seminar on cnt

8/8/2019 Seminar on Cnt

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CarbonCarbon

NanotubesNanotubesByShaweta Mutneja

M.Tech Nanotechnology

A1202810007
http://en.wikipedia.org/wiki/Image:Louie_nanotube.jpg


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What are CarbonWhat are Carbon

Nanotubes ?Nanotubes ?

Carbon nanotubes are fullerene-Carbon nanotubes are fullerene-

related structures which consist ofrelated structures which consist of

graphene cylinders closed at eithergraphene cylinders closed at eitherend with capsend with caps containing pentagonalcontaining pentagonal

ringsrings


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CapsCaps

** Typical high resolution TEM image of aTypical high resolution TEM image of ananotube capnanotube cap


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DiscoveryDiscovery

They were discovered in 1991 byThey were discovered in 1991 bythe Japanese electronthe Japanese electronmicroscopist Sumio Iijima whomicroscopist Sumio Iijima whowas studying the materialwas studying the materialdeposited on the cathode duringdeposited on the cathode duringthe arc-evaporation synthesis ofthe arc-evaporation synthesis of

fullerenes. He found that thefullerenes. He found that thecentral core of the cathodiccentral core of the cathodicdeposit contained a variety ofdeposit contained a variety ofclosed graphitic structuresclosed graphitic structuresincluding nanoparticles andincluding nanoparticles andnanotubes, of a type which hadnanotubes, of a type which hadnever previously beennever previously been

observed.observed.


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Why do Carbon Nanotubes form?

CarbonCarbon Graphite (Ambient conditions)Graphite (Ambient conditions)

spsp22 hybridization: planarhybridization: planar

Diamond (High temperature and pressure)Diamond (High temperature and pressure)

spsp33 hybridization: cubichybridization: cubic

Nanotube/Fullerene (certain growth conditions)Nanotube/Fullerene (certain growth conditions)

spsp22 + sp+ sp33 character: cylindricalcharacter: cylindrical

Finite size of graphene layer has dangling bonds. These danglingFinite size of graphene layer has dangling bonds. These dangling

bonds correspond to high energy states.bonds correspond to high energy states.

Eliminates dangling bondsEliminates dangling bonds

Nanotube formationNanotube formation ++ Total EnergyTotal Energy

Increases Strain Energy decreasesIncreases Strain Energy decreases


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Types of CNTsTypes of CNTs

Single Wall CNT (SWCNT)Single Wall CNT (SWCNT)

Multiple Wall CNT (MWCNT)Multiple Wall CNT (MWCNT)

Can be metallic or semiconductingCan be metallic or semiconductingdepending on their geometry.depending on their geometry.


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Nanotubes are formed byNanotubes are formed byrolling up a graphenerolling up a graphene

sheet into a cylinder andsheet into a cylinder and

capping each end withcapping each end with

half of a fullerenehalf of a fullerene

molecule. Shown here is amolecule. Shown here is a

(5, 5) armchair nanotube(5, 5) armchair nanotube

(top), a (9, 0) zigzag(top), a (9, 0) zigzag

nanotube (middle) and ananotube (middle) and a

(10, 5) chiral nanotube.(10, 5) chiral nanotube.

The diameter of theThe diameter of the

nanotubes depends onnanotubes depends onthe values ofthe values ofnn andand mm..


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(Definition of(Definition of

Vectors)Vectors)Chiral vector

21 aaC mnh +=a1

a2

O

(4,-5)

Ch

T

x

y

(6,3)

)23,

23(

)2

3,

2

3(

2

1

cccc

cccc

aa

aa

=

=

a

a

aacc

== 321 aa

a

a

)2

1,

2

3(

)2

1

,2

3

(

2

1

=

=

a

a


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(0,0)Ch = (10,0)

(10,0) SWNT(10,0) SWNT

(zigzag)(zigzag)

a1a2

x

y


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(0,0)Ch = (10,0)

(10,0) SWNT(10,0) SWNT

(Animation)(Animation)

a1a2

x

y


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(0,0)

Ch = (10,10)

(10,10) SWNT(10,10) SWNT

(armchair)(armchair)

a1a2

x

y
http://opt/scribd/conversion/tmp/scratch2328/wrapping.exe


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(0,0)

Ch = (10,10)

(10,10) SWNT(10,10) SWNT


a1a2

x

y


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(0,0)

Ch = (10,5)

(10,5) SWNT(10,5) SWNT

(chiral)(chiral)

a1a2

x

y


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(0,0)

Ch = (10,5)

