IN SOLID STATE MATERIALS CHEMISTRY - SHAPE,
SIZE AND DEFECTS ARE EVERYTHING!
• Form, habit, morphology and physical size of product controls synthesis method of choice, rate and extent of reaction and reactivity (exposed contacted crystal faces)
• Single crystal, phase pure, defect free solids do not exist and if they did not likely of much interest – any thoughts ?!?
• Single crystal (SC) that has been defect modified with dopants - intrinsic vs extrinsic or non-stoichiometry controls chemical and physical properties, function, utility
• SC preferred over microcrystalline powders for structure and properties characterization and nanocrystals have distinct size dependent properties

Used for characterization when single crystal can not be easily obtained, preferred for industrial production and certain applications, where large surface area useful like control of reactivity, catalytic chemistry, separation materials, battery and fuel cell energy materials, diffusion length control
Engineering superconducting ceramic wires, ceramic engines, aeronautical parts, magnets
Widespread use in microelectronics, optical telecommunications, photonic devices, magnetic data storage applications, coatings – protective, antireflection, self-cleaning
important for fabrication of electronic, magnetic, optical planarized devices – minimizing deleterious defects

No long range translational order – just short range local order
- control mechanical, optical-electrical-magnetic properties like fiber optic cables, fiber lasers, optical components
Quantum size effect materials – electronic, optical, magnetic devices - discrete electronic energy levels rather than continuous electronic bands – also useful in nanomedicine like diagnostics, therapeutic drug delivery, cancer therapy, imaging contrast agents MRI, CT,
PET, and fuel, battery, solar cell materials

MORE ASPECTS OF SOLID-SOLID REACTIONS
•
Conventional solid state synthesis - heating mixtures of two or more solids to form a solid phase product.
•
Repeat - unlike gas phase and solution reactions
• Limiting factor in solid-solid reactions usually diffusion, driven thermodynamically by a concentration gradient.
• Described by Fick’s law : J = -D(dc/dx)
•
J = Flux of diffusing species (#/cm 2 s)
•
D = Diffusion coefficient ( cm 2 /s )
•
(dc/dx) = Concentration Gradient (#/cm 4 )

MORE ASPECTS OF SOLID-SOLID REACTIONS
• The average distance a diffusing species will travel <x>
•
<x>

(2Dt) 1/2 where t is the time.
• To obtain good rates of reaction you typically need the diffusion coefficient D to be larger than ~ 10 -12 cm 2 /s.
• D = D o exp(-Ea/RT) diffusion coefficient increases with temperature, rapidly as you approach the melting point.
• This concept leads to empirical Tamman’s Rule :
•
Extensive reaction will not occur until T reaches at least
1/3 of the melting point of one or more of the reactants.

RATES OF REACTIONS IN SOLID STATE SYNTHESIS
ARE CONTROLLED BY THREE MAIN FACTORS
1 .
: surface area of reacting solids
2.
of ions through various phases, reactants and products
3.
of product phase

• Seems trivial - vital consideration in solid state synthesis
•
Consider MgO, 1 cm 3 cubes, density 3.5 gcm -3
•
1 cm cubes: SA 6x10 -4 m 2 /g
• 10 -3 cm cubes: SA 6x10 -1 m 2 /g (10 9 x6x10 -6 /10 4 )
•
10 -6 cm cubes: SA 6x10 2 m 2 /g (10 18 x6x10 -12 /10 4 )
• The latter is equal to a 100 meter running track!!!
•
Clearly reaction rate influenced by SA of precursors as contact area depends roughly on SA of the particles

EXTRA CONSIDERATIONS IN SOLID STATE SYNTHESIS
– GETTING PRECURSORS TOGETHER
•
High pressure squeezing of reactive powders into pellets, for instance using 10 5 psi to reduce inter-grain porosity and enhance contact area between precursor grains
• Pressed pellets can still be still 20-40% porous
pressing improves densification
NOT

Small d
Large SA/V
Small x
Large d
Small SA/V
Large x

EXTRA CONSIDERATIONS IN SOLID STATE
SYNTHESIS
• x(thickness planar layer)

1/A(contact area)
•
A(contact area)

1/d(particle size)
• Thus particle sizes and surface area connected

• Therefore A and d affect interfacial thickness x!!!

