Nanophysics

LEARNING OBJECTIVES
1. Introduction
2. Classification of Nanostructures
3. Synthesis
4. Properties and Application of Nanomaterials
5. Carbon Nanotubes (CNTS)
6. Structure of Carbon Nanotubes
7. Fabrication of Carbon Nanotubes
8. Properties and Application of Carbon Nanotubes

1. Introduction
What is nano physics?
the physics of structures and artefacts with
dimensions in the nanometer range or of
phenomena occurring in nanoseconds.
What is Nanoscience?
Nanoscience is the study of atoms, molecules
and object whose size is of the nanometer scale
(1-100nm).

What is Nanotechnology?
Nanotechnology is the technique of design,
production of devices and systems by controlling
the shape and size at the nanometer scale.
What is a Nanoparticle?
A particle with size in the range of 1-100nm.
What is Nanomaterials?
Nanomaterials are the materials containing
nanocrystals, i.e. their grain size is in the 1-100nm
range. The Nanomaterials may be Metals, Alloys,
Intermetallics and Ceramic.

 Some Nanomaterials occur naturally. But of
particular interest are, engineered Nanomaterials
which are developed for use in many commercial
products and medical field. For example ,electronic
devices, sporting goods, cosmetics, textile, paint,
diagnosis, targetad drug delivery etc.
 Nanomaterials contain only nine hundred atoms
each.
 Because of their unique microstructure, the
Nanomaterials are said to have high strength,
Hardness, formability, toughness and are more
brittle.

2. Classification of Nanostructures
 There are different classification of In
nanotechnology. The most popular mode of
nanostructure classification is according to their
dimensions on the nanoscale, in at least one
dimension(direction).
 Nanostructure can be described as :
1. Zero-dimensional(0D) 2. One-dimensional(1D)
3.Two-dimensional(2D) 4. Three-dimensional(3D)

Dimensions Criteria Examples
Zero dimensional
(0-D)
The nanostructure has
all dimensions in the
nanometer range.
Nanoparticles,
quantum dots,
nanodots
One Dimensional
(1-D)
One dimension of the
nanostructure is
outside the nanometer
range.
Nanowires,
nanorods,
nanotubes
Two Dimensional
(2-D)
Two dimensions of
the nanostructure are
range.
Coatings,
thin-film-
multilayer
Three Dimensional
(3-D)
Three dimensions of
the nanostructure are
range.
Bulk

Classification of Nanomaterials (a) 0D spheres and
clusters (b) 1D nanofibers, wires, and rods, (c) 2D
films, plates, and networks, (d) 3D nanomaterials.
a b
c d

3. SYNTHESIS
Nanomaterials are basically carbon structures.
Some of the well known nanomaterials are fullerene,
carbon nanotubes and other Nanoparticles.
Fullerene Carbon nanotubes

 Using a variety of synthesis method , it is possible
to produce nanostructured materials in the form of
Thin films, Coatings, Powder, and as a Bulk
materials.
 The methods used for the synthesis of Nanoparticles
can be classified into physical, chemical, biological,
self assembly and hybrid methods. Irrespective of
the method of synthesising, it is very important to
consider their stability in the terms of their compo-
sition as well as their size.

o Classification of Synthesis Methods
 The methods for the synthesis
of nanomaterials are
classified into two process.
1. Top-down process
2. Bottom-up process
 Both the process can be done
in Gas, liquid, solid state or
in vacuum

 The Top-down process involves, the breaking
down of a bulk material to generate the required
smaller and smaller nanostructured material
through etching or milling from the bulk material.
 The bottom-up process of building up of the atom
or molecular constituents into a larger
nanostructured material. The bottom up approach
is a powerful approach of creating identical
structures with atomic Precision.

o Technique used in synthesis of nanomaterials
 various techniques are adopted for the synthesis of
nanomaterials based on the two process, top-down
and bottom-up
Let us see ,some of them.
Top-down process Bottom-up process
Milling Plasma assisted deposition process
Lithographic Vapour deposition methods
Machining Liquid phase process
Molecular Beam Epitaxy (MBE)
Laser synthesis, etc.

