Fundmental and Application of Nano Material

8/12/2019 Fundmental and Application of Nano Material

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By : Noha Mohamed

Abd El Twab

Cairo University

Faculty Of Engineer

Post Graduated

Mechanical Design And Production


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PARTI

FUNDAMENTALSOFNANOMATERIALS

SCIENCE

CHAPTER1Quantum Mechanics and Atomic Structure


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PHOTOELECTRICEFFECT

cathode illuminated by light, ammeter record current I

Below threshold frequency ( Vo )no current depend on material

of cathode metal.

current directly proportional to intensity of light.

K.E of electrons, not related to intensity but frequency of light.

Increasing intensity of light increase the saturation current.

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EINSTEINSEXPLANATION

This contradict Maxwell wave theory

Assumed light is particles he called light quantaphotons.

energy of photon expressed as

photoelectric is interaction between incident photons and

electrons inside metals.

Work function m energy required to emit a bond electron isproperty to cathode metal

K.E of electron = -exStoppingvoltage(Vo) =

Energy of light - Metal work function

=hvhvo

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Duality of Light

Light has both characteristic of wave and particle

DUALITYOFELECTRONS Broglie :all matter had wave/particleduality.

relation between momentum (particle), andwavelength, (wave).

Youngs double-slit exper. electron beam show

interference and diffraction

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TIMEINDEPENDENTSCHRODINGEREQU.

Proposed equation analogous to harmonic wave

1-D =h/2

m:electron mass

V electronpotential energy

wave format of electron.

Born proposedprobability finding electron at locationx

and time t as.

Based on assumption obey following rules:1. has to be continuous and smooth in the space.

2. the probability, so it has to be a real number.6


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ELECTRONSINPOTENTIALWELL

1D infinite potential V (x )

Out potential probability finding

electron zero.

In potential well electron like free

electron

Using boundary conditions.

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electron energy in potential well be at finite

discrete levels

difference between 2 adjacent energy levelsbe

If a is large enough energy level not consider

discrete but continuous

Quantum mechanics produces the same

results as classical mechanics.

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THEHYDROGENATOM

wave function expressed in

quantum numbers:

principle quantum number n

orbital angular momentum quantum number l magnetic quantum number ml

in hydrogen n, l, and ml related to each other

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Level energy, function of n for hydrogen atoms

for the ground state, n = 1, l = 0, and ml = 0,

next energy level,several available states:- n = 2, l = 0, ml = 0 -n = 2, l = 1, ml = 0

-n = 2, l = 1, ml = 1 - n = 2, l = 1, ml = 1

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THEPERIODICTABLE l = 0,1, 2, 3, they called s (sharp), p (principle), d (diffuse),

and f (fundamental).

Energy level of 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < . . . .

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periodic table built based on three principles:

lowest energy rule: electrons fill up from bottom (lowest

energy) to top.

Pauli exclusion principle: Electrons cant share the same

exact quantum states.

Any combination of n, l, ml hold pair of electrons, one spin upand one spin down.

Hundsrule: electrons in same n and l orbitals wouldprefer their spins to be parallel

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CHAPTER2Bonding and Band Structure


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CLASSICATOMICBONDING

bonding seeks to balance

Coulomb force proportional to 1/r @ro repultion force=attraction force stable

bond length

Eo bond strength

LCAO THEORY

when atoms form molecule, electrons fromatoms occupying molecular orbitals expressed

as

linear combination of atomic orbitals 14


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:wave function of atom i in n-atom molecule

Ci : atomic contribution to molecular orbitals

Get contribution of each atom Huckel assumed:

1. coulomb integrals equal (ionization energy)

2. Bonding only between neighbor atoms. Resonance integral nonzero

3. wave functions of atoms orthogonal, overlap integrals zero

Molecular orbital wavefunction

HMO (Huckel molecular

orbitals).

