nano materials

7182019 Nano Materials

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Unit ndashV Nano-materials Engineering Physics

Dr PSreenivasula Reddy MSc PhD Website wwwengineeeringphysicsweeblycom

IntroductionIn recent years nanotechnology has become one of the most important and

exiting forefront fields in physics chemistry biology and engineering and technologyNano means 983089983088m A nanometer (nm) is one thousand millionth of a meter Atomsare extremely small and the diameter of a single atom varies from 01 to 05 nmdepending on the type of the element For example one carbon atom is approximately015nm in diameter and a water molecule is almost 03nm across A red blood cell isapproximately 7000 nm wide and human hair is 80000 nm wide

Origin of Nano technologyWhile the word nano technology is relatively new the existence of nanostructures

and nanodevices is not new Such structures existed on the earth as life itself Thoughit is not known when humans began to use nanosized materials the first known Romanglassmakers were fabricated glasses containing nanosized metalsWhen the material size of the object is reduced to nanoscale then it exhibits differentproperties than the same material in bulk form

NanoscienceNano science deals with the study of properties of materials at nano scales whereproperties differ significantly than those at larger scale

Nanotechnology

Nanotechnology deals with the design characterization production and applications ofnanostructures and nanodevices and nanosystems

1 Nano materials

All materials are composed of grains The visibility of grains depends on their

size Convectional materials have grains varying in size from hundreds of microns to

millimeters The materials processing grains size ranging from 1 to 100 nm known as

nano materials Nano materials can be produced in different dimensionalities These

are classified as

One dimensional nano materials

Two dimensional nano materials

Three dimensional nano materials

One dimensional nano materials

In this the grains will be layered in the form of multi layers such as thin films or

surface coatings

Two dimensional nano materials

In this the ultrafine grains will be layered such as nano wires or nano tubes

Three dimensional nano materials

In this the grains will be in nano size such as precipitates and colloids

2 Basic principles of nano materials

When the material size of the object is reduced to nanoscale then it exhibitsdifferent properties than the same material in bulk form The factors that differentiatesthe nanomaterials form bulk material is

1 Increase in surface area to volume ratio

2 Quantum confinement effect




Increase in surface area to volume ratioThe ratio of surface area to volume ratio is large for nano materialsExample 1 To understand this let us consider a spherical material of radius lsquorrsquo Then its

surface area to volume ratio is

Due to decrease of r the ratio increases

predominantlyExample 2 For one cubic volume the surface ratio is 6m2 When it is divided into eight

cubes its surface area becomes 12 m2

When it is divided into 27 cubes its surface areabecomes 18m2 Thus when the given volume is divided into smaller pieces the surfacearea increases

Due to increase of surface of surface area more number of atoms will appear at the

surface of compared to those inside For example a nano material of size 10nm has

20 of its atoms on its surface and 3nm has 50 of its atoms This makes the

nanomaterials more chemically reactive and affects the properties of nano materials

Quantum confinement effect

According to band theory the solid atoms have energy bands and isolated atoms

possess discrete energy levels Nano materials are the intermediate state to solids and

atoms When the material size is reduced to nanoscale the energy levels of electrons

change This effect is called quantum confinement effect This affects the optical

electrical and magnetic properties of nanomaterials

3 Fabrication methods of nanomaterials

The nanomaterials can be synthesized in two ways namely

Bottom ndashup approach and

Top-down approachBottom-up approach

In this method the nanomaterials are synthesized by assembling the atoms and

molecules together

Examples Sol-gel method

Chemical vapour deposition

Thermal vapour deposition

Plasma arcing

Top-down approach

In this method the nanomaterials are synthesized by dis-assembling the solids

into finer pieces until the particles are in the order of nanometersExamples Ball milling

