from zero resistivity E=0
fromMeissner effect B=0
5) Effect of Magnetic field on Superconductivity and
Critical field
Superconductivity of a material depends on the
temperature and magnetic field. i.e, superconducting property of a
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material can be destroyed by increasing the strength of M.F Or by
increasing temperature Or by increasing both. So material can exhibit
super conducting property only if its temperature and magnetic field are
below certain critical values.
Consider a superconductor maintained at temperature less
than TC. If a magnetic field of sufficient magnitude is applied parallel to
the length of superconductor then superconductivity can be destroyed
even though temperature is still less than TC. Thus original resistance of
the wire gets restored and it starts behaving like a normal conductor.
“ The minimum value of magnetic field at a given temperature, that must
be applied across that material so that it losses Superconducting
bahaviour is called Critical magnetic field” and it is denoted by HC.
Or
“ Maximum field in which a superconductor remains in superconducting
state”.
Critical field is a function of temperature. It decreases with increase in
temperature and T= TC , HC become zero. Graph b/w HC and temp. T is
shown in fig for various substances. The variation is parabolic in nature.
 T2 
H C (T )  H C (0) 1  2 
 TC 
Where HC(0) is the value of critical field at 0K. It has a
specific value for each material. This diagram may be realized as a Phase
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diagram. The lower left region of the graph represents superconducting
state and upper right region represents normal conducting state.
6)Crtitical Current
When current is passed through a conductor it produces a
magnetic field. If the magnetic field produced due to current is more than
critical magnetic field ‘HC’ the superconducting state of the material may
be destroyed even there is no external magnetic field around the
conductor. This limits the maximum amount of current that can be
passed through a superconductor. This maximum allowable current is
called critical current IC.
Consider a superconducting solenoid carrying current
Let
r = radius of superconducting wire Or Cylindrical Specimen.
I = Current Passed.
B = Magnetic Flux density at the surface of the wire.
H = Magnetic Field at the surface of the wire.
There fore,
 I
B 0
2r
(1)
B
I
H

 0 2r
When I= IC =critical current
Then H=HC, critical Magneticfield.
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HC 
There foreeq(1)
IC
2r
Or
I C  2rH C
This eq. is called Silsbee’s Rule. Silsbee suggested that the important factor in
causing destruction of superconductivity was the magnetic field associated
with currents rather than the value of current itself. Thus destruction of
superconductivity is actually field controlled effect.
7) Critical Current density
The magnetic field which destroys superconductivity, need not be necessarily
the external applied field, but it may be the field produced as a result of
current flow in the superconducting ring itself. Even if the field produced by
itself exceeds HC, the superconductivity of the ring is destroyed .Thus ,if a
superconducting material carried a current and if the magnetic field produced
by this current is equal to HC,the superconductivity disappears. The maximum
current density J at which the superconductivity disappear is called the critical
current density JC. For any value of J< JC, the current can sustain itself where
as for values of J> JC, the current cannot sustain itself. This effect was
discovered in 1916 by Silsbee and is known as Silsbee effect.
JC 
IC
A
Where A is the area.
Or
Critical current density is the minimum current density below which the
material is in its superconducting state and above which it is in its normal
conducting state.
9) Isotope Effect
superconducting critical temperature for various isotopes of a superconductor
is different. This effect is known as Isotope effect.
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In 1950, C.A Reynold and E. Maxwell found that the critical
temperature decreases with increasing isotopic mass M. It is given by the
relation.
TC
M-1/2
TC = a constant
M1/2
M1/2TC= Constant
Where M= Isotopic Mass, TC = Critical Temperature in Kelvin.
Eg: As average isotopic mass of mercury varies from 199.5 t0 203.4 a.m.u, the
value of TC changes from 4.185 K to 4.146 K.
10) Energy Gap Or Superconducting Energy Gap
Any process taking place naturally is accompanied by release of energy and
this give more stability to system. When a superconducting specimen is
maintained at temperature less than TC, its resistance becomes zero naturally.
It means that at temperature less than TC, its resistance becomes zero
naturally. It means that at temperature T<TC the superconducting state is
accompanied by release of finite amount of energy. In order to destroy
superconductivity this energy given back to specimen externally. Thus the
energy states of specimen in the superconducting state are separated by a
finite gap from energy states of normal state. The lower states are
superconducting states and higher states are normal states. With rise of
temperature the energy gap decreases and above TC the enrgy gap is destroyed
and resistance of materials becomes non zero.
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At absolute 0K, all electrons are superconducting and at temperature above 0K
some normal states are also filled.
This band diagram is different from that of insulators and semiconductors
in the following ways.
1) In insulators the lower band is called valence Band and upper band is
called Conduction band. Electron in conduction band are free and can
take part in conduction while electrons in valance band are not free and
cannot conduct. However in superconductors electrons in Normal as well
as superconducting band are conducting electrons. The only difference is
that normal electrons shows resistance and superconducting electrons
donot show resistance.
2) The energy gap of superconductors depends on temperature . With
increase in temperature it decreases and becomes zero at temperature
TC. However energy gap of insulators is nearly independent of the
temperature.
The existence of energy gap in superconductors has been confirmed by a
number of experiments. Theoretical value of the energy gap of specimen
at 0K
Eg = 2∆= 2bkbTC
Here∆=bkbTC, is called energy gap parameter. ‘b’ is a constant, normally b
≈1.4. The energy gap is related to Fermi energy as
Eg≈10-4 EF
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12) Flux quantization
A closed superconducting loop can enclose magnetic flux only in
integral multiples of a fundamental quantum of flux Or The
magnetic flux that passes through a superconducting ring ( or a
hollow superconducting cylinder) is quantized in the order of
h/2e. This phenomenon is said to be flux quantization.
by
n
h
2e
  n 0
n= 1,2,3……
Where  0 
h
2e
Is the flux quantum and is called fluxon Orfluxoid. The value of flux quantum is
0  2.07  10 15 Weber
The quantization of magnetic flux has been confirmed experimentally in 1961
by Deaver and Fairbank. The Quantization of magnetic flux is a special
property of superconductors. The magnetic flux produced in an ordinary
transformer Or solenoid coil is not Quantized.
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13))
Thermal Property

Entropy
Entropy is a measure of the disorder of a system. In all
superconductors the entropy decreases significantly on cooling below
the critical temperature TC. Therefore the observed decrease in entropy
b/w the normal state and superconducting states shows that the
superconducting state is more ordered than normal state. For
aluminium, the change in entropy was observed to ba small of the
order of 10-14kB/atom, where kB is the Boltzmann constant. The
variation of entropy of aluminium in the normal and superconducting
states with temperature is shown in fig.

Specific heat
The specific heat capacity of superconducting material has some
discontinuity at the critical temperature. The specific heat capacity of
Tin is 3.72 K. A discontinuity of specific heat occurs at the critical
temperature. The discontinuity is due to the absence of the magnetic
field at T=TC.
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Type I and Type II Superconductors
Superconductors are classified into type I( soft) and type II( hard)
depending upon their magnetization behavior in an external magnetic
field.
Type I( Soft) Superconductors
When a superconductor is placed in an external magnetic field,
magnetism is induced in it. Let H be the strength of the external
magnetic field and M be the intensity of magnetization induced in a
super conductor. Variation of intensity of magnetization ‘M’ with the
external field ‘H’ is represented graphically. Intensity of Magnetization
‘M’ increases linearly with the magnetic field ‘H’. Since the flux density
inside the material is zero, H= -M . Negative sign shows that it is
diamagnetic .i.e, Magnetic lines of force are expelled from the specimen
and it behaves as a diamagnetic since there exists a repulsive force
inside it. This continued until the external magnetic field increases to
the critical field HC.
b) Plot of H versus M for Type I superconductors
When magnetic field H=HC the intensity of magnetization
suddenly falls to zero value indicating that magnetic lines of force are
suddenly penetrating through the material since there is no repulsive
force in it. i.e, the material lost its superconducting property
completely. At H=HC, it regain its resistivity and it behaves as a normal
conductor. Up to HC, the specimen is a perfect diamagnet and it obeys
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Meissner Law strictly Such a superconductors for which the induced
magnetization suddently falls to zero value when H becomes equal to
the critical Field HC are called Type-I Superconductors.