MINIMIZING DIFFUSION LENGTHS < x >

( 2Dt ) 1/2 FOR
RAPID AND COMPLETE DIRECT REACTION
BETWEEN SOLID STATE MATERIALS AT LOWEST T
Particle surface area A
Product interface thickness x
Particle size d dx/dt = k/x = k’A =k"/d
All aimed to increase A and decrease x and minimize diffusion length scale
*Decreasing particle size to nanocrystalline range
*Hot pressing densification of particles
*Atomic scale mixing in composite precursor compounds
*Coated particle - mixed component reagents, corona/core precursors
*Johnson superlattice layered precursors

MINIMIZING DIFFUSION LENGTHS <x>

(2Dt) 1/2 FOR
RAPID AND COMPLETE DIRECT REACTION
BETWEEN SOLID STATE MATERIALS AT LOWEST T
Core-corona reactants in intimate contact, made by precursor precipitation, sol-gel deposition, CVD
All aimed to increase A and decrease x and minimize diffusion length scale
COATED PARTICLE
MIXED SOLID STATE
REAGENTS

SYNTHESIS OF COMPOSITION TUNABLE
MONODISPERSE Zn x
Cd
1-x
Se ALLOY NANOCRYSTALS
ELECTRONIC BAND GAP ENGINEERING x controlled by size of core and corona more on this later

MINIMIZING DIFFUSION LENGTHS <x>

(2Dt) 1/2 FOR
RAPID AND COMPLETE DIRECT REACTION
BETWEEN SOLID STATE MATERIALS AT LOWEST T
SUPERLATTICE
REAGENTS
•Johnson superlattice precursor
•Deposition of thin film reactants
•Controlled thickness, composition
•
Metals, semiconductors, oxides
• Binary, ternary compounds
•
Modulated structures
• Solid solutions (statistical reagent mix)
•Diffusion length x control
•Thickness control of reaction rate
•Low T solid state reaction
•Designer element precursor layers
•Coherent directed product nucleation
•Oriented product crystal growth
• LT metastable hetero-structures
•
HT thermodynamic product

ELEMENT M + 2X
MODULATED
SUPERLATTICES -
DEPOSITED AND
THERMALLY POST
TREATED TO GIVE
LAYERED METAL
DICHALCOGENIDES MX
2
COMPUTER
MODELLING OF
DIFFUSION
CONTROLLED SOLID
STATE REACTION OF
JOHNSON
SUPERLATTICE

2
• M = Ti, V, Cr, Zr, Hf, Nb, Ta, Mo, W
• X = S, Se, Te
• O h
MX octahedral and D
3h
6 building blocks trigonal pyramidal
• Edge sharing trigonal packed MX
6/3 units
• Parallel stacked MX
2 layers
• Strong M-X covalent forces in layers
• Weak VdW forces between layers
• VdW gap between adjacent layers
• Chemistry between the sheets

MINIMIZING DIFFUSION LENGTHS <x>

(2Dt) 1/2 FOR
RAPID AND COMPLETE DIRECT REACTION
BETWEEN SOLID STATE MATERIALS AT LOWEST T
AT LOW T THE
SUPERLATTICE REAGENTS
YIELD SUPERLATTICE
ARTIFICIAL CRYSTAL
PRODUCT
Johnson superlattice reagent design
{(Ti-2Se)
6
(Nb-2Se)
6
} n
Low T annealing reaction
{(TiSe
2
)
6
(NbSe
2
)
6
} n
Metastable ternary modulated layered metal dichalcogenide (hcp Se 2layers,
Ti 4+ /Nb 4+ O h
/D
3h interlayer sites) superlattice well defined PXRD
Confirms correlation between precursor heterostructure sequence and superlattice ordering of final product
Note NbSe
2 is a superconductor !!!

Superlattice precursor sequence 6(Ti-2Se)-6(Nb-2Se) yields ternary modulated superlattice composition
{(TiSe
2
)
6
(NbSe
2
)
6
} n with 62 well defined PXRD reflections – good exercise – give it a try
Confirms correlation between precursor heterostructure sequence and superlattice ordering of final product

MINIMIZING DIFFUSION LENGTHS <x>

(2Dt) 1/2 FOR
RAPID AND COMPLETE DIRECT REACTION
BETWEEN SOLID STATE MATERIALS AT LOWEST T
AT HIGH T THE
SUPERLATTICE REAGENTS
YIELD HOMOGENEOUS
SOLID SOLUTION PRODUCT
Johnson superlattice reagent design
{(Ti-2Se)
6
(Nb-2Se)
6
} n
High T annealing reaction
{(Ti
0.5
Nb
0.5
Se
2
)} n
Thermodynamic linear Vegard type solid solution ternary metal dichalcogenide “alloy” product with identical layers
Properties of ternary product is the atomic fraction weighted average of binary end member components – Vegard Law
P( Ti x
Nb
(1-x)
Se
2
) = xP( Ti Se
2
) + (1-x)P Nb Se
2