4 Ball milling method

This method is a very popular simple inexpensive and scalable method This is

also called crushing method Ball method is to prepare a wide range of elemental and

oxide powders This method is to produce nanocrystalline or amorphous materials

When the balls are allowed to rotate with particular rpm inside of a drum the

necessary energy is transferred to the powder which in turn reduces the powder grain-

sized structure to ultrafine or nano range particles Depending on the material either




powder from the balls depends on many factors such as rotational speed of the balls

number of balls milling time and the milling medium

Generally a hard material will be selected to synthesize softer material

Commonly alumina and zirconica balls are used to synthesize the nanomaterials

5 Chemical vapour deposition

In chemical vapour deposition is a well known process in which a solid isdeposited on a cooled surface via chemical reaction from vapor or gas phase Thebasic steps involved in this process are (i) Generation of vapour by boiling or subliminga source material (ii) Transformation of the vapour from the source to the substrate and(iii) Condensation of vapour on the cool substrateIn this method the atoms are molecules are in gases state allowed to reacthomogenously or heterogeneously depending on the applications This method is anexcellent method which is used to control the particle size shape and chemicalcompositions

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Dr PSreenivasula Reddy MSc PhD Website wwwengineeeringphysicsweeblycom Page 4

This method is used to produce the nano powders of oxides and carbides of metalsProduction of pure metal powders is also possible using this method

6 Sol-gel method

Sol-gel method is one of the bottom up approach for the fabrication ofnanoparticles by assembling the atoms The sol-gel process is a wet technique ie

chemical solution deposition technique used for the production of high purity andhomogeneous nanomaterials In solutions the molecules of nanometer size aredispersed and move around randomly and hence the solution are clear In colloids themolecules of size ranging from 983090983088 to 983089983088983088 are suspended in a solvent Whenmixed with a liquid is called as sol A suspension that keeps its shape is called a gelThus the colloids are suspensions of colloids in liquids that keep their shape Theformation of sol-gels involves four steps

a) Hydrolysis and alcoholysisb) Water or alcohol condensation and polymerization of monomers to form particlesc) Growth of particles andd) Formation of networks

In general all the above steps are dependent on several initial conditions such

as pH

value of the sol temperature of reaction reagent concentrations time ofreaction etc by controlling these parameters it is possible to vary the structuralelectrical and optical properties of the sol-gel derived inorganic networks over a widerange

Once the gel is formed there are several ways to convert this gel to the desiredsolid form Depending on the deposition and drying processes or conditions this gelcan be converted into various forms such as aerogel xerogel gelled spheres nanopowders thin film coatings nano structured layers etc as shown in the figure



Unit ndashV

7 Plasma arching met

Plasma is an ioniapplied across the electroyields up its electrons andelectrode (cathode) pickthis plasma arching meth

deposited on the surfaceinert gas By using carboof the cathode

8 Thermal vapour dIn thermal vapour

refractory metals like Wceramic materials When

amount of thermal energyadequately it begins to esubstrate is to be coated

In higher vacuum tare less number of moleand a longer mean freebefore striking an unwant

The rate of depositifilament The schematic di

Nano-materials Enginee

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ed gas To produce plasma high potes An arc passes from one electrode topositive ions at anode Positively chargep electrons and are deposited to form naod very thin films of the order of atomic

f an electrode This deposition is carriedn electrodes carbon nanotubes can be for

positioneposition method the sample is taken ino Ta etc or heat shielded crucible ma

high current is passing through the filame

is produced When the substrate (targetaporate and travel through the chamber a

he material will be deposited will be moreules in the chamber which will increase tath will allow the evaporated the moleculd molecule in the chamberon can be controlled by the current beingagram of thermal vapour deposition is sho

ing Physics

ntial difference isanother The gasions pass to othero particles Usingimensions can be

in vacuum or in aned on the surface

a boat made up ofe up of alumina ornt (boat) sufficient

material) is heatedd deposited on the

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assing through then in figure



Unit ndashV Nano-

9 Properties of nanomaterial

Physical properties

Inter atomic distance

When the material size is rincreases Due to increase of surfasurface of compared to those insidchange in the Interatomic spacingdecrease of particle is shown in figur

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Melting pointMelting point for nano mater

Debye Temperature and ferroelectrmaterials The melting point of nanparticle decreases form 300A0 todecrease of particle is shown in figur

aterials Engineering Phy

s

duced to nanoscale surface area to volce area more number of atoms will appe This changes the surface pressure andThe variation of Interatomic spacing in coe