The value of critical fieldfield is very low, in theorder of 0.1 T
to 0.2 T. This reveals that a very weak magnetic field can destroy the
superconducting property of type-I super conductors. Since the critical
field HC is very small, strong magnetic field can’t be produced and
maintained with this type of superconductors. Hence they have no
practical importance.
Properties
1. Transition from superconducting to the normal state is very
abrupt.
2. Critical field HC is very small in the order of 0.1 T.
3. Superconductivity can be easily destroyed.
4. At the critical field HC, the transition is reversible. i.e, when the
strength of magnetic field is reduced below HC, its
superconducting property is reinstated.
Uses
1. It can be used as a switching device.
2. It can be used as a superconducting magnetic shield and used in
occasions where a complete exclusion of magnetic field is required.
3. Since the HC is very small for those materials ,they can be used to
fabricate coils for superconducting magnets.
Examples
Almost all pure matals belongings to this group. Lead, tin, Hg, Al, Mg
etc. are best examples.
b) Type II Superconductors Or Hard Superconductors
When certain superconductors are placed in an external
magnetic field of strength H, magnetism is induced on the specimen.
The intensity of magnetization M induced in the superconductor
increases with the external field H, variation of M with H is shown
graphically.
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At first the intensity of magnetization increases linearly with the
magnetizing field ‘H’ as in the case of type –I superconductors. This is
continued upto the critical field HC1, called the lower critical field. In
this region there is a repulsive force in the specimen and hence
magnetic lines of force are expelled from the specimen. So it behaves
as a perfect diamagnet and it obey Meissner law strictly upto HC1.
When the strength of magnetizing field is increased beyond HC1, the
intensity of magnetization ‘M’ gets decreased very slowly. Repulsive
force in the specimen gets decreased, the magnetc lines of force begin
to penetrate through the specimen and the specimen loses its
diamagnetic property correspondingly. This is continued up to the
second critical field HC2 , called upper critical field at which the
magnetic forces have penetrated exclusively and the specimen loses
its diamagnetic property completely. i.e, Superconductors loses its
superconducting property completely and it is converted into its
normal conducting state. Beyond HC2, the material in its normal
conducting state. In the region b/w the lower critical field HC1 and
upper critical field HC2, the material still remains in superconducting
state. But magnetically it is in mixed state and this region is called
“vortex”. Here the material is practically diamagnetic and at the same
time lines of force are partially penetrating through it. It doesnot
strictly obey Meissner law strictly in this region. It is clear that
transitions from superconducting state to normal state is very slow,
gradual, and prolonged. The second critical field HC2 is larger and
hence a very strong magnetic field is required to destroy
superconducting property completely. So the type-II superconductors
are also called ‘ Hard Superconductors’. Large current flow through
type-II superconductors in vortex region.
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Properties
1. The transition from superconducting state to normal conducting
state is very slow and gradual.
2. There are two critical fields, lower critical field and upper critical
field.
3. There is a mixed state in between the two critical fields.
4. Upper critical field HC2 is very high in the order of 20T to 50T.
5. Very strong magnetic field is required to destroy the
superconducting property.
6. The transition is irreversible since there is hysteresis loss of
energy.
Uses
1. Very strong and powerful magnetic field can be produced and
maintained using Type-II superconductors. Such high magnetic
field is very essential in particle accelerators, fusion reactors and
in plasma production.
2. Strong magnetic field is used for the magnetic levitation
purposes.
3. They are used in power generators.
Examples
Niobium, Germanium, alloys like niobium-Zirconium, Niobium-Tin,
Niobium- Titanium, alloys of aluminium, vanadium Silicon etc.
Ceramic superconductors belonging to this group.
BCS THEORY
BCS theory of superconductivity was put forward by Bardeen,
Cooper and Schrieffer in 1957 and hence name as BCS theory. This
theory could explain many observed effects such as zero resistivity,
Meissner effect, Isotope effect etc. The BCS theory was based on the
advanced quantum concept.
1) Electron- electron interaction via lattice deformation
Let us consider an electron passing through the
lattice of positive ions. The electron is attracted by
neibhouring ions. It forms a positive ions core. ie, it imparts
a momentum to these ion core due to coulomb interaction.
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It means that ion starts vibration and hence phonon gets
excited.
Now consider a second electron which is subsequently
passing through the moving region of increased positive
charge density. It will experience an attractive coulomb
interaction and can absorb all momentum of vibrating
region. Under this situation, the vibration of ions are
stopped and hence the phonon is absorbed by this second
electron. So in this interaction, the momentum which was
imparted by the first electron is taken up by the second
electron and hence these electron undergo an interaction.
This interaction would be an attractive interaction because
exchange of momentum takes place via coulomb attraction
interaction, of course through phonon. According to BCS
theory under certain conditions this attractive interaction
overcomes the force of repulsion b/w the two electron.
Therefore, the electrons are loosely bounded together. This
pair of electrons is called COOPER PAIR.The interaction
process can be written in terms of the wave vector ‘k’ as
k1-q = k1` and k2+q=k2`
This gives
k1+k2=k1`+k2`
ie, the net wave vector of the pair is conserved. The
momentum is transferred b/w the electrons. The pair of
electron are known as cooper pair
k1Wave vector of first electron.
q
Virtual phonon
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[ Virtual phononwhich is emitted by first electron and is absorbed by
an electron k2
There fore k1`
k1-q , k2`
k2 + q]
Cooper Pair
A pair of free electrons coupled through a phonon is called
cooper pair. In a typical superconductor the volume of a given pair
encomposes as many as 106 other pairs . The motion of all cooper
pairs is same. The superconducting state is an ordered state of
conduction electrons. Cooper pair has a special property of sailing
smoothly among the lattice point without any collisions. They are not
scattered by the lattice points and hence there is no exchange of
energy. If an electric field is established, these electrons gains
additional kinetic energy. But they do not transfer this energy to the
lattice points and they ‘sail’ with the same energy. Since there is no
scattering and no transfer of energy the material does not possess
any resistance. This explainzero resistivity of super conductors or
infinite conductivity.
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Existence of energy gap
The energy of the pair of electrons in the bounded state( cooper
pair) is less than the energy of the pair in the free state. The energy
difference is called energy gap ( Eg = 2∆). The energy gap prevent the
pairs from breaking apart. The energy gap is a function of
temperature. Pairing is complete at T=0K and is completely broken at
a critical temperature. Energy gap is maximum at absolute zero (0K).
At T=TC pairing is dissolved and energy gap reduces to zero.
Normal And Superconducting Tunneling
Consider a thin layer of an insulating material of thickness 10A0 to
20A0 between any two metals as shown in fig. It is clear that
quantum mechanically electron can tunnel through the thin barrier
from one metal to the other until the chemical potential of electron in
both the metals becomes equal. If a potential difference is applied
across them the chemical potential of onr of them increases relative
to the other and the net result is that more electrons tunnel through
the insulating layer. The current-voltage relation across the tunneling
junction is observer to obey Ohm’s law at low voltages.
Josephson Effect
In 1962 B.D Josephson, while a postgraduate student
at Cambridge predicted that ‘Supercurrent” consisting of correlated
pairs of electrons can be made to flow across an insulating layer b/w
two conductors provided the gap is small enough. Such a junction is
called weak link.
Let us now consider a thin insulating layer is sandwiched b/w two
superconductors. The superelectron ( cooper pair) tunnel through the
insulating layer from one superconductor to another with out
dissociation, even at zero p.d across the junction. Their wave
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function on both sides are highly correlated. This is known as
Josephson effect.
D.C Josephson Effect
A d.c current flows across the junction in the absence of any electric
or magnetic field is called D.C Josephson effect.The magnitude of
current varies b/w I0 to –I0 according to the value of phase difference
0.
According to Josephson, when tunneling through the insulator it
0 b/w the wave functions of cooper
pairs on either side of the junction
The tunneling current is given by
I = I0
0)
Where I0 is the maximum current that flows through the junction
with out any p.d across the junction. I0 depends on the thickness of
the junction and the temperature.
AC Josephson Effect:When a dc voltage applied across the junction then ac
current of high frequency ( radio frequency) starts flowing across the junction.
When a static potential V0is applied across the junction. This results in
additional phase difference introduced by the cooper pair during tunneling
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can be
calculated using quantum mechanics.