ELEMENTAL MODULATED
SUPERLATTICES
•
Several important synthetic parameters and in situ probes
• Reactants prepared using standard thin film deposition techniques
– more on this later - and consist of nm scale thickness controlled layers of the elements to be reacted.
•
Elements easily substituted for another
• Allows rapid surveys over a class of related reactions and synthesis of iso-structural compounds.

ELEMENTALLY MODULATED
SUPERLATTICES
• Diffusion distance is determined by the multilayer repeat distance which can be continuously varied
• An important advantage, allowing experimental probe of reaction kinetics and mechanism as a function of inter-diffusion distance and temperature
• Multi-layer repeat distances easily verified in prepared reactants and products made under different conditions using low angle XRD
•
Think about how to make a BaTiO3-SrTiO3 Perovskite superlattice or a
MgAl2O4-ZnAl2O4 Spinel superlattice and then a BaxSr1-xTiO3 and
MgxZn1-xAl2O4 solid solution ??? and why would you do this ???

CORE-CORONA NANOCLUSTER PRECURSOR BASED
KIRKENDALL SYNTHESIS OF HOLLOW NANOCLUSTERS
S
Co e(-)
Co(3+)
V[Co]
S(2-)
Co
2
S
3
•
Synthesis of surfactant-capped cobalt nanoclusters :
• Co(III) precursor (acetate, acetylacetonate) - NaBH
4
• with surfactants - oleic acid or oleylamine  Co n
L m reductant
• arrested nucleation and growth of ligand capped cobalt nanoclusters
• surfactant functions as high temperature capping ligand and solvent
• then surfactant-sulfur injection - coating of sulfur shell on nanocluster
• cobalt sesquisulfide Co
2
S
3 product shell layer formed at interface

17
33
2
Arrested nucleation and growth of nanocrystals – use of surfactant, ligand, high temperature solvent properties

CORE-CORONA NANOCLUSTER PRECURSOR BASED KIRKENDALL
SYNTHESIS OF HOLLOW NANOCLUSTERS
S
Co e(-)
Co(3+)
V[Co]
S(2-)
Co
2
S
3
• counter-diffusion of Co(3+)/2e(-) and S(2-) across thickening shell
• faster diffusion of Co(3+) than S(2-) creates vacancies V[Co] in core
• size rather than charge effect determines diffusion
• generated vacancies agglomerate in core to form a void
• hollow core created which grows as the product shell thickens
• end result – a hollow nanosphere made of nc cobalt sesquisulfide Co
2
• shell not perfectly sealed - has some porosity between nanocrystals –
S
3
• magnetic drug delivery and magnetohyperthermia cancer therapeutics

I don’t believe it !!!
THINGS ARE NEVER
THAT SIMPLE!!!
Different diffusion processes in the growth of different architecture hollow nanostructures induced by the Kirkendall effect
Air vacancies white, cobalt orange, Co2S3 product blue
Small Sept 2007

Time evolution of a hollow Co
2
S
3 nanocrystal grown from a
Co nanocrystal via the nanoscale Kirkendall effect
Science 2004, 304, 711

TURNING NANOSTRUCTURES INSIDE-OUT
• Kirkendall effect - discovered in 1930’s.
• Occurs during reaction of two solid-state materials and involves the counter diffusion of reactant species, like ions, across product interface usually at different rates.
• Special case of movement of fast-diffusing component cannot be balanced by movement of slow component the net mass flow is accompanied by a net flow of atomic vacancies in the opposite direction.
•
Leads to
formed through super-saturation of vacancies into hollow pores

TURNING NANOSTRUCTURES INSIDE-OUT
• When starting with perfect building blocks such as monodisperse cobalt nanocrystals a reaction meeting the Kirkendall criteria can lead to supersaturation and agglomeration of vacancies exclusively in the center of the nanocrystal .
•
General route to hollow nanocrystals of almost any given material and shape – like nanocubes, nanotriangles, nanorods and chains of nanoshells
• First proof-of-concept experiment - synthesis of
Co
2
S
3 nanoshell starting from Co nanocluster.