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EXAMPLE: TWO-ATOMMOLECULEH2

coulomb integral H atom=ionization energy= 13.6 eV

overlap integral 2 adjacent H =bonding energy 1 eV

2 molecular orbitals:

1. bonding molecular orbital

2. antibonding molecular orbital

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bonding molecular orbital has lower energy. So electrons

occupy this state

The bonding energy : difference before and after the

molecule is formed, in this case

Need to provide amount of additional energy to either

ionize the atom or break bond in molecule 17


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Ring

Bonding formed betweenatoms 12 ,23 and 31

ring structure energyfavorable for a three-atom

molecule

THREE-ATOMMOLECULE

Chain

Bonding formed between

atoms 12 and23

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MANY-ATOMMOLECULE

# molecular orbital energy levels is = # atoms in the

molecule.

energy levels systematically distributed below and above

All valence electrons occupy energy states below

when # energy levels gap between adjacent energy

levels becomes consider continuous energy spectrum

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A O C BO G C S SO S B


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ATOMICBONDINGINCRYSTALLINESOLIDS: BAND

THEORY

Energy Band in Solids

N atoms in solid provide N orbitals between&

N large, energy levels no longer discrete

energy level overlap to energy bands Betweenbands forbidden gap no energy level exists.

highest energy band occupied by electrons calledvalence band (VB)

If VB fully occupied,next energy band called conduction

band (CB).

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PARTIALLYFILLEDENERGYBANDFORMETALS

Li fully 1s orbital and partially 2s orbital

Solid lattice 2s level electron split to N level N levels between & consider

continuous band

N orbitals can contain up to 2N electrons

Li provide N electrons sohalf-filled 2s band

formed

Left V0 Apply electron energy on left raised of eV0 .

band partially filled empty orbitals available electrons onleft have higher energy electrons move from left to right topass a current.

This is why Li is conductive 21


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ENERGYBANDFORINSULATORSAND

SEMICONDUCTORS

IVA group has 4 valence electrons in outer shell carbon and silicon belong to IVA

For a C

2s & 2p close energy over lap

4 orbitals distributed, it forms a tetrahedral structure withall four neighboring called diamond structureby covalentbond bonding and anti bonding form .

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BONDINGANDBANDSTRUCTURESINNANOCRYSTAL

MATERIALS

Macroscopic crystalline solid 10exp(23)atoms

Nanocrystal 100 to 10,000 atom

Molecules 2 to 10 atoms

2 Method to study1. Button up method: Expand single molecule calculation (LCAO)

to nanocrystal ,Need high computing power (useful up to 1000

atoms)

2. Top-down method: adds size-dependent unique properties ontop of the standard band structure of macroscopic crystalline

materials.

This method is very useful for quantum well and other thin-film

structures. 23


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TOP-DOWNMETHODFORQUANTUMWELLS

ANDDOTS Quantum wells & quantum dots examples for method.

Quantum wells : potential wells confine electron motion to2D planar instead 3D in free electron

semiconductor layer of small energy gap between 2

semiconductor layer with larger energy gaps

Thickness 10A to 100A comparable to de Brogliewavelength so levels inside well discrete.

Example:

quantum well layer band gap 2.5 eV, To Calculate the

ground state in quantum well of 10A

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QUANTUMDOT

Nanocrystal embedded in wide bandgap insulator.

Ground state energy 3times that of quantum well quantumization of energy is more significant has

narrower spectrum .

Quantum dots used for light emitting diodes (LEDs),

lasers, solar cells, optical devices, and displays.

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BOTTOM-UPMETHODFORCARBON-BASED

NANOCRYSTALS

Used on nanocrystal structures, as CNTs and the

fullerene ball

DIAMOND: 3D CARBON-BASEDSTRUCTURE

form sp3 hybrid orbitals and covalent bonding with

its 4 neighbors in a tetrahedral structure.

strong covalent bonding, diamond is hard

and not easily deformed because of large bandgap it is electric insulator but

& crystal clear (no visible light absorbed)

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GRAPHITE: 2D CARBON-BASEDSTRUCTURE

sp2hybridizecarbon atom form plane covalentbond with 3 neighbors (120) and hexagonal

network

Reminder electron form pi bond

band electron touch each other

no energy gab

graphite is conductor in direction perpendicular to

plane Pi is weak bond ,graphite has anisotropic mechanical

properties

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CARBON NANOTUBE


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CARBONNANOTUBE

rolled-up form of 1-atomic-layerthick graphite, called 2D

graphene sheet.

CNT classify by chiral vector (n, m)

Ch impact out-of-plane bonding and band structure.

if metallic n-m multiple of 3. m = 0 zigzag,

n = m armchair. Conductor

Band structure also function

of raduis

As radius dec it be metallic28


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C60 FULLERENEBALL

consists of 20 hexagons and 12 pentagons.

2 kinds of bonding, between pentagons andhexagons and between two hexagons

CC single bonds and C=C double bonds

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CHAPTER3Surface Science for Nanomaterials


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CRYSTALSTRUCTUREANDCRYSTALLOGRAPHY

CRYSTALSTRUCTURES

crystalline materials considered repeating pattern ofpoints in called a lattice.