1. Plasma-Arcing
 Plasma is hot ionised gas.
 The experimental set-up of an arc plasma method
Is shown in the Figure.
 The arc plasma set up consist of a pair electrodes
(a anode and a cathode) with a gap approximately
One mm.
 The anode electrode itself acts as the source of
materials and the other electrode acts as a
substrate.

Plasma torch Plasma arc Plasma welding

 The electrode are kept in high vacuum or ultra high
vacuum enclosure filled with an inert gas
(He or Ar) at 100-500 torr.
 When a high current approximately 50 to 100 A is
passed from a low voltage power supply, a high
discharge is created between the two electrodes.
 Temperature as high as approximately 3500 ºC
reaches as arc discharge takes place.
 Thus; when an arc is set up, anode material
evaporates.

 These positive ions are attracted towards the
other electrode and get deposited over it to form
thin films of Nanoparticles.
 The anode material evaporation continues as
long As the discharges is maintained.
 The adjustment of the electrode gap without
breaking the vacuum becomes essential as one of
the electrode burns and gap increases.
 This method is mostly found to be suitable for
fullerenes or carbon nanotubes deposition.

2. Vapour phase Deposition
 In general, there are two classes of vapour phase
Deposition.
1. Physical Vapour Deposition(PVD)
2. Chemical Vapour Deposition(CVD)
 PVD process involves the direct deposition of
gaseous phase over the substrate surface.
 But CVD process involves, either the chemical
reaction or thermal decomposition of gas phase at
elevated temperature and subsequent deposition
onto a substrate.

o Chemical Vapour Deposition
 Principle :
Chemical vapour deposition is a process, which
involves the flow of a gas with diffused reactants
over a hot substrate surface
 Description and Working :
 A typical thermal CVD apparatus comprises of gas
Supplying system, deposition chamber and an
exhaust system.
 The entire assembly is called a reactor.

 There are two types of thermal CVD reactor which
are used to perform CVD process.
1. Horizontal reactor
2. Vertical reactor
 The schematic representation of a horizontal
reactor CVD is shown in figure.
 In the reactor shown, The substrate surface is
raised to a very high temperature with the help of
resistance Heater.
 The resistance heater either surround the chamber
or lie directly under the susceptor that holds the
substrates.

 In thermal CVD process, the chemical reactions is
activated by a high temperature above 900ºC.
 In this technique, the material to be deposited is
heated to form a gas phase and is subsequently
deposited on to a heated substrate.
 While the gas flows over the hot solid substrate,
the heat energy activates the chemical reaction at
appropriate site, nucleate and grow to form the
desired material film.
 The by products created on the substrate are then
properly vented with the help of an outlet.
 The gas that carries the reactants is called gas.

 Note :
1. In thermal CVD : The reaction is activated by a
high
temperature > 900ºC.
2. In plasma CVD : The reaction is activated by a
plasma
at temperature between 300ºC and 700ºC.
3. In laser CVD : The pyrolysis occurs by a laser
beam.
4. In photolaser CVD : The chemical reaction is
induced
by ultraviolet radiation.

o Merits
1. CVD technique is very simple in design.
Hence used for mass production in industry.
2. It is used to produce defect free
Nanoparticles.

3. Sol-Gel Technique
 In this technique, nitrates or carbonates are taken as
pre Cursors which are dissolved in deionized water.
 The solution is kept at a suitable temperature and
some amount of gelling agents are added to it.
 Thus, the viscosity, temperature and PH of the
solution is controlled in this technique.
 The nanomaterials in the form of thin film coatings
are made by this technique.
 For thin film coating, substrates like copper, nickel,
or glass are taken and dipped in the solution before
gel formation. Finally, annealing has to be done to
get thin films.

Schematic representation of sol-gel process of synthesis of nanomaterials.

 The sol gel synthesis is most widely used due to the
following reasons.
1. In this technique; materials, both ceramic and metals
can be produced at ultra low temperature.
2. Any type of material can be synthesized in large
quantities very cheaply.
3. Extremely homogeneous alloys and composites can
be produced.