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ials are different from that of bulk materi

ic phase transition temperature are lowergold decreases from 1200 K to 800K as t00A0 The variation of melting point ine

sics

me ratioar at theresults inper with

ls The

for nanoe size ofold with




Optical properties

Different sized nano particles scatters different of light incident on it and hencethey appear with different colours For example nano gold does not act as bulk goldThe nano particles of gold appear as orange purple red or greenish in colourdepending on their grain size The bulk copper is opaque where as nanoparticle copperis transparent The optical absorption spectrum of gold as a function of particle size is

shown in figure

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Magnetic properties

The magnetic properties of nano materials are different from that of bulk materials Inexplaining the magnetic behavior of nanomaterials we use single domains unlike largenumber of domains in bulk materials The coercivity values of single domain are verylarge The variation of remanet magnetization and coercivity as a function of grain sizeis shown in figure

For example FeCo and Ni are ferromagnetic in bulk but they exhibit super parmagnetism Na K and Rh are paramagnetic in bulk but they exhibit ferro-magneticCr is anti ferromagnetic in bulk but they exhibit super paramagnetic





Mechanical properties

The mechanical properties such as hardness toughness elastic modulus

youngrsquos modulus etc of nano materials are different from that of bulk materials In

metals and alloys the hardness and toughness are increased by reducing the size of

the nano particles In ceramics ductility and super plasticity are increased on reducing

grain size Hardness increases 4 to 6 times as one goes from bulk Cu tonanocrystalline and it is 7 to 8 times for Ni

Thermal properties

Chemical properties

Nanocrystalline materials are strong hard erosion and corrosion resistant They are

chemically active and have the following chemical properties

1 In electrochemical reactions the rate of increase in mass transport increases as

the particle size decreases

2 The equilibrium vapour pressure chemical potentials and solubilites ofnanoparticles are greater than that for the same bulk material

3 Most of the metals do not absorb hydrogen But the hydrogen absorption

increases with the decrease of cluster size in Ni Pt and Pd metals

10 Properties of carbon nanotubesCarbon nanotubes (CNT) were first observed b Sunmino Iijima in 1911 Carbon

nanotubes are obtained by rolling the graphite sheet into tubes with the bonds at the

ends of the sheet These bonds are used to close the tube Generally the length of

carbon nanotubes varies from several micrometers to millimeter and the diameter will

vary from 1 to 20 nmA tube may contain one cylindrical wall of graphite or a number of concentric

cylindrical walls A carbon nanotube consisting of one cylindrical graphite is called

single walled nanotube Otherwise they are known as multi walled nanotubes

Depending on how sheet is rolled they are classified into three types The three types

of carbon nanotubes are

1) Zigzag

2) Chiral

3) Armchair

1 All carbon nano tubes are good thermal conductors2 Carbon nanotubes exhibit magneto resistance effect

3 Carbon nanotubes have high strength and light weight

4 Metallic carbon nanotubes exhibits low specific resistivity and hence high current

density

5 Semiconducting carbon nanotubes exhibits high hole carrier mobility which in turn

produces hence high current density

6 Carbon nanotubes exhibits optical activity and hence they used in optical devices

7 They exhibit enhanced chemical reactivity





11 High strength applications of carbon nanotubes

Carbon nanotubes have large number of applications in various fields They are

I Hydrogen storage

II Thermal conductivity

III Field emission applications

IV Air water filtration

V Space elevators

VI Energy storage

VII Structural compositions

VIII Hospitalities

IX Molecular electronics

Hydrogen storage

Carbon nano tubes have high hydrogen storage capacity and also store helium

oxides metals like copper

Thermal conductivity

Carbon nanotubes are used to move the heat from one place to another forexample in case of uncooled chips

Field emission application

Carbon nanotubes are the best known field emitters because of their high electrical

conductivity and sharpness of their tips The current density in the carbon nanotubes is

in the order of 1013Acm2

Air water filtration

The carbon nanotubes based air and water filtration devices have been

developed The filters not only block small particles but also kill bacteria

Space elevators

Carbon nanotubes have less weight so they are used in aero planes spaceshipsand land vehicles Carbon nanotubes like graphite can withstand high temperatures so

they are used for thermal protection of space craft during re entry into the atmosphere