Classified into7 crystal systems&14 brave lattice 3 most

common in pure metal FCC , BCC,& HCP

a or c called lattice constant

Crystallography : systematic method for specify planes

and directions in crystal structure31


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COORDINATESYSTEM. Directions 3 noncoplanar axes along edges (a, b, c) with

origin at corner

Unit cell edges not same length and not so coordinatenot Cartesian unless in cubic (FCC,BCC)

[uvw] integers indicate steps from origin

family of directions identical due to symmetry

plane // or intercept one of 3 axes.

Reciprocal of interceptions on 3axes(hkl)Miller indexindex orientation of plane.

plane // to axes interception infinite reciprocal is 0

{hkl } to index a family of crystal planes 32

CLOSE-PACKED DIRECTIONS PLANES AND


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CLOSE-PACKEDDIRECTIONS, PLANES, AND

STRUCTURES

assume atoms are solid balls with the same radius r

BCC Structures Diagonal or close-packed direction all atoms touch

other

relationship between r and a

close-packed plane {110}

volume packing density(atomic packing factor or APF) BCC have 8 atoms @ corner shared by 8 neighbor cubes and

1 atom @ center.

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CLOSE-PACKEDSTRUCTURES

It can be proven mathematically that max. packing

density is 12 atoms

APF and packing density of HCP equal of FCC

Both HCP and FCC are closed packed structure but

with different stacking sequence.

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SURFACEENERGY

Atoms in surface has fewer neighbors compared with

bulk atom It has unsaturated bonds that added extra energy

Total surface energy 1/R

of 1micro sphere =1000 of 1nm v.significant at nano scale surface energy / uint area

Total surface energy E=x S ;s:surface area

Nature aim to decrease extra energy by 2 ways :

Min surface energy / unite surface by :

Use surface plane that have low surface energy

Altering local surface atomic geometry (reconfigration )

Reduce S 35


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CRYSTALLOGRAPHICALLYPREFERREDSURFACE Closed packed plane highest neighbors fewest unsaturated bond

BUT it may not have min. since has more atoms per unit area

WULFFCONSTRUCTIONSANDEQUILIBRIUMSHAPEFORNANOPARTICLES

inc as inc.Edge atom has 2 broken bondsparticle size dec. edge atoms be v. significant

WULFFCONSTRUCTIONSpolar

representation of used to predict

equilibrium shape of single-crystal

particles, especially nanoparticles.

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SURFACERECONFIGURATIONS1-HOMGENOUS RELAXATIONANDRECONSTRUCTIONS Surface atoms assume different positions to bulk to relax surface

energy.

Surface relaxation atoms in surface shift relative to layer underneath, while their position

within surface layer unchanged

This difference in

interatomic distancediminish in 3rdor 5thlayer

Surface reconstructions

Lead to Change in surface structure and symmetry

2 Si atoms reunite with 2dangling bonds. #of dangling

bonds dec.by 2,lower surface

energy. 2 1 symmetry

symmetry

of 2 2

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2-HETROGENEOUSADSORPTION Take place when 2ndmedium exist air vapor .. Etc

adsorption layers have own unit cell & symmetry

ADSORPTIONSITES1-ON-TOPSINGLEBONDWITHBELOWATOM

2-BRIDGINGSITE

BONDWITH2ATOMS

3-HOLLOWSITE

FORMMOREBONDSPHYSICALANDCHEMICALADSORPTION

Depending on bond nature, adsorption divided into physical (van der

Waals bonding) and chemical adsorption(covalent bonding).

Chemical adsorption Physical adsorbtion

Temp. of process molecules type condensation point of gas

Adsorption enthalpy ch. Bond strength (40/80KJ) molecule mass &polarity (5/40KJ)

Saturation Limited monolayer Multilayer38


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SURFACEAREA&SURFACETHERMODYNAMICS Min. surface energy throuh exposing less surface

area

Surface area in nanomaterial in CNT unpaired electron form pi bond inside tube tominimize surface energy

Half buckeye ball (C60) on tip of tube

Thermo dynamic equilibrium state Nanosphere of radius r thermodynamically

equilibrium ifr > r*

Gets from overall Gibbs free energy change

To push critical size r* smaller, dec. for nanoparticle ( ) or inc. Gibbsfree energy per unit volume (Gv ).