4. High purity (99.9999%) in synthesized materials
can be obtained.
5. In this technique, the microstructure and physical,
chemical and mechanical properties of the final
products can be controlled.
6. Co-synthesis of two or more materials
simultaneously is possible.

4. Electro Deposition (ED)
 Electro deposition ED is a unique technique in
which a variety of materials can be processed .
 It includes; metals, ceramics and polymers.
 Using this technique, it is possible to obtain pore-
free nanocrystalline metal specimens in a single
step process.
Note :
 Electrolyte : A solution or molten substance that
conducts electricity.

Description and working :
 A general schematic diagram of the ED process is
shown in the figure.
 The apparatus consists of two electrodes a anode
and cathode.
 The electrodes are immersed in the deposition
solution as shown in the figure 1.
 The two electrodes are connected to a battery to
pass the current.
 When the current is passed through the electrodes,
certain mass of substance from anode will get
liberated and is deposited on the surface of
cathode.

Figure 1. Electrodeposition
Figure 2.

 Hence, a thin nanofilm gets formed on the surface
of other electrode (cathode).
 The thickness of the film can be adjusted by
controlling the current and time of deposition.
 To obtain enhanced characteristic of any
nanocoating, it is essential to select an appropriate
anode and cathode materials with a suitable
coating to be used as electrodes.
 In addition, it is essential to optimise the
electrolyte composition as well as the deposition
parameter.

Advantages
1. No post deposition treatment.
2. Free from porosity and high purity.
3. Low cost.
4. Easy to control alloy composition and higher
deposition rates.
5. Ability to produce structural features and
composition unattainable by other technique.
6. It is possible to produce coating on widely
different substrates.

7. Formation of simple, low-cost multilayer of
different system, Ni/Ni-P, Cu/Ni, etc., is possible.
Uses
1. It is used to produce industrially important
materials such as Ni, Ni-P, Ni-Mo, Cu etc.
2. It is used to prepare novel hybrid nanomaterials.

5.Ball Milling (mechanical Crushing)
 Ball milling technique produces Nanoparticles by
collisions of balls with the fine powdered particles.
 This process is executed in a repeated manner to get
Nanoparticles.
 The grain size in powder sample are reduced to
nanometer range by mechanical deformation.
 The most industrial important technique in
fabricating nanomaterials is high energy ball
milling. Also known as mechanical alloying or
mechanical attrition.

 It is solid state process used for the manufacture of
a wide range of nanopowder.
 This high energy ball process induces structural
changes and chemical reaction at room
temperature.
 The mechanical crushing of powder material is
done by placing the material inside a rotating
stainless steel drum with hard steel or tungsten
carbide balls as shown in the figure 1.
 Thus on rotating steel drum, the hard balls crush
the powder materials mechanically.

Figure 1. Rolling ball milling
High energy ball milling

 This repeated deformation can cause large
reduction in grain size in the powder particles as
shown in the figure 2.
 Different components can be mechanically alloyed
together by cold welding to produce
nanostructured alloys.
 Mechanical crushing is performed under
controlled atmospheric conditions to prevent
unwanted reactions such as oxidation.

Merits
1. This technique can be operated in large scale.
2. In a short time, few milligram to several
kilograms of Nanoparticles can be synthesised.
3. Fabrication of alloys which can not be produced
by conventional techniques can be done using
this method.

Demerits
1. The nanomaterials produced by this method is
contaminated with impurities.
2. This technique also produces a variety of non-
equilibrium structure that include amorphous,
quasi-crystalline and nanocrystalline materials
Uses
1. High energy mechanical milling is a very effective
process for synthesising metal-ceramic composite
powder.
2. It Is also used for the production of
nanocomposites, nanotubes, nanorods, nanowires,
etc.