Time evolution of a hollow CoSe
2 nanocrystal magnetic dipole chain grown from a Co nanocrystal and selenium in surfactant capping ligand and solvent via the nanoscale Kirkendall effect – Small September 2007

Scheme of magnetic dipole-dipole coupling of superparamagnetic nanocrystals into magnetic nanocrystal chains
Superparamagnetism – cooperative magnetic coupling of unpaired electron spins in a single Weiss domain ferromagnetic nanocrystal

Magnetotactic bacteria – vesicle templated nucleation and growth of superparamagnetic nanocrystal dipole chain
Communication and cooperative behaviour between bacteria communities – relevant to evolutionary biology ???

Works for Hollow ZnAl
2
O
4
Spinel Nanotubes!!!

Hollow ZnAl
2
O
4
Spinel Nanotubes
• How does it work – VPT VLS growth (see later)
• ZnO(s) +C(s)  ZnCO(g)
• Au n
(l) + ZnCO(g)  ZnO(NW) + C(s)
• Coat ZnO NW with hydrolysable-polymerizable AlX3 (X = Cl,
OR) precursor in solution or vapor phase – solgel chemistry
• AlX3 + 3H2O  Al(OH)3 + 3HCl
• AlOH + HOAl  Al-O-Al + H2O
• Thermally treat to make Al2O3 coated ZnO NWs
• Heat further to induce interdiffusion of core and corona
• Zn2+ more mobile than Al3+
• Creates Zn2+ vacancies in the core ZnO nanowire
• Vacancies agglomerate in core and create Kirkendall porosity
• Final product a ZnAl2O4 hollow Spinel nanotube
• And what would you use them for – nanofluidics, ionic nanodiode or transistor, drug storage and delivery vehicle
???

NANOSCALE PATTERNING OF SHAKE-AND-BAKE
SOLID-STATE CHEMISTRY
MINIMIZING DIFFUSION LENGTHS
<x>

(2Dt) 1/2 FOR RAPID AND COMPLETE
DIRECT REACTION BETWEEN SOLID STATE
MATERIALS AT LOWEST T
Younan Xia

(H
3
C)
3
SiO[Si(CH
3
)
2
O] n
Si(CH
3
)
3 n Si(CH3)2Cl2 + n H2O → [Si(CH3)2O]n + 2n HCl
Condensation polymerization synthesis of PDMS - a very famous polymer – elastomeric and hydrophobic
let’s make a micromold and do chemistry

PDMS MASTER FOR SOFT LITHOGRAPHY
MICROCONTACT PRINTING m
CP
Whitesides

Whitesides
PDMS MASTER
•
Schematic illustration of the procedure for casting PDMS replicas from a master having relief structures on its surface.
• The master is silanized and made hydrophobic by exposure to
CF
3
(CF
2
)
6
(CH
2
)
2
SiCl
3 vapor
• SiCl bind to surface OH groups and anchor perfluoroalkylsilane to surface of silicon master CF
3
(CF
2
)
6
(CH
2
)
2
SiO
3 for easy removal of PDMS mold prevents adhesive tearing of mold
•
Each master can be used to fabricate more than 50 PDMS replicas.
•
Representative ranges of values for h, d, and l are 0.2 - 20, 0.5 - 200, and 0.5 -
200 mm respectively.

NANOSCALE PATTERNING OF SHAKE-AND-BAKE
SOLID-STATE CHEMISTRY
Younan Xia

NANOSCALE PATTERNING OF SHAKE-AND-BAKE
SOLID-STATE CHEMISTRY
Co(NO
3
)
2
Co
3
O
4
Co
(A) Optical micrograph (dark field) of an ordered 2-D array of nanoparticles of Co(NO
3
)
2 that was fabricated on a Si/SiO
2 substrate by selective dewetting from a 0.01 M nitrate solution in 2-propanol.
The surface was patterned with an array of hydrophilic Si-SiO
2 separated by 5 m m.
grids of 5 x 5 m m 2 in area and
(B) An SEM image of the patterned array shown in
(A), after the nitrate had been decomposed into Co
3
O
4 by heating the sample in air at 600 °C for 3 h. These
Co
3
O
4 particles have a hemispherical shape (see the inset for an oblique view) – ferromagnetic or superparamagnetic depending on size
(C) An AFM image (tapping mode) of the 2-D array shown in (B), after it had been heated in a flow of hydrogen gas at 400 °C for 2 h. These Co particles were on average 460 nm in lateral dimensions and 230 nm in height – ferromagnetic or superparamagnetic .

