in solid state materials chemistry - shape, size and defects are everything! form, habit, morphology...

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

SHAPE IS EVERYTHING!• Microcrystalline powder 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

• Polycrystalline shapes like pellet, tube, rod, wire made of microcrystal forms Engineering super-conducting ceramic wires, ceramic engines, aeronautical parts, magnets

• Single crystal or polycrystalline film Widespread use in microelectronics, optical telecommunications, photonic devices, magnetic data storage applications, coatings – protective, antireflection, self-cleaning

• Epitaxial film – single and multilayer superlattice films - lattice matching with substrate - tolerance factor - elastic strain, defects important for fabrication of electronic, magnetic, optical planarized devices – minimizing deleterious defects

SHAPE IS EVERYTHING!

• Non-crystalline – amorphous - glassy - fibers, films, tubes, plates No long range translational order – just short range local order - control mechanical, optical-electrical-magnetic properties like fiber optic cables, fiber lasers, optical components

• Nanocrystalline – below a certain dimensions properties of materials scale with size 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 (#/cm2s)

• D = Diffusion coefficient (cm2/s)

• (dc/dx) = Concentration Gradient (#/cm4)

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 cm2/s.

• D = Doexp(-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 1/31/3 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. Contact area: surface area of reacting solids

2. Rates of diffusion: of ions through various phases, reactants and products

3. Rate of nucleation: of product phase

Let us examine each of the above in turnLet us examine each of the above in turn

SURFACE AREA OF PRECURSORSSURFACE AREA OF PRECURSORS

• Seems trivial - vital consideration in solid state synthesis

• Consider MgO, 1 cm3 cubes, density 3.5 gcm-3

• 1 cm cubes: SA 6x10-4 m2/g • 10-3 cm cubes: SA 6x10-1 m2/g (109x6x10-6/104)• 10-6 cm cubes: SA 6x102 m2/g (1018x6x10-12/104)

• 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 105 psi to reduce inter-grain porosity and enhance contact area between precursor grains

• Pressed pellets can still be still 20-40% porous

• Hot pressing improves densification

• Note: contact area NOT in planar layer lattice diffusion model for thickness change with time, dx/dt = k/x

• How do we think about this???How do we think about this???

Thinking About A, d, x Particle Relations

Small d Large d

Large SA/V Small SA/V

Small x 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 connectedThus particle sizes and surface area connected

• Hence x d

• Therefore A and d affect interfacial thickness x!!!

• These relations suggest some strategies for rate enhancement in direct solid state reactions by controlling diffusion lengths!!! controlling diffusion lengths!!!

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

*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

All aimed to increase A and decrease x and minimize diffusion length scale



All aimed to increase A and decrease x and minimize diffusion length scale

Core-corona reactants in intimate contact, made by precursor precipitation, sol-gel deposition, CVD

COATED PARTICLE MIXED SOLID STATE REAGENTS

SYNTHESIS OF COMPOSITION TUNABLE MONODISPERSE ZnxCd1-xSe ALLOY NANOCRYSTALS

ELECTRONIC BAND GAP ENGINEERINGELECTRONIC BAND GAP ENGINEERING

x controlled by size of core and corona more on this later



•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

SUPERLATTICE SUPERLATTICE REAGENTSREAGENTS

ELEMENT M + 2X MODULATED

SUPERLATTICES -DEPOSITED AND

THERMALLY POST TREATED TO GIVE LAYERED METAL

DICHALCOGENIDES MX2

COMPUTER MODELLING OF

DIFFUSION CONTROLLED SOLID STATE REACTION OF

JOHNSON SUPERLATTICE

Metal Dichalcogenides MXMetal Dichalcogenides MX22

• M = Ti, V, Cr, Zr, Hf, Nb, Ta, Mo, W• X = S, Se, Te

• Oh octahedral and D3h trigonal pyramidal MX6 building blocks

• Edge sharing trigonal packed MX6/3 units

• Parallel stacked MX2 layers

• Strong M-X covalent forces in layers• Weak VdW forces between layers• VdW gap between adjacent layers• Chemistry between the sheets



Johnson superlattice reagent design

{(Ti-2Se)6(Nb-2Se)6}n

Low T annealing reaction

{(TiSe2)6(NbSe2)6}n

Metastable ternary modulated layered metal dichalcogenide (hcp Se2- layers, Ti4+/Nb4+ Oh/D3h interlayer sites) superlattice well defined PXRD

Confirms correlation between precursor heterostructure sequence and superlattice ordering of final product

Note NbSeNote NbSe22 is a superconductor !!! is a superconductor !!!