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WETTING


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WETTINGphenomenon use in nanomaterial fabricationscombine of dec. surface area and to min. overall energy

YOUNGSEQUATIONANDCONTACTANGLES

Liquid drop on solid surfacewetting angle characteristic value to evaluate how wellthe liquid spreads on substrate surface in vapor environment.

COMPLETEANDPARTIALWETTING2nd phase spread on substratecomplete wetting

> Have 2 interfaces (S-L , L-V) to min surface energy ,ideal case forpainting, coating, and depositing films in nanomaterial fabrications

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CHAPTER4Nanomaterials Characterization


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X-RAYDIFFRACTIONANDLAUELAWAdd 2wave of same amplitude and frequancy

In phase constructive diffraction

180 phase diff. destructive diffraction LAUE Method

if wave length of X-ray similar to lattice parameters itpossible to diffract X-ray through crystal lattice.

Braggs Law

beam 2 has to travel extra distanceMO2 + MO2 = 2d sin

To be in phase 2d sin =n

n = 1,2,3.. d = lattice parameter

Knowing & get d 42

ELECTRON MICROSCOPY FOR NANOMATERIAL


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ELECTRONMICROSCOPYFORNANOMATERIAL Electron accelerate under high voltage to get small to

provide high resolution at nanoscale

Interaction Between Electron Beams and SolidsAccording to the properties and directions signals transmitted can be dividedinto the categories1-Transmitted Electrons

Scattered elastically or not ch. Properties determine

by energy loss

2-backscattered electronElectrons adsorbed & scattered and then escaped

determine crystal orientation

3-secondary electrons when electron

surface excite electrons use to determine ch. Comp.

4-x-rays

Electron in inner shell also excited , electron in outerfill inner shell delta energy is x-ray characteristic ch.

Composition

5-Auger electrons

X-rays excite other electrons use to determine ch.

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TRANSMISSION ELECTRON MICROSCOPE (TEM)


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TRANSMISSIONELECTRONMICROSCOPE(TEM)

Consist of electron gun, magnetic lens chamberand screen

Revealing phase/crystallographic orientationusing diffraction and ch. Comp. use energyspectrum

Resolution up to 0.5A

Example :SWCNTs

Diffraction pattern can determine diameter andchiral angle

Energy spectrum give inf. About ch. Comp. bondand dielectric properties

Situ TEM can record process as phase

transformation deformation or film growth Example :

heat sample then cool directly &recored phasedeformation

Run tesile test or indentation44


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SCANNINGELECTRONMICROSCOPE(SEM)

Scan electron beam across sample

surface & collect scattered electron forimaging

Image formed use back scattered signals

beam energy not need to be high sample not need to be transparent

only need to be conductive

resolution up to 1 to 5 nm

Reveal inf. About surface topography Backscattered electrons related to atomic

nu. (z)45

S P M (SPM)


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SCANNINGPROBEMICROSCOPE(SPM)

probe of fine tip scan surface

Atomic level

Two types Depending on signals collected:

1. atomic force microscope(AFM) atomic force recorded

cantilever and piezo material

2.

scanning tunneling microscope (STM), record tunnelingcurrent between probe tip and surface to reconstruct

surface information

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SURFACE ANALYSIS METHODS


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SURFACEANALYSISMETHODS To descover ch. Comp. bonding&band structure

1-Auger electron spectroscopy AES

Plot electron bean intensity vs K.E of electronif beam kicks electron K shell, then electron L

shell falls in K shell emitted EK EL .releaseAuger electrons EA. So K.E detector record E =EK EL EA 3 energies element specific use for surface ch.

Comp. analysis.

2- X-Ray Photoelectron Spectroscope (XPS)

Related to binding energy

If x-ray energy = Ei & K.E of electron Epbinding energy Eb= Ei-Ep

obtain binding energy inf. and subsequentbonding/ electronic band 47


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PARTII

NANOMATERIALSFABRICATION

CHAPTER5Thin-Film Deposition: Top-Down Approach

THIN-FILM DEPOSITION


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THIN-FILMDEPOSITION Fabricate 2 to 3 larger in 1 or 2 dimens. than desired then nano-

patterning technique to get small feature

HOMOGENEOUSFILMGROWTHMECHANISMS System stable equilibrium between thermodynamics and kinetics to 2

mechanisms takes place

1-STEPPROPAGATION Terrace island 4side extra surface Steps 2 side extra surface Kinks no extra surface, less overall surface, stable