Et

Where ‘E’ is the total energy of the system.
Here
E=(2e)V0 (since q=2e) since cooper pair contains 2electrons,
the factor 2 appear in the above eq.
Hence
2eV0 t
 

The tunneling current,
 
I  I 0 sin( 0   )
I  I 0 sin( 0 
2eV0 t
)

This is in the form
I  I 0 sin( 0  t )
Where  
2eV0

Or
2eV0
h
This represents an alternating current with angular frequency ‘  ’.
This is the a.c Josephson effect. This effect is utilized to generate
high frequencyr.f oscillations applying d.c voltage. A d.c voltage of
1microvolt generates a frequency of 483.6 MHz.

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1) When V0=0 there is a constant flow of d.c current iC across the
junction. This current is called ‘superconducting current’ and the
effect is the d.c Josephson effect.
2) So long V0< VC a constant d.c current iCflows.
3) When V0> VC , the junction has a finite resistance and the
2eV0
current oscillations with a frequency  
h
This effect is called the a.c Josephson effect.
Applications of Josephson’s Effect
1) Josephsoneffect is used to generate microwave with frequency  
2)
3)
2eV0
h
A.C Josephson effect is used to define standard volt.
A.C Josephson effect is also used to measure very low temperature
based on the variation of frequency of the emitted radiation with
temperature.
Importance And Characteristics of Josephson Junction
1)
A d.c flows across the junction in the absence of electric Or magnetic
field.
2)
When a d.c voltage is applied across a junction, a.c. is produced from
the junction(i.e, a.c Josephson effect)
e
3)
This a.c Josephson effect is used for the precise determination of  as
a voltage standard.
4)
5)
By virtue of a.c Josephson effect, the volt has replaced the ampere as
the fundamental unit of electromagnetism.
When a d.c magnetic field is applied across a super conducting
circuit, the maximum super current exhibits an interference pattern
as a function of intensity of magnetic field.
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SQUID
SQUID is an acronym for Superconducting Quantum Interference
Device. It is a magnetometer ie, it is a very sensitive device for
measuring even small changes in magnetic field. It is based on the
principle of Josephson effect.
SQUID consists of a Superconducting ring with two side arms P & Q
in opposite direction. X & Y are two very thin insulating junction (
Josephson Junction). Magnetic flux is applied in a direction
perpendicular to it.
Supercurrent flowing through the arm ‘P’ is branching in to two and
passing through the insulating junction X and Y. ( it is similar to the
splitting of light into the two coherent sources in Young’s Double slit
experiment) i.e, cooper pairs are tunneling through the junctions .
The supercurrents emerging from these junctions are combinig
together at Q .It is similar to the two splitted beam of light are allowed
to interfere with each other in Young’s double slit experiment. This
net supercurrent changes periodically with
the changein the
magnetic flux. The dependence of supercurrent with magnetic field is
similar to the interference pattern of light. Since the magnetic flux is
quantized the current changes in the discontinuousmanner.Even a
very small change in M.F of 10-21T can be detected accurately.
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Application of Squids
1. Squids are used as very sensitive magnetometer to measure
even a minute change in magnetic field in the order of10-21T
2. Used in the study of magnetic monopoles, gravitons etc.
3. Used to detect small disturbances in the earth’s magnetic
field. When a submarine or ship approaches a land, it
produces its own magnetic disturbances with earth’s field.
The squid identifies these minute changes of magnetic field
and hence detects the presence of ships, submarines, mines
etc.
4. Heart, brain etc. will generate very minute magnetic fields
in the order of 10-15 T. Squids have very high importance in
the measurement of such weak magnetic pulses and in their
pathological analysis.
5. Principle of squids is applied in MRI (Magnetic Resonance
Imaging) for the investigation and diagnosis of various
diseases.
APPLICATIONS OF SUPERCONDUCTIVITY
Invention of superconductivity has changed the modern world. Superconductivity has
developed new methods of energy production, energy saving, energy transmission
and energy storage. Superconductors are used to produce very strong magnetic
field. They are used as magnetic sensors to measure very feeble magnetic field,
27
as magnetic shields to provide field free space, as thermometers and detectors
etc. Some of the important applications in different fields are given below.
(a) Superconducting Magnets
Very powerful and persistent magnetic field can be produced with a
very low power. Conventional method requires a very large electrical power and
most of the energy is lost as Joule’s heat. But when superconductors are used,
the only power required is to keep them cool. Usually Type II superconductors
are used as the coils of the super conducting magnets. Here the external
changes in the magnetic field will not affect the magnetic flux and hence
persistent magnetic field can be established. They are smaller in size and less
expensive. This huge magnetic field has wide applications:
(i) To bend and to guide the charged particles in particle accelerators,
cyclotrons etc. Strong magnetic field is essential in large Physics machines like
colliders.
(ii) For controlling and focusing of high temperature plasma for the controlled
nuclear reactions.
(iii) Used in MAGLEV: (magnetic levitation). The repulsion between the
magnetic field in a solenoid and a nearby super conducting track is used to
raise (levitate) maglev coaches a few centimeters above the track. Such a train
with these coaches can easily fly over the tracks without touching on it and
without any friction with more than 500 km/h. This principle is applied in the
ship-drive system. The magnetic expulsion of super conductors is also used for
the magnetic propulsion of satellites in to the orbits from the ground stations.
(iv) Super conducting magnets are used for the manufacturing of efficient ore
separating machines.
(b) Medical Field
(i) MRI: One of the most important applications of super conductors is MRI
(Magnetic resonance imaging) for medical diagnosis. When a strong and steady
magnetic field from a cylindrical super conducting magnet is applied across the
body of the patient, nuclei of hydrogen atoms of the body align along the field
direction. When an electromagnetic pulse is applied they realign and emit their
own characteristic signals. Analysing these signals, diagnosis can be made
easier and safer. MRI is more reliable and free from harmful effects of other
radiations like X-rays.
28
(ii)M.E.G (Magneto Encephalography): A group of squids is used for the
treatment of epilepsy and the technique for this is called MEG. Sensing the
electric and magnetic pulses produced from the different parts of the brain the
epileptic centre can be exactly identified.
(iii) Superconducting susceptometer: It is a squid working with a super
conducting magnet and it is used to detect the iron content in the body.
(iv) Squids are used to measure very minute magnetic fields produced from
heart and brain accurately and used for pathological analysis of their
functions.
(v) Super conducting magnetic field is used to remove tumour cells from the
healthy cells using high gradient magnetic separation method.
(c) Electric Motors and Generators
Another important application of super conductors is the
manufacture of rotating electrical appliances like electric motors, generators
etc with super conducting windings. Since ferromagnetic iron core is not used,
eddy current loss, hysteresis loss etc are avoided completely. Hence size,
weight and cost have been reduced considerably. These machines are smaller,
more efficient and more easily portable and they provide higher output.
(d) Power Transmission
It is estimated that more than 20 % of electrical energy is
wasted as
loss during transmission with ordinary cables and wires. But if
super conducting cables are used for power transmission, such energy loss can
be minimized to a great extent. Scientists are actively engaged in developing
new super conducting materials which will operate even at higher temperature.
Transformers with super conducting windings are free from hysteresis and
power losses. High temperature super conducting cables are used for
underground power transmission effectively and efficiently in a more economic
manner.
12 R
(e) Electronics and Devices
(i)Squid: Squid is very small sensitive device based on Josephson Effect. It can
be used as a magnetometer to measure very feeble magnetic fields. Hence it is
29
used for diagnosis of certain diseases, and for detection of mines and
submarines. Squid is used to explore the oil and mineral deposits in earth, to
separate ores and to study about the magnetic monopoles and gravitons.
(ii) Josephson Devices: Based on Josephson principle so many sensitive devices
have been fabricated. Millimeter detectors, parametric amplifier, mixer, super
conductor fuses and breakers, super conducting voltage standards,
magnetically controlled super conducting switches etc. are some of the
important devices. Super conductors are used as bolometers to detect different
types of electromagnetic radiations like infrared radiations.
(iii) Meissner Effect: There are certain devices working on the basis of Meissner
effect. A super conducting cylinder and a disc can be used as a magnetic
bearing. Meissner effect is utilized in the fabrication of different kinds of
bearings which will operate without any friction in many rotating machineries.