AT LOW T THE SUPERLATTICE REAGENTS YIELD SUPERLATTICE ARTIFICIAL CRYSTAL PRODUCT

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



Johnson superlattice reagent design

{(Ti-2Se)6(Nb-2Se)6}n

High T annealing reaction

{(Ti0.5Nb0.5Se2)}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(TixNb(1-x)Se2) = xP(TiSe2) + (1-x)PNbSe2

AT HIGH T THE SUPERLATTICE REAGENTS YIELD HOMOGENEOUS SOLID SOLUTION PRODUCT

• 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.

ELEMENTAL MODULATED ELEMENTAL MODULATED SUPERLATTICESSUPERLATTICES

ELEMENTALLY MODULATED ELEMENTALLY MODULATED SUPERLATTICESSUPERLATTICES

• 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

V[Co]

Co(3+)

S(2-)

e(-)

Co

S

Co2S3

• Synthesis of surfactant-capped cobalt nanoclusters:

• Co(III) precursor (acetate, acetylacetonate) - NaBH4 reductant • with surfactants - oleic acid or oleylamine ConLm • 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 Co2S3 product shell layer formed at interface

Oleic Acid C17H33CO2H

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

CORE-CORONA NANOCLUSTER PRECURSOR BASED KIRKENDALL SYNTHESIS OF HOLLOW NANOCLUSTERS

V[Co]

Co(3+)

S(2-)

e(-)

Co

S

Co2S3

• 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 Co2S3

• shell not perfectly sealed - has some porosity between nanocrystals – • magnetic drug delivery and magnetohyperthermia cancer therapeutics

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 I don’t believe it !!!

Time evolution of a hollow Co2S3 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 Kirkendall porosity 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 super-saturation 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 Co2S3 nanoshell starting from Co nanocluster.

Time evolution of a hollow CoSehollow CoSe22 nanocrystal magnetic nanocrystal magnetic

dipole chaindipole 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

I know my magnetic North !!!

Communication and cooperative behaviour between bacteria communities – relevant to evolutionary biology ???

Works for Hollow ZnAl2O4 Spinel Nanotubes!!!

Hollow ZnAl2O4 Spinel Nanotubes

• How does it work – VPT VLS growth (see later)• ZnO(s) +C(s) ZnCO(g) • Aun(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 And what would you use them for – nanofluidics, ionic

nanodiode or transistor, drug storage and delivery vehicle nanodiode or transistor, drug storage and delivery vehicle ??? ???

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

Younan Xia

MINIMIZING DIFFUSION LENGTHS <x> (2Dt)1/2 FOR RAPID AND COMPLETE

DIRECT REACTION BETWEEN SOLID STATE MATERIALS AT LOWEST T

Tutorial - Surface Chemistry of Silica

Polydimethylsiloxane PDMS

(H3C)3SiO[Si(CH3)2O]nSi(CH3)3

Condensation polymerization synthesis of PDMS - a very famous polymer – elastomeric and hydrophobic

- let’s make a micromold and do chemistry

n Si(CH3)2Cl2 + n H2O → [Si(CH3)2O]n + 2n HCl

PDMS MASTER FOR SOFT LITHOGRAPHY

MICROCONTACT PRINTING CP

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 CF3(CF2)6(CH2)2SiCl3 vapor

• SiCl bind to surface OH groups and anchor perfluoroalkylsilane to surface of silicon master CF3(CF2)6(CH2)2SiO3 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.

Whitesides


Younan Xia


(A) Optical micrograph (dark field) of an ordered 2-D array of nanoparticles of Co(NO3)2 that was fabricated on a Si/SiO2 substrate by selective de-wetting from a 0.01 M nitrate solution in 2-propanol. The surface was patterned with an array of hydrophilic Si-SiO2 grids of 5 x 5 m2 in area and separated by 5 m.

(B) An SEM image of the patterned array shown in (A), after the nitrate had been decomposed into Co3O4 by heating the sample in air at 600 °C for 3 h. These Co3O4 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 .

Co(NO3)2

Co3O4

Co


AFM image of an ordered 2-D array of (A) MgFe2O4 and (B) NiFe2O4 that was fabricated on the surface of a Si/SiO2 substrate by selective de-wetting from the 2-propanol solution (0.02 M) that contained a mixture of two nitrates [e.g. 1:2 between Mg(NO3)2 and Fe(NO3)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.

MgFe2O4

NiFe2O4

BEYOND MICROCONTACT PRINTING GOING EVEN SMALLER WITH DIP PEN NANOLITHOGRAPHYGOING EVEN SMALLER WITH DIP PEN NANOLITHOGRAPHY

Throw Away the Micron Scale PDMS Stamp – Use a nm Scale AFM TipThrow 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 aluminum oxide

silicon oxide calcined

Nano gas sensor

Nano catalyst support

Nano optical waveguide

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, 25th September 2005

SO YOU THOUGHT YOU SAW EVERYTHING!!!