Steps and kinks probability small, need high temp.& fastdiffusion

2-ISLANDGROWTH Terrace forming cluster to min. surface energy

Cluster less mobile ,stable &attract more atoms

takes place @low Temp. low surface diffusion

&deposition rate

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H OG O S F G O M C S S


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HETEROGENEOUSFILMGROWTHMECHANISMS

Deposited on substrate of differ materials& structures

Total energy include surface energy & elastic energy due to latticemismatch

Classify into 3 category

1-Frankvan der Merwe ModelIf Lattice parameter film match substrate elastic energy negligible

To form continuous film wet criteria must satisfy

Surface energy of substrate >surface energy of film +interface energy

2- VolmerWeber ModelWetting doesnt satisfy ;it grown into 2D island but assume perffect lattice

match

3- StranskiKrastanov ModelThere mismatch

Model based on competition between surface energy &elastic strainenergy 50

THIN-FILM DEPOSITION METHODS


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THIN FILMDEPOSITIONMETHODS

PHYSICALVAPORDEPOSITION(PVD)Substrate heated or biased film (source of energy)vapor

condensationon substrate

Process happen in high vacuum

PVD sub divide according source of energy

THERMALEVAPORATION Equipment sample ,High deposition rate large substrate size but limited

material (need low evaporation Temp.)

SPUTTERING Moment transfer high energy ions bombard

target surface transfer K.E > chemical bond energy

Material sputter &deposit on substrate

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C V D (CVD)


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CHEMICALVAPORDEPOSITION(CVD) Involve chemical reaction

1-mass transportation of reactants gas/liquid

2-adsorption of reactants

3- chemical reaction on substrate surface

4- desorption of by-products of chemical reaction

5- pumping away by-products and unreacted reactant.

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CHAPTER6Nanolithography: Top-Down Approach

NANOLITHOGRAPHY


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NANOLITHOGRAPHY

Divide based on patterning strategy into

1-parallel replication 2-serial writing

Parallel replication useful for patterns predefined by serialwriting

PHOTOLITHOGRAPHY

use light shining through masked area on photoresist coatedsubstrate

substrate then etched in plasma or

solvent ,remove certain areas and

make patterns on substrate

Limitation

size of pattern must up to thewavelength of t light(37 nm)

process done only on flat surface55

NANOIMPRINT LITHOGRAPHY (NIL)


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NANOIMPRINTLITHOGRAPHY(NIL)

high-throughput, high-resolution

replicate by mechanical contact & 3D material

displacement

NIL Process

resist can be thermal plastic or

UV curable polymer (UV-NIL)

or other deformable material

Air Cushion Press

RIE reactive

ion etching

to reduce mold damage and prolong its lifetime, avoid

high-pressure, relative rotation and lateral shiftingbetween the mold and substrate

air cushion press (ACP) developed utilizes a gas (or fluid) to press the

mold and substrate against each other in a chamber56

SERIALWRITING


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AFM LITHOGRAPHY

writing using sharp probe tips with an atomic force

microscope (AFM).Advantages: simple, fine size (10nmlevel),high resolution

accuracy and speed

SCRATCHINGANDNANOINDENTATION

AFM use for nanoscale material removal

Mechanical: direct tip scratch ,plowing

Chemical :tip-induced electrochemical etching.

Limitation :tip forces cant be large to possible damage

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NANOGRAFTING


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NANOGRAFTING

a nanoscale patch of a thiol-on-gold SAM is exchanged

with a different thiol by the action of an AFM tip operated in

contact mode at high load

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TEMPLATEDSELF-ASSEMBLYOFBLOCK


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COPOLYMERS combining bottom-up self-assembly with top-down patterned templates,

templated self-assembly (TSA) can provide

TSA are not required to be crystalline materials

topography or chemical pattern of top templates guide organization of

component materials.

LS ranges from the characteristic length scale, Lomuch larger than Lo

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CHAPTER7Synthesis of Nanoparticles and TheirSelf-Assembly: Bottom-Up Approach

NANOPARTICLESNPS


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Less than 10nm at least 1D

Unique properties ,large surface area ,quantum effect and surfaceplasmon resonance

SYNTHESISOFNANOPARTICLES1-COPRECIPITATION NPs made by precipitation of solids from aqueoussol. Then thermal

decomposition of those precipitates

Steps : nucleation, growth, coarsening and agglomeration

Complex, particle morphology sensitive to conditions butenvironmentally friendly

NiO, ZnO precipitated from metal chloride gives amorphous product;subsequent annealing to give NPs crystalline

reaction rate plays a key role

slow growth :NPs follow Oswald ripening process

rapid growth: irregular morphology and scattered size distribute61

Oswald ripening process


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Small particles vanish while large particles grow in size.