(f) Computers and Information Processing
If super conducting wires are used, a large number of
components and circuits can be set up in a smaller area. Hence this reduces
size and shape of the devices. Such computers will function with very high
accuracy without any Joule’s heat. So super computers are fabricated with
superconducting materials. A Josephson junction increases the speed of super
computers because such logic elements can be operated at a speed of Pico
seconds.
***********************************
Reference
1.
2.
3.
4.
5.
6.
7.
Engineering Physics : A. Marikani
Engineering Physics :Randehir Singh
Engineering Physics: K. Rajagopal
Engineering Physics: TessyIssac
Engineering Physics: Jacob Philip
Engineering Physics: S. Gopinath
A text book of Engineering Physics: M.N Avaghanulu
30
MODULE-II
CHAPTER-1
NANOTECHNOLOGY
Introduction
“Nanoscience is defined as branch of Physics dealing with study of
special phenomena that occur when objects are of size between 1nm to
100 nm in at least one dimension.”
Thenanoscience and nanotechnology primarily deal with
synthesis,characterization, exploration and exploitation of nanostructured
materials. The individual nanostructure include clusters, quantum dots,
nanocrystals,nanowire and nanotubes. The collection of nanostructures involve
arrays, assemblies and superlattices of the individual nanostructures.
 Zero dimension – Nanosized particles are generallyclassified in this
group( Nano particle).
 One dimension- Here at least one out of three dimensions is in
nanometers. Layers, thin filims, surface coatings in nanoscale are
classified in this group.
 Two dimension – In this classification any two dimensions are
measured in nano scale. Nanowires, Nanotubes, nanorods etc.
belonging to this group.
 Three Dimension- Equiaxednonometer sized grains are included in
this group. Examples are Quantum dots, Fullerenes, Dendrimers etc.
The value of 1nm= 10-9m ( billionth of a meter) when the particle size gets
reduced, most of the physical properties of the nanomaterials get changed. For
eg. Bulk silver non toxic where as Silver nanoparticle are capable of killing
viruses upon contact. Properties like electrical conductivity, colour , strength,
31
weight…. Change when the nanolevel is reached . Opaque substance becomes
transparent eg. Copper
Why the properties of nanoparticles are different?
Two principle factors causing the properties of nanomaterials to differ
significantly from other materials.
1) Increased surface area to volume ratio
Let us consider a sphere of radius ‘r’
Its Surface area = 4Πr2
4
3
Its Volume = r 3
Surface area to Volume Ratio =
3
r
[
4r
3

4 3
r
r
3
2
Since
]
Thus when the radiusof the sphere decreases its surface area to volume ratio
increases. When the particle size decreases, a greater proportion of atoms are
found at the surface compared with larger particles.It makes material more
chemically reactive.
2) Quantum Confinement Effects
Quantum confinement is responsible for the increase of energy difference between
energy states and bandgap. When atoms are isolated, energy levels are discrete.
The quantum confinement effect can be observed once the diameter of the particle
is of the same magnitude as the wavelength of the electron wave function. When
material substantially from those of bulk materials.
In bulk materials the energy states are continuous and the dimension is
large compared to the wavelength of the particle. However as the confining
dimension decreases and reaches a certain limit, typically in nanoscale, the
energy spectrum turns to discrete. As a result, the band gap becomes size
dependent.
ie, ∆Enano> ∆Ebulk
32
SYNTHESIS AND ANALYSIS OF NANOMATERIALS
The nanomaterials are synthesized using a number of methods.
These methods are generally classified into two categories: 1) Top – down process
and 2) Bottom – up process
1) Top – down process
To synthesize a nanomaterial, if a bulk material is used as a starting
material then the method is known as top-down process. In this method, a bulk
material is crushed into fine particles using the process like mechanical alloying,
laser ablation, sputtering, etc...The examples of the top-down process are :
1. Ball milling
2. Laser ablation
3. Sputtering
4. Arc plasma
5. Electron beam evaporation
6. Photolithography
Advantages
1. It is the common technique used for the fabrication of semiconductor devices.
2. Large wafers can be used to fabricate nanomaterials.
3. Material selection is wide.
33
Disadvantages
1. Perfection of materials is poor and final product may contain impurities and
disorders.
2. Large wastage of materials.
3. The limit of resolution of the instruments used for the synthesis of materials is a
great problem.
4. Construction of clean rooms for the preparation of nanomaterials is a tedious
process.
5. Cost of equipments is very high.
6. With small physical areas heat dissipation is very high.
Uses
1. Used in the fabrication of electronic components.
2. Quantum wells and high quality optical mirrors are fabricated with this technique.
2) Bottom – up Process
In this method, the nanomaterials are prepared by arranging atom by atom.
Due to the nucleation and growth, bigger size grains or a cluster of atoms having a
size less than 100nm are produced. These methods produce the nanomaterials due
to some chemical reactions and hence these methods are called chemical methods.
The examples of the bottom-up process are:
1. Chemical vapour deposition
2. Sol-gel method
3. Electro deposition
Advantages
1. It is more economical than top-down because there is no material loss due to
etching.
2. Covalent bonds between the atoms are strong. Hence the stability is very high.
34
Disadvantages
This method requires high control on the process through which nanomaterials
are produced
Classification Or Different Type of Nanostructures
The materials which have atleast one dimension in the order of nanometer are
called nanostructured materials. Based on the shape and size, the nanostructures
are classified in to four groups as:
 Zero dimension – Nanosized particles are generallyclassified in this
group ( Nano particle).
 One dimension- Here at least one out of three dimensions is in
nanometers. Layers, thin filims, surface coatings in nanoscale are
classified in this group.
 Two dimension – In this classification any two dimensions are
measured in nano scale. Nanowires, Nanotubes, nanorods etc.
belonging to this group.
 Three Dimension- Equiaxednonometer sized grains are included in
this group. Examples are Quantum dots, Fullerenes, Dendrimers etc.
NANOSTRUCTURES
A Nanostructure is an object whose size is intermediate between size of
an atom (0.1nm) and size of a microscopic (1µm sized) object. Various types of
nanostructure are nanoring, nanoshell, quantum dots etc.
(a)Nanoring:Ananoring is a ringformed crystal. Nanorings are made up of fine
nanobelts they are rolled up as coils layer by layer with as many as hundred
loops.
35
The diameter of a nanoring lies usally in the range 1-4 µm and thickness in the
range 10-30nm. The first nanoring made was zinc oxide nanoring.
Preparation
A nanoring can be made by solid vapour techniquefrom the powders of
ZnO, Indium oxide ,lithium carbonate in a horizontal tube furnace. The
material is heated to 14000C in argon and it get deposited on a Silicon
substrate. Around 20-40 % of the deposited material contains nanoring.
Applications
1. Nonarings of ZnO can be used for fabricating piezoelectric based fluid
pumps and switches for biotechnology.
2. It can be used as a memory storage device.
3. Used as sensors, resonators and transducers for nanoelectronics&
biotechnological applications.
4. It is used for studying piezoelectric effect at nanoscale.
b)Nonoroads
“ Nanoroads are nanostructures having two spatial dimension in the
nanoscale range”. These can be made from metals Or Semiconductors.
Their length is 3-5 times their width.
36
Aggregated Diamond Nanoroads (ADNRS) are a nanocrystals
from of diamond.
Preparation
Nanoroad are produced by direct Chemical Synthesis.A combination of
ligands act as a shape control agents & bond to different facents of the
nanorod with different strengths. Due to this, different faces of nanorods
grow at different rates, producing an elongated object.
Applications
1. These are used in display technologies. By changing the orientation of
nanorods with applied external electric field, the reflectivity of rod can
be altered, resulting in superior displays.
2. The picture elements are known as pixels are composed of sharp tipped
objects of nanoscale dimensions. These can improve picture quality of a
television.
3. Thin film computers are nanorod based.
4. Gold nanorods are useful materials for sensing and imaging.
5. Gold nanorod find applications in optics including polarizers, filters &
to improve the storage density in compact diaks.
C) NANOSHELL
“Nanoshell is a type of spherical nanoparticle consisting of a dielectric core
which is covered with a thin metallic layers”. This type of nanoparticle is also
referred as core-shell particle.