Energy storage

Carbon nanotubes are used as electrodes in batteries and capacitors Carbon

nanotubes are used in super capacitor electrodes and in a variety of fuel cell Carbon

nanotubes can be used in Lithium-ion batteries

Structural compositions

The carbon nanotubes possess high strength toughness and stiffness and hence

they find in a good number of structural applications Nanotubes can be act as axels

Hospitalities

Carbon nanotubes are thin so they can penetrate the skin without pain Blood

can be drawn from diabetic patients through nano straws to know glucose levels and to

inject insulin whenever required

Molecular electronics

The carbon nanotubes are used as inter connections between switches and other

active devices in molecular electronics Single walled carbon nanotubes are act as

transistor A single nanotube with natural junction acts as rectifying diode





12

Properties of Graphene

Graphene is a one-atom-thick planar sheer of SP2-bonded carbon atoms that are

densely packed in a honeycomb crystal lattice The C-C bond length in Graphene is

approximately 142Ao

1 The expected structure of Graphene is hexagonal structure

2 Intrinsic Graphene is a semi-metal or zero-gap semiconductor

3 It exhibits high electron mobility at room temperature

4 It exhibit high opacity

5 It exhibit high thermal conductivity at room temperature

6 It exhibit high Youngrsquos modulus hence it is very strong and rigid

7 It exhibit high carrier mobility hence it is used as the channel in FET

13 Applications of nanomaterials

Nano materials posses unique and beneficial physical chemical and mechanicalproperties they can be used for a wide verity of applications

Material technology

Nanocrystalline aerogel are light weight and porous so they are used for

insulation in offices homes etc

Cutting tools made of nanocrystalline materials are much harder much more

wear- resistance and last stranger

Nanocrystalline material sensors are used for smoke detectors ice detectors

on air crfr wings etc

Nanocrystalline materials are used for high energy density storage batteries

Nanosized titanium dioxide and zinc dioxide are used in sunscreens to absorband reflect ultraviolet rays

Nan coating of highly activated titanium dioxide acts as water repellent and

antibacterial

The hardness of metals can be predominately enhanced by using

nanoparticles

Nanoparticles in paints change colour in response to change in temperature

or chemical environment and reduce the infrared absorption and heat loss

Nanocrystalline ceramics are used in automotive industry as high strength

springs ball bearings and valve lifters

Information technology

Nanoscale fabricated magnetic materials are used in data storage

Nano computer chips reduce the size of the computer

Nanocrystalline starting light emitting phosphors are used for flat panel

displays

Nanoparticles are used for information storage

Nanophotonic crystals are used in chemical optical computers




Biomedicals

Biosensitive nanomaterials are used for ragging of DNA and DNA chips In the medical field nanomaterials are used for disease diagnosis drug

deliveryaand molecular imaging Nanocrystalline silicon carbide is used for artificial heart valves due to its low

weight and high strength

Energy storage

Nanoparticles are used hydrogen storage

Nano particles are used in magnetic refrigeration

Metal nanoparticles are useful in fabrication of ionic batteries

14 Graphene based FET




Increase in surface area to volume ratioThe ratio of surface area to volume ratio is large for nano materialsExample 1 To understand this let us consider a spherical material of radius lsquorrsquo Then its

surface area to volume ratio is

Due to decrease of r the ratio increases

predominantlyExample 2 For one cubic volume the surface ratio is 6m2 When it is divided into eight

cubes its surface area becomes 12 m2

When it is divided into 27 cubes its surface areabecomes 18m2 Thus when the given volume is divided into smaller pieces the surfacearea increases

Due to increase of surface of surface area more number of atoms will appear at the

surface of compared to those inside For example a nano material of size 10nm has

20 of its atoms on its surface and 3nm has 50 of its atoms This makes the

nanomaterials more chemically reactive and affects the properties of nano materials