(10,5) SWNT(10,5) SWNT


a1a2

x

y

H l L ttiH l L tti


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Hexagonal LatticeHexagonal Lattice

(n,m) nanotubes(n,m) nanotubes

a1

a2x

y

(0,0) (1,0) (2,0) (3,0)

(1,1) (2,1)

Zigzag

Armchair

(2,2)

(4,0) (5,0) (6,0)

(3,1) (4,1) (5,1)

(3,2) (4,2) (5,2)

(7,0) (8,0) (9,0)

(6,1) (7,1) (8,1)

(6,2) (7,2) (8,2)

(10,0) (11,0)

(9,1) (10,1)

(9,2) (10,2)

(3,3) (4,3) (5,3) (6,3) (7,3) (8,3) (9,3)

(4,4) (5,4) (6,4) (7,4) (8,4) (9,4)

(5,5) (6,5) (7,5) (8,5)

(6,6) (7,6) (8,6)

(7,7)

n - m = 3q (q: integer): metallic

n - m 3q (q: integer): semiconductor


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Synthesis: overviewSynthesis: overview Commonly applied techniques:Commonly applied techniques:

Chemical Vapor Deposition (CVD)Chemical Vapor Deposition (CVD)

Arc-DischargeArc-Discharge

Laser ablationLaser ablation

Techniques differ in:Techniques differ in: Type of nanotubes (SWNT / MWNT / Aligned)Type of nanotubes (SWNT / MWNT / Aligned)

Catalyst usedCatalyst used

YieldYield

PurityPurity


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Synthesis: CVDSynthesis: CVD

Gas phase deposition

Large scale possible

Relatively cheap

SWNTs / MWNTs

Aligned nanotubes

Patterned substrates

Synthesis: arcSynthesis: arc


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Synthesis: arcSynthesis: arc

dischargedischarge

MWNTs and SWNTsMWNTs and SWNTs Batch processBatch process

Relatively cheap Many side-products

Synthesis: laserSynthesis: laser


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Synthesis: laserSynthesis: laser

ablationablation Catalyst / no catalyst

MWNTs / SWNTs

Yield


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Arc dischargemethod

Chemical vapordeposition

Laser ablation(vaporization)

Connect two graphite rods toa power supply, place them

millimeters apart, and throwswitch. At 100 amps, carbonvaporizes in a hot plasma.

Place substrate in oven, heatto 600 C, and slowly add a

carbon-bearing gas such asmethane. As gasdecomposes it frees upcarbon atoms, which

recombine in the form of NTs

Blast graphite with intenselaser pulses; use the laser

pulses rather than electricityto generate carbon gas fromwhich the NTs form; try

various conditions until hiton one that producesprodigious amounts of

SWNTs

Can produce SWNT andMWNTs with few structural

defects

Easiest to scale to industrialproduction; long length

Primarily SWNTs, with alarge diameter range that

can be controlled by varyingthe reaction temperature

Tubes tend to be short withrandom sizes and directions

NTs are usually MWNTs andoften riddled with defects

By far the most costly,because requires expensive

lasers

Overview of potentialOverview of potential


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Overview of potentialOverview of potentialapplicationsapplications

< Energy storage:

Li-intercalation

Hydrogen storage

Supercaps

> FED devices:

Displays

< AFM Tip

> Molecular electronics

Transistor

< Others

Composites

Biomedical

Catalyst support

Conductive materials

???

Overview of potentialOverview of potential


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Overview of potentialOverview of potentialapplicationsapplications

< Energy storage:

Li-intercalation

Hydrogen storage

Supercaps

> FED devices:

Displays

< AFM Tip

> Molecular electronics

Transistor

< Others

Composites

Biomedical

Catalyst support

Conductive materials

???


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Energy StorageEnergy Storage

Experiments & ModellingExperiments & Modelling

Electrochemical Storage of LithiumElectrochemical Storage of Lithium

Electrochemical Storage of HydrogenElectrochemical Storage of Hydrogen Gas Phase Intercalation of HydrogenGas Phase Intercalation of Hydrogen

SupercapacitorsSupercapacitors


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Energy StorageEnergy Storage

3-electrode cell3-electrode cell- + -

2

reduction

oxidationCNT H O e CNT H OH x x x x+ + + +

( ) + -2

reduction

oxidation Ni OH NiOOH H e + +

Work Electrode

Counter Electrode

Lithi El t h i lLithium Electrochemical


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Lithium ElectrochemicalLithium Electrochemical