4. Properties of nanomaterials
1. The nanomaterials have high strength,
hardness, formability and toughness.
2. These materials are more brittle.
3. These materials exhibit super plasticity even at
lower temperatures.
4. Magnetic moment of nanomaterials can be
increased by decreasing the particle size.
5. Optical density of these materials can be varied
with the diameter.

6. The melting point of nanomaterials gets reduced
on reducing the grain size.
7. Size of the grains; controls the mechanical,
electrical, optical, chemical, semiconducting and
magnetic properties.
8. The magnetization and coercivity are higher.

Disadvantages of Nanomaterials
1. Impurity : Since nanomaterials are highly
reactive, they inherently interact with impurities
as well. In addition, encapsulation of
nanoparticles become necessary whey they are
synthesised in a solution.
2. Difficulty in synthesis, isolation and application :
It is extremely hard to retain the size of
nanoparticles once they are synthesised in a
solution.

3. Instability of the particles : Retaining the active
metal nanoparticles is highly challenging, as the
kinetics associated with nanomaterials is rapid.
4. Nanoparticles are small enough to be absorbed
by the skin and cause irritation and have
indicated to be carcinogenic.
5. Breathing in any fine or tiny solid particles can
cause irritation lungs and can cause lung damage
and cancer. Example, coal workers
6. Chemicals in the form of tiny nanoparticles have
been shown to spread throughout the a crop plant
and affect growth and soil fertility.

7. Nanosilver particles kill bacteria. But they kill
good non-bacterial cells or good bacteria if it is
inhaled or ingested.
8. Fine metals particles act as strong explosive
owing to their high surface area coming in direct
contact with oxygen. Their exothermic
combustion can easily cause explosion.
9. There are no hard and fast safe disposal policies
evloved for nanomaterials.
10. Nanomaterials are more costly to produce
compared to more traditional bulk materials.

Application of Nanomaterials
1. Nanomaterials are used for the fabrication of
signal processing elements such as filters, delay
lines, switches etc.
2. Using these materials, soft and permanent
magnets can be manufactured which is said to
have a wider application.
3. Nanocrystalline materials like tungsten carbide,
tantalum carbide and titanium carbide are used in
making cutting tools. These tools are much harder
and lasts longer than their conventional (large
grained) counter parts.

4. These materials are used to make semiconductor
lasers, nanotransistor, memory devices such as
recording heads and magnetic storage devices etc.
5. Hydrogen based sensor made by nanomaterials
are used in power generation.
6. Nanomaterials are used for manufacturing of
small size, light weight microstrip patch antennas.
These miniaturized antennas are said to have
large bandwidth, tunability and mechanical
flexibility.
7. These materials are used in enzyme removal of
CO2 from air and waste water treatment.

8. Nanocrystalline ZNO thermistors are used in
current controlling devices.
9. SiC nanocrystalline is used in making artificial
heart valves due to its weight, high strength,
inertness, extreme hardness and wear resistance.
10. When nanocrystalline ceramics such as zirconia
and alumina are used as liners in automobile
engine cylinders, they help in retaining heat much
more efficiently and result in complete and
efficient combustion of the fuel.
 The application of nanomaterials are not limited
only to the above mentioned. There are a large
number of application and uses of it.

5. Carbon Nanotubes (CNTS)
 The more interesting nanostructures with large
application potential are carbon nanotubes(CNTs).
 In 1991,Sumio Iijima discovered CNTs.
 CNTs are also known as bucky tubes.
 They are allotropes of carbon with a cylindrical
nanostructure.

What is a Carbon Nanotubes?
 A single sheet of graphite atoms arranged in a
hexagonal lattice pattern(below Figure) is called as
graphene.
Graphene sheet

 A carbon nanotubes is a cylindrical rolled up sheet
of graphene mostly closed at the ends.
 The rolled structure is a single molecule. Each
single molecule nanotubes is made up of
hexagonal network structure of covalently bonded
carbon atoms. The next figure shows the structure
of a carbon nanotubes formed by rolling the
graphene sheet.
 Their hexagonal structure gives them great tensile
strength and elastic properties.

Rolled graphite sheet to obtain CNT.