NANOSCALE PATTERNING OF SHAKE-AND-BAKE
SOLID-STATE CHEMISTRY
MgFe
2
O
4
NiFe
2
O
4
AFM image of an ordered 2-D array of (A)
MgFe
2
O
4 and (B) NiFe
2
O
4 that was fabricated on the surface of a Si/SiO
2 substrate by selective dewetting from the 2-propanol solution (0.02 M) that contained a mixture of two nitrates [e.g. 1:2 between Mg(NO
3
)
2 and Fe(NO
3
)
3
].
The PDMS stamp contained an array of parallel lines that were 2 mm in width and separated by 2 mm. Twice stamped orthogonally.
Citric acid HOC(CH2CO2H)3 forms atomically mixed Mg(II)/Fe(III) multidentate complex added to reduce the reaction temperature between these two nitrate solids in forming the ferrite.
Ferrite nanoparticles ~300 nm in lateral dimensions and ~100 nm in height.

GOING EVEN SMALLER WITH DIP PEN NANOLITHOGRAPHY
Throw Away the Micron Scale PDMS Stamp – Use a nm Scale AFM Tip
• Direct-write "dip-pen" nanolithography (DPN) has been developed
•
Delivers collections of molecules in a positive printing mode
• Proof-of concept
• Alkanethiols on gold controls surface wettability, chemical reactivity at scale well below a micron
Chad Mirkin, Science 283, 661, 1999

PATTERNING INORGANIC SOLID-STATE CHEMISTRY VIA DIP-
PEN NANOLITHOGRAPHY WITH SOL-GEL -BASED INKS
Pluronic PPO-PEO-PPO triblock copolymer surfactant solvent and carrier to enable solgel chemistry

tin oxide
Nano gas sensor silicon oxide
Nano optical waveguide aluminum oxide
Nano catalyst support calcined

SO YOU THOUGHT YOU SAW EVERYTHING!!!
Massively parallel DPN with a passive 2D cantilever array - 55,000 Tips – really pushing the envelope for solid state nanomaterials synthesis !!!
Angew Chem Int Ed., Mirkin et al, 25 th September 2005

generate approximately
88,000,000 million dot features
Each pen generated 1600 dots in a 40 x 40 array, where the dot-to-dot distance was 400 nm.
The dots had a diameter of
(100±20) nm, a height of 30 nm, and were spaced by 20 m m in the x direction and 90 m m in the y direction corresponding to the distances determined by the array architecture.

DOING ‘REAL’ SOLID STATE SYNTHESIS IN THE LAB
DIRECT REACTION OF SOLIDS - “SHAKE-AND-BAKE” SOLID STATE SYNTHESIS
•
Although this approach may seem to be ad hoc and a little irrational at times, the technique has served solid state chemistry for well over the past 50 years
•
It has given birth to the majority of high technology devices and products that we take for granted every day of our lives
•
Thus it behooves us to look critically and carefully at the methods used in the lab if one is to move beyond trial-anderror methods to the new solid state chemistry and a rational and systematic approach to synthesis of materials

THINKING ABOUT MIXING SOLID REAGENTS
• Drying reagents MgO/Al
2
O
3 maximum SA
200-800°C,
•
In situ decomposition of precursors at 600-800°C
MgCO
3
/Al(OH)
3

MgO/Al
2
O
3

MgAl
2
O
4
•
Intimate mixing of precursor reagents
•
Homogenization of solid reactants using organic solvents, grinding, ball milling , ultra-sonification

THINKING ABOUT CONTAINER MATERIALS
•
Chemically inert crucibles, boats
•
Noble metals Nb, Ta, Au, Pt, Ni, Rh, Ir
•
Refractories, alumina, zirconia, silica, boron nitride, graphite
•

THINKING ABOUT SOLID STATE SYNTHESIS
HEATING PROGRAM
• Furnaces, RF, microwave, lasers, ion and electron beams
•
Prior reactions and frequent cooling, grinding and regrinding boost SA of reacting grains
•
Overcoming sintering, grain growth, brings up SA, fresh surfaces, enhanced contact area
• Pellet and hot press reagents – densification and porosity reduction, higher surface contact area, enhances rate, extent of reaction
• Care with unwanted preferential component volatilization if T too high, composition dependent
• Need INERT atmosphere for unstable oxidation states