In nanoshells electrons oscillate
simultaneously with respect to all the ions and this oscillation state act as a
quasiparticle called Plasmons.The inner shell (electric core) & the outer shell
37
of the nanoshell hybridize to give a lower Or higher energy state.The lower
energy state couples strongly with incident light while higher energy state
couples weakly to incident light. The extent of hybridization b/w inner &
outer shell of nanoshell depends on the thickness of outer shell layer. Strong
hybridization takes place when outer shell has small thickness and vice versa.
Nano shaped materials with only shell and devoid of core are called
nanobubbles or nanocapsules.
Preparation
Nanoshell are synthesized by multistep process. Firstly a suspension of
nanoparticles in a solution is obtained. Then a small sized seed colloid is
attached onto dielectric nanoparticles thus forming a discontinuous shell. At
least a continuous shell is grown up by using a chemical reduction of metal
attached to dielectric nanoparticles.
Properties of Nanoshells
1. The size of nanoshells are controlled by the radiations that interacts with it
2. They are immune to photo bleaching and shows enhanced luminescence
3. They have spectral tenability and absorption/scattering tenability.
Applications Or Uses
38
1. Nanoshells are used for cancer treatment. Goldnanoshells are inserted into the
cancer tumour and then radiation are made to incident on these nanoshells.
Nanoshells absorbs these radiations and their temperature increases to above
30 0C. The high temperature causes death of tumour cell.
2. Nanoshells are used for biomedical imaging. This technique provides better
resolution for identifying tumors. Nanoshells injected into the blood stream
accumulate at the tumor sites. These particles glow when subjected to low
intensity radiation, which allows tumor areas to be visible through the
technique ‘optical coherence tomography’.
3. They are used for the therapeutic application.
4. Silica nanoshells are used for the encapsulation of drugs.
5. Titaniananoshells are used for sensing purpose.
6. The Zirconia nanomaterials can be a potential candidate as a catalyst in fuel
cells
d) Nanoparticle
“ A nanoparticle is defined as a small object having all three special
dimensions in nanometer scale and behaves as a single unit in terms of its
transport and other properties”. Quantum dot is an example of
nanoparticle.
These are further classified into 2-categories( Based on dimension)
1) Ultra fine particle (UFP) : They are nanoparticle having size b/w
1nm-100nm.
2) Fine particle :fine particle having dimension in the range 100nm to
250nm.
Nanoparticles have great scientific interest as these act as
bridge between bulk materials & atomic/molecular structures. The
physical properties of a bulk material is constant and independent of size,
but at nanoscale range the physical preoperties become size dependent.
For eg.Bulk gold is yellow in colour while nanoparticle of gold have red
colour. Similarlybulk silicon is of grey colour but at nanoscale, its
colour is red. The melting point of bulk gold is 10640C but that of
nanoscale gold is ≈ 3000C.Nanoparticles are present as an aerosol (mostly
solid or liquid phase in air), a suspension (mostly solid in liquids) or an
emulsion (two liquid phases).
39
Preparation
Nanoparticles can be synthesized by several methods. Solid powder of material
is heated upto 10,000K using thermal plasma. This results in evaporation of
solid powder. When these vapours are exiting the plasma region then these cool
down as nanoparticles.
USES
1.
Quantum dots are used for making semiconductor lasers and high
speed switching devices.
2.
These can be used in memory storage device
3.
Biotechnology
4.
Medical instrumentation.
5.
Coolants having suspended nanoparticles work well in transferring
heat for heat engines.
6.
It is an important ingredient of many nano applications.
7.
It can be use as sensor.
Properties of Nanoparticles
The properties of substance are usually measured by taking large sample
volume (~ 1023 atoms/ Molecule). However when these properties were
checked for same material at nanoscale level then large difference were
observed in many physical properties. This means at nanoscale level,
physical properties becomes size dependent. Some of the physical
properties of nanoparticles are discussed below.
a) Physical Properties
1. Melting point
40
The melting point of gold in bulk form is around 1300K. The
melting temperatute significantly decreases upto around
700K,when the particle size is decreased around 10 to 20 nm. The
variation of the melting temperature of gold with particle size is
shown in fig. The melting temperature of CdS is slightly higher
than 1700K in the bulk form. The melting point of CdS reduces to
600K, When its partice size is around 10 to 15 nm.
2. Interatomic distance
The interatomic size get reduced when there is a reduction in
particle size is around 10 to 15nm.
b)
Optical Properties
In the case of metallic nanoparticles, the optical properties are
closely related to surface Plasmons. Plasmons is basically a quantum of
plasma oscillations. These plasmons are analogue of photons Or phonons,
which are quantum of light and sound waves respectively. The plasmons
which are concentrated at the surface of materials are reffered as surface
Plasmons and they can be used to give colour to the materials. When
nanoparticles are exposed to light of wavelength comparable to the
wavelength of plasmons, the plasmons start interacting with these
radiations. The properties of surface plasmons are controlled by the shape
of surface, which hold these plasmons. The surface plasmons control the
light that couples with it and thus nanoparticles exhibit different colours.
Thus size of the particle is responsible for the amazing colours of
nanomaterials.
ie, optical properties like colour, transparency are observed to change at
nanoscale level.
For eg.Bulk gold is yellow in colour while nanoparticle of gold have red
colour. Similarlybulk silicon is of grey colour but at nanoscale, its colour
is red. Another eg.is of ZnO, which at bulk scale blocks ultraviolet light
and scatters visible light and give white appearance. While
nanosizedZnOis very small in particle size compared with wavelength of
visible light and it does not scatter it. Thus it appears transparent.
41
The main reason for changing optical properties at nanoscale level is that
nanoparticles are so small that electronsin them are not as much free to
move as in the case of bulk material . Because of this restricted movement
of electrons, nanoparticles react differently with light as compared to bulk
material.
c) Magnetic Properties
 Non magnetic material became magnetic when cluster size reduces to
80 atoms.
 Bulk magnetic moment increases with decrease in co-ordination
number. Smaller particles are more magnetic than the bulk material.
 Ferromagnetic materials exhibit Super ferromagnetism at nanograin
size.
 Paramagnetic material exhibit ferromagnetism at nano grain sizes.
The strength of a magnet is measured in terms of coercivity and
saturation magnetization value. These values increase with a decrease with
a decrease in grain size and an increase in the specific surface area of the
grains.
Magnetism in bulk and in nanoparticle
Meta
Bulk
Cluster
l
( Nanoparticle)
Na,K
Paramagnetic
Ferromagnetic
Fe ,
Ferromagneti
Superparamagneti
Co,
c
c
Ni
Rh
Paramagnetic
Ferromagnetic
d) Mechanical Properties
1) The hardness of a nanomaterial increases with the reduction in particle
size. Eg. The hardness of copper gets increases two times when its particle
size is 50nm and 5times harder than bulk material at 6nm grain size.
2) At nanoscale level if size of the object is changed then percentage
change in number of atoms on the surface is very large. Due to this
melting point starts depending on the size of object and goes on
decreasing with decrease in size.
42
Eg.The melting point of bulk gold is 10640C but that of nanoscale gold is ≈
3000C
3) Young’s Modulus of nanomaterials decrease with decrease in size.
4) The nanomaterial are quite brittle and shows reduced ductility under
tension.
5) The nanomaterials are called super plastic materials because they have
extensive tensile deformation without cracking Or fracture.
e) Electrical Properties
1) In the case of metals electronic properties are mainly determined by
electronic mean free path which is usually of the order of 10nm. When
the materials are transformed to a state of nanomaterials, the overall size
of the conductor may be equal to or less than the mean free path. At this
stage electrons are confined at the surface, which increases the
resistivity of nanoparticles.
2) The electrical conductivity decreases with reduced dimensions due
to increased surface scattering. Eg.Carbon nanotubes can be conducting
Or semiconducting in bahaviour while bulk carbon ( graphite) is a good
conductor of electricity.
3) Due to the size confinementthe capacitance decreases. 4) The
current voltage (V - I) characteristic of a nanoparticle is a staircase.
This phenomenon is called coulomb blockade effect and.
5) The dielectric constants of nanomaterials are also very high due to
the large number of grain boundaries.
f) Quantum Confinement Effect Quantum confinement is responsible
for the increase of energy difference between energy states and band gap.