Quantum confinement effect

According to band theory the solid atoms have energy bands and isolated atoms

possess discrete energy levels Nano materials are the intermediate state to solids and

atoms When the material size is reduced to nanoscale the energy levels of electrons

change This effect is called quantum confinement effect This affects the optical

electrical and magnetic properties of nanomaterials

3 Fabrication methods of nanomaterials

The nanomaterials can be synthesized in two ways namely

Bottom ndashup approach and

Top-down approachBottom-up approach

In this method the nanomaterials are synthesized by assembling the atoms and

molecules together

Examples Sol-gel method

Chemical vapour deposition

Thermal vapour deposition

Plasma arcing

Top-down approach

In this method the nanomaterials are synthesized by dis-assembling the solids

into finer pieces until the particles are in the order of nanometersExamples Ball milling

4 Ball milling method

This method is a very popular simple inexpensive and scalable method This is

also called crushing method Ball method is to prepare a wide range of elemental and

oxide powders This method is to produce nanocrystalline or amorphous materials

When the balls are allowed to rotate with particular rpm inside of a drum the

necessary energy is transferred to the powder which in turn reduces the powder grain-

sized structure to ultrafine or nano range particles Depending on the material either










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Thermal properties

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Chemical properties

















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3) Armchair




density











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Thermal properties

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1) Zigzag

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density











I Hydrogen storage




V Space elevators

VI Energy storage


VIII Hospitalities


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displays






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Physical properties



983088983086983090

983088983086983090983089

983088983086983090983090

983088983086983090983091

983088983086983090983092

983088983086983090983093

983088983086983090983094

983089983086983088983088

983145 983150 983156 983141 983154 983137 983156 983151 983149

983145 983139 983155 983152 983137 983139 983145 983150 983143




s


983090983086983088983088 983091983086983088983088 983092983086983088983088 983093983086983088983088

983108983145983137983149983141983156983141983154 983150983149



sics


ls The





Optical properties


shown in figure

983088

983089983088

983090983088

983091983088

983092983088

983093983088

983094983088

983095983088

983096983088

983097983088

983089983088983088

983092983088983088 983092983093983088 983093983088983088 983093983093983088 983094983088983088 983094983093983088 983095983088983088

983105 983138 983155 983151 983154 983152 983156 983145 983151 983150

983127983137983158983141 983148983141983150983143983156983144 983150983149

983090983088 983150983149

983094983088 983150983149

Magnetic properties













Thermal properties

Chemical properties

















1) Zigzag

2) Chiral

3) Armchair




density











I Hydrogen storage




V Space elevators

VI Energy storage


VIII Hospitalities


Hydrogen storage












Space elevators



Energy storage







Hospitalities












12




approximately 142Ao










Material technology










antibacterial


nanoparticles









displays






Biomedicals




Energy storage








Optical properties


shown in figure

983088

983089983088

983090983088

983091983088

983092983088

983093983088

983094983088

983095983088

983096983088

983097983088

983089983088983088

983092983088983088 983092983093983088 983093983088983088 983093983093983088 983094983088983088 983094983093983088 983095983088983088

983105 983138 983155 983151 983154 983152 983156 983145 983151 983150

983127983137983158983141 983148983141983150983143983156983144 983150983149

983090983088 983150983149

983094983088 983150983149

Magnetic properties













Thermal properties

Chemical properties

















1) Zigzag

2) Chiral

3) Armchair




density











I Hydrogen storage




V Space elevators

VI Energy storage


VIII Hospitalities


Hydrogen storage












Space elevators



Energy storage







Hospitalities












12




approximately 142Ao










Material technology










antibacterial


nanoparticles









displays






Biomedicals




Energy storage















Thermal properties

Chemical properties

















1) Zigzag

2) Chiral

3) Armchair




density











I Hydrogen storage




V Space elevators

VI Energy storage


VIII Hospitalities


Hydrogen storage












Space elevators



Energy storage







Hospitalities












12




approximately 142Ao










Material technology










antibacterial


nanoparticles









displays






Biomedicals




Energy storage











I Hydrogen storage




V Space elevators

VI Energy storage


VIII Hospitalities


Hydrogen storage












Space elevators



Energy storage







Hospitalities












12




approximately 142Ao










Material technology










antibacterial


nanoparticles









displays






Biomedicals




Energy storage









12




approximately 142Ao










Material technology










antibacterial


nanoparticles









displays






Biomedicals




Energy storage








Biomedicals




Energy storage





nano materials

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