PRECURSOR SOLID STATE SYNTHESIS METHOD
•
Co-precipitation
- high degree of homogenization, high reaction rate - applicable to nitrates, acetates, citrates, carboxylates, oxalates, alkoxides, b
-diketonates, glycolates
•
: precursors to magnetic Spinels – tunable magnetic recording media
•
Zn(CO
2
)
2
/Fe
2
[(CO
2
)
2
]
3
/H
2
O 1 : 1 solution phase mixing
• H
2
O evaporation, salts co-precipitated – solid solution mixing on atomic/molecular scale, filter, calcine in air
•
Zn(CO
2
)
2
+ Fe
2
[(CO
2
)
2
]
3

ZnFe
2
O
4
+ 4CO + 4CO
2
•
High degree of homogenization, smaller diffusion lengths, fast rate at lower reaction temperature

PROBLEMS WITH CO-PRECIPITATION METHOD
•
• Similar salt solubilities
•
Similar precipitation rates
•
Avoid super-saturation as poor control of co-precipitation
• Useful for synthesizing complex oxides like Spinels,
Perovskites
•

•
Precisely known stoichiometry double salts have controlled element stoichiometry:
3
6
3
2
17
3
• Basic double acetate pyridinate
•
Burn off organics at 200-300 o C, then calcine at 1000 o C in air for 2-3 days
•
Product highly crystalline phase pure
2
O
4 spinel

•
Chromite Spinel Precursor compound Ignition T, o C
• MgCr
2
O
4
• NiCr
2
O
4
• MnCr
2
O
4
•
CoCr
2
O
4
•
CuCr
2
O
4
•
ZnCr
2
O
4
• FeCr
2
O
4
(NH
4
)
2
Mg(CrO
4
)
2
.6H
2
O 1100-1200
(NH
4
)
2
Ni(CrO
4
)
2
.6H
2
O 1100
MnCr
2
O
7
.4C
5
H
5
N
CoCr
2
O
7
.4C
5
H
5
N
(NH
4
)
2
Cu(CrO
4
)
2
.2NH
3
(NH
4
)
2
Zn(CrO
4
)
2
. 2NH
3
(NH
4
)
2
Fe(CrO
4
)
2
1100
1200
700-800
1400
1150
Good way to make chromite Spinels, important tunable magnetic materials juggling electronic-magnetic properties of the A O h and B T d ions in the Spinel lattice

• Direct heating of solid state precursors is of limited value in this respect – lack of stoichiometry, size and morphology control
•
BaCO
3
(s) + TiO
2
(s)

BaTiO
3
(s)
• Sol-gel reagents useful to create
barium titanate precursor with correct stoichiometry

SINGLE SOURCE PRECURSOR SYNTHESIS OF
BARIUM TITANATE - FERROELECTRIC MATERIAL
•
Ti(OBu)
4
(aq) + 4H
2
O

Ti(OH)
4
(s) + 4BuOH(aq)
•
Ti(OH)
4
(s) + C
2
O
4
2(aq)

TiO(C
2
O
4
)(aq) + 2OH (aq) + H
2
O
•
Ba 2+ (aq) + C
2
O
4
2(aq) + TiO( C
2
O
4
)(aq)

Ba [ Ti O( C
2
O
4
)
2
](s)
• Precipitate contains barium and titanium in correct ratio and at
920

C decomposes to barium titanate according to:
• Ba [ Ti O( C
2
O
4
)
2
](s)

Ba Ti O
3
(s) + 2CO

(g) + 2CO
2

(g)
•
Grain size important for control of ferroelectric properties !!!
• Used to grow single crystals hydrothermally – see later – synthesis in high T high P aqueous environment

BASICS: FERROELECTRIC BARIUM TITANATE
Paraelectric a = 4.018Å Ferroelectric a = 3.997Å, c = 4.031Å
Displacive
Transition
Ti moves off center
Above 120

C (T c
) - Cubic perovskite equivalent O-Ti-O bonds in BaTiO
3
Below T c
Tetragonal perovskite long-short axial O-Ti—O bonds induced aligned electric dipoles in BaTiO
3
Note - small grains – complications - tetragonal to cubic surface gradients ferroelectricity is particle size dependent and can be lost
Multidomain fe rroelectric dipoles align in E field below T c
Cubic dielectric above T c state - below T c
– paraelectric multi-domain state with cooperative electric dipole interactions within each domain – aligned in domain but randomly oriented between domains
Single domain superparaelectric