When atoms are isolated, energy levels are discrete. The quantum
confinement effect can be observed once the diameter of the particle is of
the same magnitude as the wavelength of the electron wave function.
When material substantially from those of bulk materials.
43
In bulk materials the energy states are continuous and the dimension is
large compared to the wavelength of the particle. However as the confining
dimension decreases and reaches a certain limit, typically in nanoscale, the
energy spectrum turns to discrete. As a result, the band gap becomes size
dependent.
ie, ∆Enano> ∆Ebulk
Electrical
Increased electrical conductivity in ceramics and magnetic
nanocomposites , increased electric resistance in metals
Increased magnetic coercivity up to a critical grain size ,
super paramagnetic behaviour
Improved hardness and toughness of metals and alloys,
Mechanical
ductility and super plasticity of ceramic
Spectral shift of optical absorbtion and fluorescence
Optical
properties, increased quantum efficiency of semiconductor
crystals
Magnetic
CLASSIFICATION OF NANOMATERIALS
The organic materials come under two categories, Organic & inorganic.
Well known nanomaterials like Fullerene( C60) and Carbon nanotubes (CNT) come
under the category of organic nanomaterials. Biomaterials like deoxyrobonuclic
acid ( DNA) and proteins come under the category of inorganic. But the
requirement of fast growing world cannot meet with these nanomaterials. So new
classes of the materials are introduced known as nano composites. Materials
derived by the combination of two or more building blocks, containing atleast one
component in the nanomaterscale, are reffered as nanocomposite materials.
i.e ,Nanomaterials are normally classified into four types:
a)
b)
c)
d)
Carbon based nanomaterials
Metal based nanomaterials
Dendrimers
Nanocomposites.
a) Carbon based nanomaterials: These nanomaterials are mostly
composed of carbon having the usual shapes like spherical, ellipsoidal Or
44
tubes. Spherical Or ellipsoidal carbon nano materials are called Fullerene
while cylindrical shaped nanomaterials are called carbon
nanotubes(CNT).
b) Metal basednanomaterials: These nanomaterials include quantum dots,
nanogold, nanosilver and metal oxide such as titanium oxide.
c) Dendrimers :These nanomaterial are nanosized polymers built from
branched units.The surface of dendrimers has numerous chain ends,
which can be tailored to perform specific chemical functions. This
property could also be useful for catalysis.Also because three
dimensionldendrimers contain cavities into which other molecule could
be placed, these are thus useful for drug delivery.
d) Nanocomposites: Materials derived by the combination of two or more
building blocks, containing atleast one component in the nanomaterscale,
are reffered as nanocomposite materials. Or properties.Nanocomposite is
a multiphase solid material in which one type of nanoparticles are
combined with other type of nanoparticles Or nanoparticles are combined
with other large bulk type materials. Nanocomposites such as nanosized
clays are already being added to products ranging from autroparts to
packing materials, to enhance mechanical, thermal and flame retardant.
(a) Fullerene (C60)
Fullerene was discovered by H. Kroto, R Curl, and R. Smalley in 1985.
Fullerene is basically an allotrope (Different forms) of carbon like Graphite or
Diamond. It consists of 60 carbon atoms, each of mass 12 arranged in the
shape of a soccer ball (foot ball).. It has 12 pentagonal and 20 hexagonal faces
symmetncally arranged to form a molecule .This structure was proposed by
Richard Buckminister fuller. Spherical fullerenes are also known as bucky ball.
The molecular separation is 1 nm and the molecules are held together by weak van
der Wall’s force. Its density is 1.65 g/cm3. Its appearance in black and it is
odourless. Fullerenes are highly hydrophobic in nature. The band gap is of the
order 1.6 eV.They are highly photorefractive in nature. It is soluble in common
solvents like benzene & toluene.
45
Preparation
Fullerenes are in fact produced in small amounts naturally from fire or
lightning.
In laboratory, fullerenes are produced by sending a large current through two
nearby graphite electrodes kept in an atmosphere of helium. The evaporated
graphite takes the form of soot, which is dissolved in a nonpolar solvent. The
solvent is dried away and the fullerenes can be separated from the residue. Now
fullerenes are prepared from thepyrolisis of various hydrocarbons.
Uses
1) C60 fullerenes are useful for secural biological applications because these are
non toxic to cells.
2) It is a powerful antioxidant and react readily with free radicals which are
usually responsible for death or damage of a cell.
3) Major pharmaceutical companies exploring the use of fullerenein controlling
neurological damage of diseases such as Alzhemerisdesease which result
due to radical damage.
4) C60 fullerene can be used as organic photovoltaic cell.
5) Fullerene are chemically reactive & can be added to polymer structures to
create new co-polymers with specific physical & mechanical properties.
6) These can be also used to make a nanocomposite.
Carbon Nanotubes (CNT)
One of the most useful nanomaterials is the carbon nanotubes.
Nanotubes are members of the fullerene structural family, which also
includes the spherical bucky balls. It is considered as a stretched form of
buckyballs, a sheet of carbon curved into a cylinder capped at each end.
46
In 1991 Japanese scintistSumioIijima discovered a multiwalled carbon
nanotubes & in 1993, he discovered single walled carbon
nanotubes.Their name is derived from their size, since the diameter of a
nanotube is on the order of a few nanometer, while they can be up to
18c.m in their length.
“ Carbon nanotubes are defined as allotropes of carbon having
cylindrical nanostructure”.These are also known as bucky tubes.
Nanotubes have been constructed with length to diameter ratio up to
132,000,000 : 1, which is significantly larger than any other material. These
cylindrical Carbon molecules have novel properties that makes them
potentially useful in many applications in nanotechnology, electronics,
optics and other field of material science as well as potential uses in
architectuaral fields. They exhibit extraordinary strength & unique
electrical properties & are efficient thermal conductors.
Types of CNT
There are two types of Carbon nanotubes
1. Single Walled CNT (SWNT)
2. Multiwalled Carbon Nanotubes (MWNT)
1. Single Walled CNT (SWNT)
This type of nanotubes can be formed by rolling Graphene
sheet. Graphene is a single planar sheet of carbon atoms that are
densely packed in a honeycomb crystal lattice. Single walled
nanotubes consists of onlyone layer.These are further classified as
47
:Zigzag, Armchair, and Chiral. The diameter of a SWNT varies
varies from 1 to 5nm, with a tube length that can be many millions
of times longer. SWNT’s are an important variety of carbon
nanotubes because they exhibit interesting electric properties.
Their bang gap varies between zero to about 2eV and their
electrical conductivity can show metallic Or semiconducting
behavior , where as MWNTs are zero-gap metals. SWNTs can
be excellent conductors . SWNT is more stable. SWNT has
better define shape of cylinder than MWNT. MWNTs has
possibilities of structure defects & its nanostructure is less
stable.
2)Multiwalled Carbon nanotubes (MWNT)
Multi-walled nanotubes (MWNT) consists of multiple rolled layers ( Concentric
tubes ) of graphite. ie, MWNTs comprise an array of nanotubes that are
48
concentrically nested-like rings of a tree trunk. The inner diameter of a MWNT
varies from 1.5nm to 5nm & its outer diameter varies from 2.5 to 30nm.
There are two models which can be used to describe the structures
ofmultiwalled nanotubes.
1. Russian doll model
2. Purchment model
1. Russian Doll model : In this model sheets of graphite are arranged in
concentric cylinder.eg. aSWNT within a larger single walled nanotubes.
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2. Parchment model: In this model a single sheet of graphite is rolled in
around itself , resembling a scroll of parchment Or a rolled newspaper.
Preparation
Arc discharge: Two graphite rods are kept with a separation of 1mm and they
connected to a dc, 15 to 25 V.By applying a high current in the order of 50 to 120
A, carbon vaporizes and produces plasma.30 to 90% is CNT. Short tubes with
diameter 0.6nm to 1.4nm is called SWCNT and short tubes with inner diameter 13nm and outer diameter of approximately 10nm is called MWCNT.
Properties Of Carbon Nanotubes
1. Strength
 Carbon nanotubes are the strongest and stiffest material yet
discovered in terms of tensile strength and elastic modulus. A
SWNT can be up to 100 times stronger than that of steel with the
same weight.