 Nanotubes are members of the fullerene structural
family, which also includes the spherical bucky
balls.
 The ends of nanotubes may be capped with a
hemisphere of the bucky ball stucture.These are
simply called as “caps” or “end caps”.
 Caps contain six pentagons and different number
of hexagons so that they can fit on the tubes
properly.
 Carbon nanotubes are categorised as :
1. Single Walled Carbon Nanotubes (SWCNTs)
2. Multi-Walled Carbon Nanotubes (MWCNTs)

6. Structure of the CNTs
 Depending on folding of graphite sheet, the
structure of CNTs (SWCNTs) are classified as,
1. Armchair
2. Zigzag
3. Helical or Chiral, under appropriate conditions.

7. Fabrication of CNTs
 The CNT are fabricated primarily using,
1. Electric arc
2. Chemical vapour deposition
3. Pulsed laser deposition technique
 In this section, all three techniques are discussed
in brief.

1.Electric Arc Method (Carbon arc Method
 The electric arc method or carbon arc evaporation
method produces the best quality of nanotubes.
 This is most common and perhaps the easiest and
simple way to produce CNTs.
 This method is also called plasma arching method
or DC Arc Discharge (DCAD) method.
 We have seen this method in synthesis of
nanomaterials.
 Nanotubes with a diameter from 2 to 30 nm and
1µm length can be produced by this method.

 To produce MWCNT’s it is not necessary to use
any catalyst.
 But to produce a SWCNT it is necessary to use a
catalyst added to the anode.
 Fe, Co, Ni or some other metals can be used as
catalyst.

2. Chemical Vapour Deposition Method
 The chemical vapour deposition method involves
decomposing a hydrocarbon gas such as methane
(CH4), at 1100ºC or ethane (C6H6), etc.
 For large scale production of carbon fibers and
filaments, this method is most useful.
 Description and Working
 The experimental set up is shown in the Figure.
 The experimental set-up consist of a high
temperature evacuated reaction vacuum furnace.

C2H2
N2
Vacuum
pump
Chemical vapour deposition

 The vacuum is produced inside the furnace with the
help of a vacuum pump connected to the furnace.
 There is also a provision to maintain inert
atmosphere.
 Inside the furnace, a substrate prepared with a layer
of metal catalyst such Fe, Co or Ni is placed.
 There is also an another provision in the furnace to
allow two types of gases to initiate the growth of
CNTs.
 One type of gas is a process gas like ammonia ,
nitrogen , hydrogen , etc., and the other a carbon
containing gas such as methane, acetylene, etc.

 The hydrocarbon gas such as methane is passed
into the furnace.
 The furnace is heated to approximately 750ºC to
1100ºC, based on the selection of hydrocarbon.
 At this high temperature, the gas decomposes
producing carbon atoms which get deposited over
the catalytic substrate forming nanotubes.
 The catalyst plays a very important role in CNT
formation.
 This method of production allows continuous
fabrication of nanotubes with open ends which
does not occur in other methods.

 The diameter of the CNTs formation depend on
the thickness of the catalytic film over the
substrate.
Merits
1. Both SWCNT and MWCNT’s are possible to
obtain by this method.
2. High purity CNTs can be produced due to the
non formation of nanoparticles or amorphous
carbon.
3. Aligned CNTs can be deposited over the solid
substrate which has major application in
electronics field.

3. Pulsed Laser Deposition
 With the help of pulsed laser beam, SWCNT’s can
be prepared by laser vapourisation of a graphite
rod.
Description and working
 The schematic sketch of the pulsed laser
deposition set-up is shown in the Figure.
 The apparatus consists of a quartz tube filled with
Ar gas under a pressure of 500 torr.
 A graphite target doped with small amount of
catalyst like Co, Fe, or Ni to act as catalytic
nucleation sites for the formation of CNT is also
placed inside the quartz tube.