HOW GOOD???55,000-pen array was used togenerate approximately 88,000,000 million dot features

Each pen generated 1600 dots in a 40 x 40 array, where thedot-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 in the x direction and 90 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 SYNTHESISDIRECT 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-and-error methods to the new solid state chemistry and a rational and systematic approach to synthesis of materials

THINKING ABOUT MIXINGMIXING SOLID REAGENTS

• Drying reagents MgO/Al2O3 200-800°C, maximum SA

• In situ decomposition of precursors at 600-800°C MgCO3/Al(OH)3 MgO/Al2O3 MgAl2O4

• Intimate mixing of precursor reagents

• Homogenization of solid reactants using organic solvents, grinding, ball milling, ultra-sonification

THINKING ABOUT CONTAINERCONTAINER MATERIALS

• Chemically inert crucibles, boats

• Noble metals Nb, Ta, Au, Pt, Ni, Rh, Ir

• Refractories, alumina, zirconia, silica, boron nitride, graphite

• Reactivity with containers at high Reactivity with containers at high temperatures needs to be carefully temperatures needs to be carefully evaluated for each system – know your evaluated for each system – know your solid state chemistrysolid state chemistry

THINKING ABOUT SOLID STATE SYNTHESIS HEATINGHEATING 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

PRECURSORPRECURSOR SOLID STATE SYNTHESIS METHOD

• Co-precipitation - high degree of homogenization, high reaction rate - applicable to nitrates, acetates, citrates, carboxylates, oxalates, alkoxides, -diketonates, glycolates

• Concept: precursors to magnetic Spinels – tunable magnetic recording media

• Zn(CO2)2/Fe2[(CO2)2]3/H2O 1 : 1 solution phase mixing

• H2O evaporation, salts co-precipitated – solid solution mixing on atomic/molecular scale, filter, calcine in air

• Zn(CO2)2 + Fe2[(CO2)2]3 ZnFe2O4 + 4CO + 4CO2

• High degree of homogenization, smaller diffusion High degree of homogenization, smaller diffusion lengths, fast rate at lower reaction temperaturelengths, fast rate at lower reaction temperature

PROBLEMS WITH CO-PRECIPITATION METHOD

• Co-precipitation requirements:

• Similar salt solubilities

• Similar precipitation rates

• Avoid super-saturation as poor control of co-precipitation

• Useful for synthesizing complex oxides like Spinels, Perovskites

• Disadvantage: often difficult to prepare high purity, accurate stoichiometric phases

DOUBLE SALTDOUBLE SALT PRECURSORS

• Precisely known stoichiometry double salts have controlled element stoichiometry:

• Ni3Fe6(CH3CO2)17O3(OH).12Py

• Basic double acetate pyridinate

• Burn off organics at 200-300oC, then calcine at 1000oC in air for 2-3 days

• Product highly crystalline phase pure NiFe2O4 spinel

Good way to make chromite Spinels, important tunable magnetic materialsjuggling electronic-magnetic properties of the A Ojuggling electronic-magnetic properties of the A Ohh and B T and B Tdd ions in the Spinel lattice ions in the Spinel lattice

• Chromite Spinel Precursor compound Ignition T, oC

• MgCr2O4 (NH4)2Mg(CrO4)2.6H2O 1100-1200

• NiCr2O4 (NH4)2Ni(CrO4)2.6H2O 1100

• MnCr2O4 MnCr2O7.4C5H5N 1100

• CoCr2O4 CoCr2O7.4C5H5N 1200

• CuCr2O4 (NH4)2Cu(CrO4)2.2NH3 700-800

• ZnCr2O4 (NH4)2Zn(CrO4)2. 2NH3 1400

• FeCr2O4 (NH4)2Fe(CrO4)2 1150

DOUBLE SALTDOUBLE SALT PRECURSORS

PEROVSKITE FERROELECTRICS BARIUM TITANATE

• Control of grain size determines ferroelectric properties, important for capacitors, microelectronics

• Direct heating of solid state precursors is of limited value in this respect – lack of stoichiometry, size and morphology lack of stoichiometry, size and morphology controlcontrol

• BaCO3(s) + TiO2(s) BaTiO3(s)

• Sol-gel reagents useful to create single source barium titanate precursor with correct stoichiometry

SINGLE SOURCE PRECURSOR SYNTHESIS OF BARIUM TITANATE - FERROELECTRIC MATERIAL

• Ti(OBu)4(aq) + 4H2O Ti(OH)4(s) + 4BuOH(aq)

• Ti(OH)4(s) + C2O42-(aq) TiO(C2O4)(aq) + 2OH-(aq) + H2O

• Ba2+(aq) + C2O42-(aq) + TiO(C2O4)(aq) Ba[TiO(C2O4)2](s)

