Download - 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.
Comp. of lower layers43
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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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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TIMOSHENKOENERGYMETHOD
buckling of bar under distributed axial loads critical value of the uniform load for the beam
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