Surface Molecules less stable than well ordered and packed in the interior.

Large particle has lower surface-to- volume ratio

system lower its energy, surface molecules of small particle diffuse and addto surface of larger

Nonaqueous use of an organic solvent

Can Create inorganic semiconductor NPs (metal oxide) with controlmorphologies and size distributions

Not sensitive for condition but toxic and require long time (days)

Example :CdSe NPs shapes explained on basis of model and selectiveadsorption of surfactants on different crystallographic faces

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2-SOL-GELPROCESS


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hydrolysis and condensation of liquid precursor to solid

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Finding suitable precursor andsolvent is the key

Aqueous and Nonaqueoussolvent is used

Hydrolysis controlled by wateramount in nonaqueous and PH

in aqueous

Surfactants and coordinating

solvent use as satbilizing toresist agglomeration

TiO2 nanorods produced bythis method

3-MICROEMULSIONS


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1943, Hoar and Schulman reported

combinations of water, oil, surfactant & alcohol or

produce clear and homogeneous solutions

surfactant(hydrophilic head & hydrophobic tail) in

mixture of water & oil form spherical aggregates ,

which polar ends of surfactant molecules orienttoward the center

self-assemble nanostructure can

form spherical and cylindrical

Types :

Direct (oil in water)

Reverse (water in oil) 64

4-HYDROTHERMAL/SOLVOTHERMALMETHODS


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In sealed vessel, brought solvent above boiling point.

Where Chemical reactions taking

Above critical point solvothermal be supercritical processwhere happen change in density

Supercritical fluid (SCFs) has

characteristics of both liquid and gas

Ch. Compounds easily desolve in SCFs

Low surface tension low viscosity and high diffusivity

nanoscale materials demonstrated in supercritical water

(SCW).

metal nitrates used as precursors to prepare a wide variety

of metal oxides

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5-TEMPLATED SYNTHESIS


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5 TEMPLATEDSYNTHESIS Mesoporous materials of uniform pore size use as template for

synthesizing nanoparticles ,use as nanoreactors

2 methods to load semiconductor NPs into pores of amesoporous material:

1-in situ:mix NPs precursors with micelles before formation ofmesopores

2- post-treatment: grafting NPs onto pore surfaces of an as-preparedmesoporous material

6- NPSOFORGANICSEMICONDUCTORS organic NPs easy to synthesize and mechanically flexible

Reprecipitation method: dilute solution of starting material in

water soluble media injected stirred water causes the solutesto be precipitated in the form of nanocrystals

Organic semiconducting NPs of monomers (single molecules),oligomers (monomers linked to form a short chain), andpolymers (monomers linked with a long chain) are all revealed.

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SELF-ASSEMBLYOFNANOPARTICLES


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for creating functional devices for nanoelectronics and

sensors

noncovalent interactions dictate self-assembly include hydrogen bonding

dipoledipole

Electrostatic

van der Waals hydrophobic interactions

1- HYDROGENBONDING-BASEDASSEMBLY

surfactants coat NPs surface

provide hindrance between neighboring NPs make NPs able to form hydrogen bonds between terminal

NPs consider bricks& ligands are mortar

example of surfactant is dendrimer.67

2-ELECTROSTATICASSEMBLY


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Electrostatic interaction simple way to create organize layer-by-layer (LbL) assembly of nanostructures

based on the alternating adsorption of oppositely charged

materials Potential applications in areas as:

surface modification

electrochemical devices

chemical sensors

nanomechanical sensor

Lead to freestanding structures not full contact with a solidsubstrate to sustain their shapes

Prepare:

LbL microcapsules microtubules,

Microcubes

Microcantilevers

Fabricate NPNP composite nanostructure array68

3-SHAPE-SELECTIVEASSEMBLY


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NPs prepared as tetrahedraloctahedral and cubic

Due to polarity difference betweenfaces of particles dipole momentsgenerated within NPs

Nanocubes

with dipoles form wires

with dipoles form sheets

4-HYDROPHOBICASSEMBLY hydrophobic effect driven to

assemble into larger structures

assemble silver nanocubes intohighly ordered superlattices, throughselective face with hydrophobicligands 69

5-TEMPLATE-ASSISTEDASSEMBLYt l t id l tf t i ti l


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templates provide platform to organize particles

through covalent and noncovalent interactions

NPs can assemble at interior or exterior oftemplate

ice use as template to prepare NP fibre

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COLLECTIVEPROPERTIESOFSELF-


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ASSEMBLEDNANOPARTICLES

These self-assembled NPs display collective properties

different from the isolated particles and bulk phases

NPs organized in 2D superlattices has collective optical

and magnetic properties can be observed as a result of

the dipolar interactions

For example:optical properties of self-organized NPs

give rise to several plasmon resonance modes

Np organized 3D superlattices a new generation of

materials.