• Precipitate contains barium and titanium in correct ratio and at Precipitate contains barium and titanium in correct ratio and at 920920C decomposes to barium titanate according to:C decomposes to barium titanate according to:

• Ba[TiO(C2O4)2](s) BaTiO3(s) + 2CO(g) + 2CO2(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

Above 120Above 120C (TC (Tcc) - Cubic) - Cubic perovskite equivalent O-Ti-O bonds in BaTiO3

Below TBelow Tcc Tetragonal Tetragonal perovskite long-short axial O-Ti—O bonds induced aligned electric dipoles in BaTiO3

Cubic dielectric above Tc – paraelectric state - below Tc multi-domain state with cooperative electric dipole interactions within each domain – aligned in domain but randomly oriented between domains

Multidomain ferroelectric dipoles align in E field below Tc

Single domain superparaelectric

Note - small grains – complications - tetragonal to cubic surface gradients - ferroelectricity is particle size dependent and can be lost

Paraelectric a = 4.018Å Ferroelectric a = 3.997Å, c = 4.031ÅDisplacive Transition

Ti moves off center

HYSTERESIS OF POLARIZATION OF FERROELECTRIC BaTiO3 IN APPLIED FIELD E

Random domain dielectric Aligned domain ferroelectric

Single domain superparaelectric

Field E

P

E

Ps

Pr

Pc

Polarization Hysteresis Behavior P vs E Diagnostic of Ferroelectric

Ps saturation polarization

Pr remnant polarization

Ec coercive field

Synthesis of a Ferroelectric Random Access Memory (FeRAM) 0.5 Tbit/in2

Polarization Switching by Changing Direction of Applied Electric Field

DPN Direct Reaction Solid State Chemistry Synthesis of Ferroelectric PbTiO3 Array

Synthesis Precursor Sol

PbO + TiO2 PbO + TiO2 PbTiO3 PbTiO3

DPN Synthesis of PbTiO3 (PTO)• 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 Conducting AFM tip and substrate enable PFM and EFM ferroelectricity measurements on individual dots 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)5 LiNb(OEt)6 LiNbO3

• LiNb(OEt)6 + H2O LiNb(OEt)n(OH)6-n gel• LiNb(OEt)n(OH)6-n + + O2 LiNbO3

• 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’ + H2O• Yields glassy product • Sintering product in air - induces crystallization

INDIUM TIN OXIDE –ITO – CHANGED THE WORLD!

• Indium sesquioxide In2O3 (wide Eg semiconductor) electrical conductivity enhanced by n-doping with (10%) Sn(4+)

• ITO is SnnIn2-nO3

• 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 50-100C, heat at 350C in air to produce ITO

• Check electrical conductivity and optical transparency

Doping Basics on TCOs – The Big Three

• 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)

TCO Materials are NOTNOT that Simple

• 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

• In2-xSnxO3-2x • 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

= = ee + + hh• Reduces conductivity • Optimizing electrical conductivity of ITO by materials chemistry is not so simple

Nanocrystalline Antimony Doped Tin Dioxide - ncATO

A Nanomaterial that Could Change the World

How, Why, When !!! ???

Welcome to Beautiful ncATO

TCO’s• 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

A Little Nanochemistry Secret

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

Nanochemistry Synthesis of ncATO

• Non-aqueous sol-gel in C6H5CH2OH

• Benzyl Alcohol solvent and source of oxygen

• ROH + MCl MOH + RCl

• Or

• ROH + MOEt MOH + ROEt

• MOH + HOM MOM

ncATO

Benzolate Capping of ncATO

Why ncATO?

• 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

Meet ncATO • 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).

ncATO Diagnostics• 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

• Conductivity – nc size and nc dopant concentration and oxidation state dependence

ELECTRON BEAM LITHOGRAPHY

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 TiO2 Based Resists

LOCALIZED HEATING AT THE NANOMETER SCALE

Choosing the right solid state precursor to make resist

benzoyl acetone

tetrabutoxyorthotitanate

SUB -10 NM NANOSCALE DIRECT SOLID STATE REACTION

Electron Beam Nanolithography Using Spin-Coated TiO2 Resists

• Utilization of spin-coated sol gel based TiO2 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 >107 times more sensitive to an electron beam than sputtered TiO2 and crystalline TiO2 films.

Choosing the right solid state precursor

Sub-10 nm Electron Beam Nanolithography Using Spin-Coated TiO2 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.

• Such negative patterns can be written with a pitch as close as 30 nm.

Choosing the right solid state precursor

Nanometer scale precision structures

Nanoscale TiO2 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

How Good is EBL?

in solid state materials chemistry - shape, size and defects are everything! form, habit, morphology...

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