Water cooled
Cu collector
1200ºC furnace
Nd:YAG
laser
Pulsed laser deposition
Quartz tubeGraphite target

 The quartz tube containing the Ar gas and a
graphite target is heated to 1200ºC.
 Inside the quartz tube a water cooled copper
collector is placed at the other end just away from
the furnace.
 When a highly intense pulsed laser beam produced
from a Nd:YAG laser source is incident on the
target, it evaporates carbon from the target
graphite.
 The Ar gas sweeps the evaporated carbon atoms
from the high temperature zone to the low
temperature zone where they condense into
nanotubes.

 In this method, the dual pulsed laser beam
minimises the amount of carbon deposited as soot.
 The initial laser vapourisation pulse is followed by
a second pulse to vapourise the target more
uniformly.
 The second laser pulse breaks up the larger
particles ablated by the first one and feeds them
into the growing nanotubes structure.

Merits
1. In this method, CNT ropes of 10-20nm in
diameter with a length of 100mm can be
produced. The tube diameter can be controlled
by the reaction temperature. More than 85%
graphite is converted into CNTs.

8. Properties of CNTs
1. The carbon nanotubes have extremely low
resistance.
2. The conductivity of nanotubes is a function of
diameter.
3. CNTs are metallic or semiconducting depending
on the diameter and chirality of the tube.
4. Metallic nanotubes can carry an electric current
which is more than 1000 times greater than metal
copper.

5. CNTs have a high thermal conductivity which
increases with decrease in diameter.
6. CNTs melting temperature is three times higher
than the melting point of copper.
7. CNTs have the ability to withstand extreme
strain.
8. Nanotubes are highly resistant to chemical attack.
9. Nanotubes have a high strength to weight ratio.
This is indeed useful for light-weight application.
10. The tensile strength is more than 20 times greater
than steel.

Application of CNTs
1. CNTs are used in constructing nanoscale
electronic devices.
2. CNTs are used in battery electrodes, electrical
devices, reinforcing fibres which make stronger
composites.
3. The electron emission concept of CNTs are used
in developing a flat-panel display.
4. Based on the electron emission effect of CNTs,
vacuum tube lamps that are bright as
conventional light bulbs with longer life and
more efficiency can be produced.

5. Semiconducting CNTs are used as switching
devices and display devices.
6. Chiral semiconducting carbon nanotubes are used
as sensitive detector of various gases.
7. CNTs are used in battery technology to design
fuel cells.
8. Nanotubes tips can be used as nanoprobes.
9. Nanotubes serve as catalyst for some chemical
reaction.
10. CNTs are used as interconnects in chip due to
their extremely low resistance.

11. The CNTs can be used to build tiny electronic
circuits which are almost 1000 times smaller than
today’s technology.
12. A plastic composite of CNTs are used in
designing a light-weight shielding material for
electromagnetic radiation.

Summary
 In the field of electrical, electronic, optical,
medical and communication materials play a vital
role.
 Nanomaterials are the materials having grain size
in the range 1 to100nm.
 Nanomaterials are more brittle, have high strength,
hardness, toughness and exhibit super plasticity.
 Nanomaterials find a wide application in the field
of medicine and electronics.

 A single sheet of graphite atoms arranged in a
hexagonal lattice pattern is called as graphene.
 Depending on folding of graphite sheet, the
structure of CNTs (SWCNTs) are classified as,
armchair, zigzag and helical or chiral under
appropriate conditions.
 CNTs find a wide range of application in many
different fields.

Check your self
1. What is nanoscience?
2. What is nanotechnology?
3. What is Nanoparticle?
4. What is the range of particle size in nano
structured materials?
5. Classify only name of the nanostructure
according to their dimensions.
6. Give the name of the synthesis method of
nanomaterials.

7. What are the carbon nanotubes?
8. Mention different forms of nanomaterials.
9. Classify the synthesis methods of carbon
nanotubes.
10. Mention the different structure of carbon
nanotubes.
11. Give the full form of the below.
1.SWCNTs
2.MWCNTs

Reference
 G Vijyakumari
 www.vikas publishing.com
 A. Alagarasi
 http://www.nano.gov
 http://www.nano-and-society.org/
 http://www.springer.com

Nanophysics

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