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PARTIII

NANOMATERIALSPROPERTIESAND

APPLICATIONS

CHAPTER8Nanoelectronic Materials

NANOELECTRONICMATERIALS


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today, we are able to pack more than 1.9 billiontransistors into one chip compared with 60

transistors in the same area 40 years agoSINGLE-ELECTRONTRANSISTORS(SETS)

device control the motion of a single electron withquantum dots and a tunnel junction

it is based on nanomaterials science and thequantum effect

to understand the fundamental principles of SETs, weneed to start with a single-electron capacitor (SEC),

which is the simplest known single-electron device.Also called a single-electron box 73

SINGLE-ELECTRONCAPACITOR


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consists of a quantum dot located between 2

electrodes

Closer source tunnel junction

other electrode control gate capacitor

apply voltage electron injected

into or fromquantum dots depend on sign

because of size of quantum dots every

injected electron into quantum dots need

excessive energy due to Coulomb blockadeeffect

This unique property enables to control motion of

single electron through tunnel junctions74

SINGLE-ELECTRONCAPACITOR


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voltage zero no electron tunnel quantum dot charge zero

voltage increase electron attract to quantum dot

Take antherexcessiveenergy > Coulomb blockade energynew electron emit

Plot relation between net charge in quantum dot and gate

voltage is step function

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OPERATINGPRINCIPLESFORSETS


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SET 3-terminal device source , drain & gate electrode

with quantum dot in middle of source and drain

Source grounded and voltage apply on

gate (Vg) & drain electrode (Vd)

Vg=0 no electron emit

Vg>=Vt (threshold voltage) electron

tunnel through source & eject into drain

forming current

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CARBON NANOTUBE BASED NANOELECTRONIC DEVIC


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CARBONNANOTUBE-BASEDNANOELECTRONICDEVICINTRODUCTIONTOCNTS

Carbon has 4 electron in outer shell Can form sp3 hybridization

as in diamond or sp2 hybridization as graphite and graphene

BANDSTRUCTUREOFGRAPHENEANDGRAPHITE

Relation between energy state E and wave vector Ky & Kx

&* touching each other in 6 Corner

Other location separated

by band gabs

@ specific Temp. band gap become

zero and graphene called gapless

semiconductor

A set of planes stacked electronelectron

interaction Then graphite is metallic and conductive 77

BANDSTRUCTUREOFCNT


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axial direction along tube axis considered infinite

Radius direction has periodicity defined by chiral vectors

Ch

periodic boundary condition of CNTs determine that only

discrete set of the (kx , ky ) state is allowed

The armchair CNT is gapless semiconductor

But due to small dim.

Electron interact with

each other and be

Conducting For general; CNTs are

Semiconductor because of exist band gabes78

FABRICATIONOFCNTS


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PVD METHODS physical vapor deposition where momentum transfer sputters

off target First PVD methods called electric-arc discharge

2 graphite electrodes placed close to each other insidechamber full of inert gas voltage applied across two electrodes

electric arc discharge occurs between electrodes

heating the electrode locally up to thousands of degrees

evaporating the carbon atoms from electrode

carbon atoms recrystallize at the end of the negative electrode

forming a multiwall CNT (MWCNT) Easy ,cheap but difficult to control

Radius from 4 to 40 nm

Transition metal use as catalyst to produce SWCNT79

CVD METHODS


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vaporliquidsolid (VLS) root growth Hydrocarbon disassociate at metal surface into H and C

dissolve into transition metals carbon supersaturated inside metal

precipitate out in form of a curved-up graphene sheet

leads to a fullerene cup.

more hydrocarbons disassociate at surface and precipitates forming elongated carbon nanotubes

provide better control on CNT growth

transition metal as Co or Ni needed

Use hydrocarbon CnHm as methane 80


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CHAPTER9Nano Biomaterials


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NANOBIOMATERIALS

Biology adds sophisticated nanomachines operating byentirely classical molecular mechanisms