 The young’s modulus of SWNT is up to 1TPa, which is 5 times
greater than steel (230 GPa).
 The density of nanotubes is only 1.3 g cm-3. That means that the
material made up of nanotubes are lighter and more durable.
 Nanotubes also have very high aspect ratio.
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 The length of nanotube is usually around 1mm, while the
diameter for SWNT is only 1nm ( 50nm for MWNT). This property
makes nanoyubes useful foe tops and nanowires.
2. Thermal

The thermal conductivity of nanotubes (1200 to 3000W m-1 K-1)
is nearly five times greater than that of copper (4003000W m-1 K-1).

Superconductivity has also been observed only at low
temperature with TC ~0.55 K for 1.4nm diameter SWNT and ~ 5 K for
0.5nm diameter.
3. Electrical Property

CNT has distinct electrical property. One of the important
properties of CNT is that it can exhibit the characteristics of a metal Or
semiconductors.

Armchair structure CNT has a metallic bahaviour whereas the
chiral structure has semiconducting behaviour.
Nanocomosites
Materials derived by the combination of two or more building blocks,
containing atleast one component in the nanomaterscale, are reffered as
nanocompositematerials.i.eA composite is a combination of two Or more
different materials mixed in such a way so as to produce the best
properties of both. Composite behaviour results from some combination
of the properties of individual.
They classified into three categories
1. Ceramic Matrix Nanocomposite
2. Metallic Nanocomposite
3. Polymer Or Polymeric nanocomposite
1. Ceramic Matrix Nanocomposite : These are the composite that contain
ceramic nanophases either comprising overall half of the total volume fraction
Or with an interconnective relationship.
Properties
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 These composite exhibit great improvement in mechanical properties
such as strength, toughness and hardness.
 They have enhanced ductility, toughness and superplasticity.
 Due to disordered grain boundary interface, the electrical and magnetc
properties are greatly changed with bulk material.
2. Metallic Nanocomposites : “It is a kind of composite obtained by
combining metal oxides and nanoscalealuminium powder in a Silica base.”
Commonly used metallic nanocomposites are Metal/Metal nanocomposites and
Metal/Ceramic nanocomposites.
Examples of metallic nanocomposites are Al2O3/W, Mo, Ni, Cu, Co, Fe;
ZrO2/Ni, Mo; MgO/Fe, Co, Ni.
These have improved properties compared with other nanocomposites
Properties
1. Increasing hardness, strength and super plasticity
2. Lower melting point
3. Enhanced conductivity due to reduced grain size
4. Increased electrical resistivity due to increased disordered grain surfaces.
4. Improved magnetic properties such as magnetic coercivity,
superparamagnetisation and saturation magnetization.
These materials are used in making power transformers, magnetic
recording heads and microwave applications.
(ii) Polymeric Nanocomposites: “These are polymer matrices reinforced with
nanoscale fillers”The polymeric product consists of two or more phases each in
the nanometer range, generally referred as polymeric nanocomposites. Polymeric
nanocomposites were developed in the later 1980s for both commercial and
academic purpose. Their matrices may be epoxies, polypropylene, polyesters and
other plastics. Structural, mechanical, thermal and flame retardant properties are
considerably improved in these materials in comparison with the conventional
materials. Different nanocomposites are available based on polymers such as
clay/poIymer, carbon nànotube/polymer and metal/polymer.
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Properties
I. Efficient reinforcement of mechanical properties with minimum loss of
elongation and flexibility
2. They are light weight
3. Improved thermal stability and flame resistance properties
4. Excellent chemical and weather resistant properties
5. Improved biodegradability for biodegradable polymers
6. Improved electrical properties for conducting polymers.
7. These have increased absorption for ultraviolet wavelengths.
Uses:
1. It is used in barrier packages, food packages, fire retardant pouches, high speed
printing film , gasoline tanks, fuel line tubes and shock absorbers.
2. Commercial nylon – clay hybrid with 2% clay can be used as a gas and UV
barrier as well as for high heat resistance.
3. These are also used in sensing devices.
4. It is also used as light emitting diodes.
Uses OfNanomaterials Or Applications
1. Nanoparticles are ceramic based coatings that make a paint lot more
durable and resistant to rock chips and scratches. In addition to holding
up better to wrathering, nanoparticles have richer and brighter colours
than traditional pigments.
2. Scientists have announced that they have invented nanotech based
coatingmaterial that act as a permanent air purifier. In near future such
paint will be gradually used on buildings to improve air quality. The core of
such paint is titanium oxide based compound developed using advanced
nanotechnology. Exposed under sunlight, the substance can automatically
decompose ingradients like formaldehyde that causes air pollution.
3. Nanotechnology is being used to produce a photovoltaic material, that can
be spread like a plastic wrap Or paint.
4. Nanodevices are used for data storage.
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5. Using nanotechnology it will be possible in near future to grow cardiac
muscle tissue artificially. This will allow as to repair and restore a damaged
human heart.
6. If we could cover the proteins that exist on influenza virus, then we could
prevent the virus from recognizing and binding to our body cells. A
protein recognition system has already been developed, thus nanotechnology
can help from protecting individuals from viral diseases.
7. Next generation computer chips.
8. Automobiles with greater fuel efficiency
9. Better weapons: Gun powder, electromagnetic launcher gun.
10. Large electro chromic display devices : Displays information by changing
colours when a voltage is applied.
11. High definition TV : The use of nanophosphors render very high resolution
Low coast flat panel displays.
12.Tougher and harder cutting tools: Cutting tools made up of
nanocrystallinemateriaols such as tungsten carbide, tantalum carbide are
much harder, much more wear resistant and last longer than their
conventional counter part.
13.Elimination of pollutants : Due to their enhanced chemical activity,
nanomaterials can be used as catalysts to react with toxic gases such as
carbon monoxide and nitrogen.
14.High energy density batteries : Less frequent recharging, last much longer.
15.Blocking of UV rays: Nano-Zinc oxide Ornanotitania is used in many
sunscreen to block harmful UV rays.
16.Electrical devices : BaTiO3nano powders are used to prepare ceramic
capacitors. It has reduced size and enhanced capacitances.
APPLICATIONS OF NANOTECHNOLOGY
The field nanotechnology revolutionalises almost all fields of
Science and Technology. The various applications which already have been
introduced or in a process of development are listed below. All these different
applications are grouped into six and some of the most important applications from
each category are listed below.
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(a) Electronics and Computing
(b) Power/Energy
(c) Engineering
(d) Health and Medical
(e) Environment
(f) Consumer goals.
(a) Electronics and Computing
The electronic application of nanotechnology includes:
1. Fabricating transistors from carbon nanomaterials. This enables the
minimisation of transistor dimensions of the order of few nanometers and
developing techniques to manufacture integrated circuits built with nanotube
transistors. Developing molecular-sized transistors may allow us to shrink the
width of transistor gates to approximately one nm, which will significantly
increase transistor density in integrated circuits.
2. Electrodes made from nanowires enable flat panel displays to be flexible as
well as thinner than current flat panel displays.
3. Transistors built in single atom thick graphene film enables to achieve very
high speed.
4. Research for new generation transistors which is a combination of gold
nanoparticles with organic molecules- NOMFET (Nanoparticle Organic
Memory Field-Effect Transistor) is going on.
5. Nanosized magnetic rings are used to make Magneto resistive Random
Access Memory (MRAM) with a memory density of 400GB per square
inch.
6. Carbon nanotubes can be used to fabricate a flat panel display, which offers
high resolution and high tenability.
7. Quantum dots are nanoscaled objects, which can be used for the construction
of lasers. The advantage of a quantum - dot laser over traditional
semiconductor laser is that their emitted wavelength depends on the
diameter of the dot. Quantum dot lasers are cheaper and offer a higher beam
quality than conventional laser diodes.
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8. Silicon surface depositing small amount of gold on it (looks like CD having
nm dimensions ) has storage density million times higher than conventional
storage devices.
9. CNTs are used in nanoelectronics, batteries , displays and for the
manufacturing low cost solar panels.
(b) Power/Energy
1. The main advantage of nanosystems is that the energy consumption is very
low in these systems.