HYSTERESIS OF POLARIZATION OF
FERROELECTRIC BaTiO
3
IN APPLIED FIELD E
Field E
Aligned domain ferroelectric Random domain dielectric
Ps saturation polarization
Pr remnant polarization
Ec coercive field
Pr
P
Ps
Pc
Single domain superparaelectric
E
Polarization Hysteresis Behavior P vs E
Diagnostic of Ferroelectric

Polarization Switching by Changing Direction of Applied Electric Field
DPN Direct Reaction Solid State Chemistry
Synthesis of Ferroelectric PbTiO3 Array
Synthesis Precursor Sol


• Schematic drawings illustrating the dip-pen nanolithography
(DPN) of ferroelectric PbTiO3
(PTO) nanodots.
• (a) Patterns of PTO nanodots formed by DPN.
• (b) Formation of a nanopattern using a PTO precursor sol on the surface of epitaxially mateched Nb-doped SrTiO3 by
DPN.
• (c) To obtain highly crystallized
• PTO nanodots, an annealing process is carried out after the lithography of the PTO nanopattern is performed.
Conducting AFM tip and substrate enable PFM and
EFM ferroelectricity measurements on individual dots

DPN Size and Thickness Control of PbTiO3 Nanodots

DPN PbTiO3 Nanodots – How Small Can You Go?

DPN Synthesis of FeRAM – Characterization of Ferroelectricity By
Piezoelectric and Electric Field Force Microscopy (PFM, EFM)

SOL-GEL SINGLE SOURCE PRECURSORS TO LITHIUM
NIOBATE - NLO MATERIAL
•
•
LiOEt + EtOH + Nb(OEt)
• LiNb(OEt)
Li Nb (OEt)
6 n
+ H
2
(OH)
5
O

LiNb(OEt)
6-n
+
D
+ O
2

LiNb(OEt)
6 n
(OH)

LiNbO
3
6-n
  gel

Li Nb O
3
•
Lithium niobate, ferroelectric Perovskite, nonlinear optical NLO material, used as electrooptical switch – voltage control of refractive index – random vs aligned electric dipoles
• Bimetallic alkoxides - single source precursor
•
Sol-gel chemistry - hydrolytic polycondensation
 gel
• MOH + M’OH  MOM’ + H
2
O
• Yields glassy product
• Sintering product in air - induces crystallization

INDIUM TIN OXIDE –ITO – CHANGED THE WORLD!
•
Indium sesquioxide In
2
O
3
(wide Eg semiconductor) electrical conductivity enhanced by n-doping with (10%) Sn(4+)
• ITO is Sn n
In
2-n
O
3
• ITO is optically transparent - electrically conducting - thin films are vital as electrode material for solar cells, electrochromic windows/mirrors,
LEDs, OLEDs, LC displays, electronic ink, photonic crystal ink and so forth
• Precursors - EtOH solution of (2-n)In(OBu)
3
/nSn(OBu)
4
• Hydrolytic poly-condensation to form gel, spin coat gel onto glass substrate to make thin film: InOH + HOSn  InOSn
• Dry gel at 50-100

C, heat at 350

C in air to produce ITO
• Check electrical conductivity and optical transparency

• ITO
: Sn doped In2O3 - 1: 9 solid solution – electrons in CB
• n-doped with Sn(IV) isomorphously replacing In(III)
• ATO
: Sb doped SnO2 – how would you make it?
• n-doped with Sb(V) isomorphously replacing Sn(IV)
• FTO
: F doped SnO2 – how would you make it?
• n-doped with F(-I) isomorphously replacing O(-II)
• AZO
: Al doped ZnO – how would you make it ?
• n-doped with Al(III) isomorphously replacing Zn(II)

NOT
• Objective is to optimize optical transparency and electrical conductivity
• ITO – Sn:In = 1: 9 solid solution – Linear Vegard Law
• Si classical semiconductor doping normally ppm B and P dopants
• Contrast higher ITO doping creates some [O] vacancies
• To balance Sn(IV) vs In(III) charge differences
• Reality – general formula of ITO
• In
2-x
Sn x
O
3-2x
• Replacing xIn(III) with xSn(IIV) requires 2x[O(-II)]
• Effect is to reduces number of electron n-dopants
• Reduces conductivity
• Also some unwanted Sn(II) formed in synthesis introduces holes
 s
= s e
+ s h
• Reduces conductivity
• Optimizing electrical conductivity of ITO by materials chemistry is not so simple

A Nanomaterial that Could
Change the World
How, Why, When !!! ???