Nature source of inspiration to the fabrication biological

components with structures having incredible functions

DNA illustrates features of self-assembly predictablestructure develop systems simulate behavior

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CHAPTER10Nanostructural Materials

NANOGRAIN-SIZEDSTRUCTURALMATERIALS


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thermal and thermal mechanical processing use to refine

grain size down to nanograin-sized structural materials

Why Grain Refinement?

materials strength and toughness have inverse relation

Grain refinement useful for both

Hall-Petch equation

y:yield strength d:grain size

i:internal friction Ky:Hall Petch slop

fracture strength f derived from dislocation &Griffith

theory for brittle crack

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NANOGRAIN-SIZED STRUCTURAL MATERIALS


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i proportional to Temp

f slightly change with temp. resulting ductile-brittletransition

At y= f at temp. equal Tc (Transition Temp.)

C,B,constant

grain refinement only mean to

yield strength inc.

apparent fracture strength inc.

transition temperature lowered 85

NANOGRAIN SIZEDSTRUCTURALMATERIALS

GENERALAPPROACHESFORGRAINREFINEMENT


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ferritic steel cleaves along the {100} planes.

effective grain size

defined as coherent length on crystallographic cleavage planes, Or mean free path of crack propagation along the {100} planes in

BCC ferritic steel

plastic deformation is dislocations glide along {110} planes

Example :lath martensitic steel

grains subdivide into packets of thin

close martensitic laths

structure within packet V.fine 100nm

laths within packet close crystallographic order and

lath boundaries only low-angle boundaries

Packet size define effective grain size

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Fracture cleavage follow {100} plan


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Fracture cleavage follow {100} plan

2 ways accomplish grain refinement:

Thermal mechanical

Thermal processing

THERMALMECHANICAL PROCESSING

combination of mechanical work to obtain large amount ofplastic deformation and thermal exposure to induce

recrystallization

Disadvantage:

difficult achieve large amount of uniform plastic deformationto produce ultrafine grain size through thickness of plate steel

espical in high strength , high alloy thick plate87

THERMALPROCESSING applicable to high strength thick plates bars


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applicable to high-strength thick plates, bars

cyclic thermal treatment change properties of martensitictransformation and produce ultrafine grain size in lath

martensitic steel Ex:During diffusionless martensitic transformation steel Show

coherent crystallographic relationship with parent phase

under certain thermal process conditions

Crystallographically cleavage planes {001} show large anglemisorientation

Where dislocation slip planes {011} small angle orientationbetween adjacent martensitic laths

effective grain size for cleavage fracture refined to around 100of nm whereas effective grain size for plastic deformation stillat micron level

Can improve toughness without impact strength 88

NANOINDENTATION It is hard to prepare indenter but the impacted volumes from test


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It is hard to prepare indenter but the impacted volumes from testproportional to indenter size

Principles of Nanoindentation

Test consist of constant load P indenter of size AHardness H =P/A

The Harder material the smaller A

difficult to measure the indentation

size Instead record load vs depth

to determine indentation size Can proposed mechanical properties from curve as elastic modulus,

stress/strain behavior, yield strength, and work hardening rate

TEM direct observe of indentation

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MECHANICALINSTABILITYOFNANOSTRUCTURES


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Instability or buckling affect reliability of nanodevices

WRINKLINGOFTHINFILMS

thin metal film deposited atop

elastic substrate cooling introduced

mismatch of shrinking between two

materials

Wrinkles under capillary force

exerted by a drop of water placed on

Surface

stress induced by surface tension about 100 times stressdeveloped due to weight drop

Spontaneous buckling of thin films on substrates canachieve order patterns due to mismatched deformation,

which can be manipulated in different ways

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B S C /S S


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BUCKLINGOFSPHEROIDALCORE/SHELLSTRUCTURES

buckling behavior on closed surface differ from on surface

with free boundaries triangular patterns self-assemble on surface of SiO2 shell

on spherical Ag core structure by cooling

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BUCKLINGOFNANOBEAMS


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Periodic nanostructures atop an elastic material, PDMS

show surface features

Euler LowAssume :ideal column straight,

homogeneous, and free from initial stress.

Assume linear strain deformations

Boundary condition free upper end

critical load

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TIMOSHENKO ENERGY METHOD


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TIMOSHENKOENERGYMETHOD

buckling of bar under distributed axial loads critical value of the uniform load for the beam

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Fundmental and Application of Nano Material