2. Nanobatteries are the most prominent member included in the family of
nanodevices. Conventional Lithium ion batteries have the size of the order of
micrometer; whereas the size of nanobattery is of the order of nanometers. By
using nanostructured anodes and cathodes, better recharging time, which is 80
times more than the conventional batteries could be achieved.
3. Another application of nanomaterials is in the construction of supercapacitors.
The capacitors allow storage of large amount of energy and can be recharged
quickly. Nanomaterials boost the possibilities of supercapacitors with the
discovery of novel nanomaterials.
4. The efficiency of Silicon based solar cells are of the order of 25%, where as
the most efficient solar cells of the present days is of 35%. It is predicted that
Quantum dots can provide high efficient solar cells with an efficiency of 85%.
5. Nanotechnology can be used in hydrogen based fuel cells, which can offer
solutions to material costs, fuel cell efficiency and storage of hydrogen.
6. “Nanofluids” such as engine oils contains copper like nanoparticles has 40%
increase in thermal conductivity.
(c)Engineering
Engineering applications of nanotechnology includes:
1. The synthesis of new materials, which are more stable and heat resistant than
conventional materials.
2. The major application of nanomaterial is in the field of space research.
Carbon nanotubes are used to make the cables needed for the space elevator,
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3.
4.
5.
6.
a system which could significantly reduce the cost of sending materials into
the orbit.
Carbon nanotubes are used to reduce the weight of spaceships by increasing
the structural strength.
The MEMS made with nanoparticles are used for the production of thrusters
for spacecraft. This reduces the weight and complexity of thruster systems
used for interplanetary missions. One cost-saving feature of these types of
thrusters is their ability to draw more or less MEMS devices depending upon
the size and thrust requirement of the spacecraft.
Carbon nanotubes are used to build lightweight solar cells. These solar cells
are capable of replacing fuels in spacecraft thereby solving the problem of
lifting high.
The nanosensors are used to monitor the levels of trace chemicals in
spacecraft to control the performance of life support systems.
(d) Health and Medicine
1. One application of nanotechnology in medicine is to deliver drugs, heat,
light or other substances to specific types of cells (such as cancer cells).
Particles are engineered so that they are attracted to diseased cells, which
allow direct treatment of those cells. The drug is encapsulated in a
nanoparticle which helps it pass through the stomach to deliver the drug into
the bloodstream. This technique reduces damage to healthy cells in the body
and allows earlier detection of disease.
2. Nanoshells concentrate the heat from infrared light to destroy cancer cells
with minimal damage to surrounding healthy cells. Nanoparticles, when
activated with x-rays, generate electrons that cause the destruction of cancer
cells. This is intended to be used in place of radiation therapy with much
less damage to healthy tissues.
3. Quantum Dots (qdots) may be used in the future for locating cancer tumors
in patients and in the—near term for performing diagnostic tests in samples.
4. Iron oxide nanoparticles can be used to improve MRI images of cancer
tumors. The nanoparticle is coated with a peptide that binds to a cancer
tumor. Once the nanoparticles are attached to the tumor the magnetic
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5.
6.
7.
8.
9.
property of the iron oxide enhances the images from the Magnetic
Resonance Imagining scan.
Nanoparticle can be attached to proteins or other molecules, allowing
detection of disease indicators in a lab sample at a very early stage.
One of the earliest nanomedical applications was the use of nanocrystalline
silver which acts as an antimicrobial agent for the treatment of wounds. The
nanoparticles contain nitric oxide gas, which is known to kill bacteria and
therefore can be used as a medicine for infections.
The Nanorobots could actually be programmed to repair specific diseased
cells, functioning in a similar way to antibodies in our natural healing
processes.
Antimicrobial coatings helps to minimize the spreading of microbes like
bacteria, virus and fungi. Silver and titanium dioxide nanoparticles can kill
the microbes directly.
Nanotechnology leads to grow cardiac muscle tissue artificially to repair
and restore a damaged human heart.
(e)Environment
1. There are two major ways in which nanotechnology is being used to reduce
air pollution:
catalysts, which are currently in use and constantly being
improved upon; and nano-structured membranes, which are under
development.
 Catalysts can be used to enable a chemical reaction (which changes
one type of molecule to another) at lower temperatures or make the
reaction more effective.
 Nanotechnology can improve the performance and cost of catalysts
used to transform vapors escaping from cars or industrial plants into
harmless gasses.
 The catalysts made from nanoparticles have a greater surface area to
interact with the reacting chemicals than catalysts made from larger
particles. The larger surface area allows more chemicals to interact
with the catalyst simultaneously, which makes the catalyst more
effective.
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 Nanostructured membranes, on the other hand, are being developed to
separate carbon dioxide from industrial plant exhaust streams. The
plan is to create a method that can be implemented in any power plant
without more expense.
 Nanotechnology based coating materials act as permanent air purifier.
2. Nanotechnology is being used to develop solutions to three very different
problems in water quality ;
 Used for the removal of industrial water pollution, such as a cleaning
solvent called TCE, from ground water.
 Nanoparticles can be used to convert the contaminating chemical through
a chemical reaction to make it harmless.
 Another challenge is the removal of salt or metals from water.
 A deionization method using electrodes composed of nano-sized fibers
are effective for reducing the cost and energy requirements of turning salt
water into drinking water.
 The third problem concerns the fact that standard filters do not work on
virus cells. A filter only a few nanometers in diameter is currently being
developed that should be capable of removing virus cells from water.
 Some examples of nanoparticles and their role in purification of water are
listed below.
Nanoparticle
Iron nanoparticles
NanoCeram-PAC(powder
activated carbon)
Copper based nanoparticles
Uses
Clean up carbon tetrachloride
pollution in ground water
Filters capable of removing virus
Nanowire mesh
Safe removal of radioactive
pollutants in ground water
Absorb oil pills
Iron oxide nanoparticles
Clean Arsenic from ground water
Gold tipped Carbon
nanotube
To trap oil drops
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Nanosized fibers
To deionize water, for removing
salt and metals
(f) Consumer Goals
1. Making composite fabric with nano-sized particles or fibers allows
improvement of fabric properties without a significant increase in
weight, thickness, or stiffness.
2. By incorporating nanomaterials, strength of tennis racquets can be
increased which increases the control and power when you hit the ball.
3. Nanomaterials can be used to fill the voids in golf shafts, which
improve the swing of balls.
4. By using nanomaterials, air leakage from tennis balls can be minimized
so they keep their bounce longer.
5. The hydrophobic properties of nanorods exploit them as cleaning
agents. Silver ions are used in washing machines for cleaning cloths.
6. Titanium oxide nanoparticles are used to kill bacteria through a process
called photocatalysts.
7. Nanotechnology is having an impact on several aspects of food science,
from how food is grown to how it is packaged.
8. Clay nanocomposites are being used to provide an impermeable barrier
to gasses such as oxygen or carbon dioxide in lightweight bottles,
cartons and packaging films.
9. Storage bins are being produced with silver nanoparticles embedded in
the plastic.The silver nanoparticles kill bacteria from any material that
was previously stored in the bins, minimizing health risks from harmful
bacteria.
10.Nanoparticles are being developed that will deliver vitamins or other
nutrients in food and beverages without affecting the taste or
appearance. These nanoparticles actually encapsulate the nutrients and
carry them through the stomach into the bloodstream.
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11. Silicate nanoparticles provide a barrier to gasses (for example oxygen),
or moisture in a plastic film used for packing. This could reduce the
possibility of spoiling or drying out of food.
12. Zinc oxide nanoparticles can be incorporated into plastic packing to
block UV rays and provide anti bacterial protection, while improving
the strength and stability of the plastic film.
13.Used for the preparation of cosmetic powder, spray perfumes and
deodorants.
14.Nano coating paints are more durable.
Side Effects of Nanotechnology
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REFERENCES
1.
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5.
6.
A TEXTBOOK OF ENGINEERING PHYSICS : PROF. A.ATMAJAN, TESSY ISSAC
ADVANCED PHYSICS FOR ENGINEERS
: Dr. M.C. SANTHOSH KUMAR
ENGINEERING PHYSICS
: A. MARIKANI
ENGINEERING PHYSICS
: P.K.PALANISWAMY
ENGINEERING PHYSICS
:RANBHIR SINGH, SRELATHA MENON
PHYSICS FOR ENGINEERS
: B.PREMLET