• Optical transparency and electrical conductivity of TCO’s critical for thin layer electrodes in a wide range of high technology devices
• Solar cells
• Flat panel displays
• Smart energy saving electrochromic windows
• Electronics
• Chemical sensors
• OLEDs
• Lasers
• Currently industry favourite is ITO on glass
• Made by vacuum thermal deposition or sputter deposition
• Works on thermally stable substrates but not on plastics
• ITO expensive as In rare – Canada is a major supplier !!!
• Dire need for low cost easy to make alternative
• Film formation at RT on plastic substrates would be great asset
• Example of how to get rich quickly through materials chemistry

Benzyl Alcohol High T
Solvent and Reactant
Source of Oxygen in
Non-Aqueous SolGel
Chemistry

• Benzyl Alcohol solvent and source of oxygen

• Or



• Wide bandgap optically transparent semiconductor Eg = 3.6eV and n-doped
• Control over size, shape, surface charge allows colloidally and air stable dispersions in common solvents like H2O, EtOH, THF
• Note add a little acid to water dispersion - colloidally stable
• Enable thin films and patterns to be made on any substrate under ambient conditions
• Spin, dip, aerosol, IJP coating and printing strategies
• Synthesis non-aqueous solgel
• Arrested nucleation and growth of ncATO
• Solvent and reactant benzyl alcohol C6H5CH2OH
• Reagent precursors SbCl3, Sb(OEt)3, Sb(O2CCH3)3
• Anhydrous synthesis conditions 150oC, 2 hours

•
Morphology, size and dispersibility of
ATO nanoparticles:
• STEM-HAADF images of 10 % ATO nanoparticles prepared using Sb(ac)3 at 100 oC (a) and Sb(ac)3 at 150 oC
(b).
• The insets 6 x 6 nm in size show high resolution STEM-HAADF images of a single nanoparticle.
• Size distribution of 10 % ATO nanoparticles prepared using Sb(ac)3 at 150 oC determined from HRTEM images of ca. 100 nanoparticles (gray bars) and from DLS measurement (red line) of a colloidal dispersion in EtOH of the same nanoparticles
• (c). The inset 6 x 6 nm in size shows high resolution TEM image of a single nanoparticle.
• Images of as prepared differently doped ATO nanoparticles synthesized at 150 °C using Sb(ac)3 (d): dried particles (top) and their colloidal dispersions in THF (particle concentration of 5 wt%) (bottom).

• Key objectives in nanochemistry strategy
• Command over size, shape, surface charge
• Composition and solvent solubility/dispersibility
• PXRD – phase purity and particle size
• HRTEM, DLS – particle size and particle size distribution
• XPS – Sb(V) : Sb(III)
• EDX – elemental compositition

Top Down NanoFabrication - High Spatial Resolution Patterning at the Nanoscale Using Energetic Short Wavelength Electron Beams

SUB -10 NM NANOSCALE
DIRECT SOLID STATE REACTION – TiO2
Electron Beam Nanolithography of Spin-Coated Sol-Gel TiO
2
Based Resists
LOCALIZED HEATING AT THE NANOMETER SCALE benzoyl acetone tetrabutoxyorthotitanate
Choosing the right solid state precursor to make resist

SUB -10 NM NANOSCALE
DIRECT SOLID STATE REACTION
Electron Beam Nanolithography Using Spin-Coated TiO
2
Resists
Choosing the right solid state precursor
•
Utilization of spin-coated sol gel based TiO
2 resists by chemically reacting titanium n-butoxide with benzoylacetone in methyl alcohol.
•
They have an electron beam sensitivity of 35 mC cm 2 and are >10 7 times more sensitive to an electron beam than sputtered
TiO
2 and crystalline TiO
2 films.

Sub-10 nm Electron Beam Nanolithography
Using Spin-Coated TiO
2
Resists
• Fourier transform infrared studies suggest that exposure to an electron beam results in the gradual removal of organic material from the resist .
• This makes the exposed resist insoluble in organic solvents such as acetone, unexposed is soluble, thereby providing high-resolution negative patterns as small as 8 nm wide.
Choosing the right solid state precursor
•
Such negative patterns can be written with a pitch as close as 30 nm.

Nanometer scale precision structures
Nanoscale TiO
2 structures offer new opportunities for developing next generation solar cells, optical wave-guides, gas sensors, electrochromic displays, photocatalysts, photocatalytic mCP, battery materials

Nanometer scale tolerances