ModelModel

i hi lLithi El t


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Equilibrium saturation

composition for graphite:LiC6

Purified SWNT bundles:

Li1.7 C6

Ball-milled SWNTs:

Li2.7 C6

20 min

10 min

0 min

Lithium ElectroLithium Electro

ChemicalChemical

Li hi ElLithi El t


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Lithium ElectroLithium Electro

ChemicalChemical

EtchingTwo types: lengths of 4 and

0.5 mGood Crev (Li2.1 C6)

Smaller hysteresis

Cut SWNTs have betterproperties concerning Li

intercalation

Voltag

e

[V]

y rogeny rogen


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y rogeny rogenElectrochemicalElectrochemical

Lennard Jones PotentialLennard Jones Potential

( )12 6

H-H H-H

LJ H-H4U r

r r

=

y rogeny rogen


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storage modelstorage model

Model of Hydrogen Storage at

room temperature for different

diameters of SWNTs

y rogeny rogen


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Charging & DischargingCharging & DischargingCharge Discharge Cycle

H dH d


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HydrogenHydrogen

ElectrochemicalElectrochemical Many contrasting conclusions:Many contrasting conclusions: Positive Ranging from: 0.4 2.3 wt% HPositive Ranging from: 0.4 2.3 wt% H

Negative: No systematic relationshipNegative: No systematic relationship

between purity and storagebetween purity and storage storagestoragenot due to SWNTsnot due to SWNTs

More investigations on theMore investigations on the

mechanism of storage are needed inmechanism of storage are needed inorder to explain this wide range oforder to explain this wide range of

resultsresults

G Ph I t l tiG Ph I t l ti


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Gas Phase IntercalationGas Phase Intercalation

of Hydrogen modelof Hydrogen model

G Ph I t l tiG Ph I t l ti


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Gas Phase IntercalationGas Phase Intercalation

of Hydrogenof Hydrogen Contrast in results is very high: rangeContrast in results is very high: range

from 0-67 wt%from 0-67 wt%

Reasonable range: 2-10 wt%Reasonable range: 2-10 wt%

More modelling neededMore modelling needed

To compare models they have to useTo compare models they have to use

the same parametersthe same parameters


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Super CapacitorSuper Capacitor

Electrochemical double layer

E l e c t r o d e ( + )E l e c t r o d e ( - )

S e p a r a t o r


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Molecular electronicsMolecular electronics

FEDsFEDs

CNTFETs

SETs


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Field Emitting DevicesField Emitting Devices

Single Emitter

Film Emitter


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Single Emitter

Film Emitter


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Single Emitter

Film Emitter

Patterned Film FieldPatterned Film Field


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Patterned Film FieldPatterned Film Field

EmittersEmitters

Etching andlithographyConventional CVD

Soft lithography

T i t P i i l iT i t P i i l i


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Transistor Principle inTransistor Principle in

CNTFETsCNTFETs

Transistor

CNTFET


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Doping of CNTsDoping of CNTs

SingleSingle ElectronElectron


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SingleSingle ElectronElectrontransistortransistor


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Future Uses of CNTsFuture Uses of CNTs

Nano-ElectronicsNano-Electronics Nanotubes can be conducting orNanotubes can be conducting or

insulating depending on their propertiesinsulating depending on their properties

Diameter, length, chirality/twist,Diameter, length, chirality/twist,

and number of wallsand number of wallsJoining multiple nanotubes together toJoining multiple nanotubes together to

make nanoscale diodesmake nanoscale diodes Max Current Density: 10^13 A/cm^2Max Current Density: 10^13 A/cm^2


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The Space Elevator

The Idea To create a tether from earth to some object

in a geosynchronous orbit. Objects can then

crawl up the tether into space. Saves time and money

The Problem 62,000-miles (100,000-kilometers)

20+ tons


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Pictures from

http://www.space.com/businesstechnology/technology/space_elevator_020327-1.html

The Space Elevator
http://www.space.com/businesstechnology/technology/space_elevator_020327-1.htmlhttp://www.space.com/businesstechnology/technology/space_elevator_020327-1.html


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The Space ElevatorThe Space Elevator

The Solution: Carbon NanotubesThe Solution: Carbon Nanotubes 10x the tensile strengh (30GPa)10x the tensile strengh (30GPa)

1 atm = 101.325kPA1 atm = 101.325kPA

10-30% fracture strain10-30% fracture strain

Further ObstaclesFurther Obstacles Production of NanofibersProduction of Nanofibers

Record length 4cmRecord length 4cm Investment Capital: $10 billionInvestment Capital: $10 billion

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