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Title: IN%20SOLID%20STATE%20MATERIALS%20CHEMISTRY%20-%20SHAPE,%20SIZE%20AND%20DEFECTS%20ARE%20EVERYTHING!


1
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

2
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

3
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

4
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 Ficks law J -D(dc/dx)
  • J Flux of diffusing species (/cm2s)
  • D Diffusion coefficient (cm2/s)
  • (dc/dx) Concentration Gradient (/cm4)

5
MORE ASPECTS OF SOLID-SOLID REACTIONS
  • The average distance a diffusing species will
    travel ltxgt
  • ltxgt (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 Tammans Rule
  • Extensive reaction will not occur until T reaches
    at least 1/3 of the melting point of one or more
    of the reactants.

6
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 turn

7
SURFACE 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

8
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???

9
Thinking About A, d, x Particle Relations
Small d Large d Large SA/V Small SA/V Small
x Large x
10
EXTRA CONSIDERATIONS IN SOLID STATE SYNTHESIS
  • x(thickness planar layer) µ 1/A(contact area)
  • A(contact area) µ 1/d(particle size)
  • Thus particle sizes and surface area connected
  • Hence x µ 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!!!

11
MINIMIZING DIFFUSION LENGTHS ltxgt (2Dt)1/2 FOR
RAPID AND COMPLETE DIRECT REACTION BETWEEN SOLID
STATE MATERIALS AT LOWEST T
12
MINIMIZING DIFFUSION LENGTHS ltxgt (2Dt)1/2 FOR
RAPID AND COMPLETE DIRECT REACTION BETWEEN SOLID
STATE MATERIALS AT LOWEST T
13
SYNTHESIS OF COMPOSITION TUNABLE MONODISPERSE
ZnxCd1-xSe ALLOY NANOCRYSTALS ELECTRONIC BAND
GAP ENGINEERING
x controlled by size of core and corona more on
this later
14
MINIMIZING DIFFUSION LENGTHS ltxgt (2Dt)1/2 FOR
RAPID AND COMPLETE DIRECT REACTION BETWEEN SOLID
STATE MATERIALS AT LOWEST T
  • 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 REAGENTS
15
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
16
Metal Dichalcogenides MX2
  • 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

17
MINIMIZING DIFFUSION LENGTHS ltxgt (2Dt)1/2 FOR
RAPID AND COMPLETE DIRECT REACTION BETWEEN SOLID
STATE MATERIALS AT LOWEST T
Johnson superlattice reagent design (Ti-2Se)6(Nb
-2Se)6n Low T annealing reaction (TiSe2)6(NbS
e2)6n 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
NbSe2 is a superconductor !!!
AT LOW T THE SUPERLATTICE REAGENTS YIELD
SUPERLATTICE ARTIFICIAL CRYSTAL PRODUCT
18
Superlattice precursor sequence
6(Ti-2Se)-6(Nb-2Se) yields ternary modulated
superlattice composition (TiSe 2)6(NbSe 2)6n
with 62 well defined PXRD reflections good
exercise give it a try Confirms correlation
between precursor heterostructure sequence and
superlattice ordering of final product
19
MINIMIZING DIFFUSION LENGTHS ltxgt (2Dt)1/2 FOR
RAPID AND COMPLETE DIRECT REACTION BETWEEN SOLID
STATE MATERIALS AT LOWEST T
Johnson superlattice reagent design (Ti-2Se)6(Nb
-2Se)6n High T annealing reaction (Ti0.5Nb0.5S
e2)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
20
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.

21
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 ???

22
CORE-CORONA NANOCLUSTER PRECURSOR BASED
KIRKENDALL SYNTHESIS OF HOLLOW NANOCLUSTERS
  • 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

23
Oleic Acid C17H33CO2H
Arrested nucleation and growth of nanocrystals
use of surfactant, ligand, high temperature
solvent properties
24
CORE-CORONA NANOCLUSTER PRECURSOR BASED
KIRKENDALL SYNTHESIS OF HOLLOW NANOCLUSTERS
  • counter-diffusion of Co(3)/2e(-) and S(2-)
    across thickening shell
  • faster diffusion of Co(3) than S(2-) creates
    vacancies VCo 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

25
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 dont believe it !!!
26
Time evolution of a hollow Co2S3 nanocrystal
grown from a Co nanocrystal via the nanoscale
Kirkendall effect Science 2004, 304, 711
27
TURNING NANOSTRUCTURES INSIDE-OUT
  • Kirkendall effect - discovered in 1930s.
  • 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

28
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.

29
Time evolution of a hollow CoSe2 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
30
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
31
Magnetotactic bacteria vesicle templated
nucleation and growth of superparamagnetic
nanocrystal dipole chain
Communication and cooperative behaviour between
bacteria communities relevant to evolutionary
biology ???
I know my magnetic North !!!
32
Works for Hollow ZnAl2O4 Spinel Nanotubes!!!
33
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 nanodiode or transistor, drug storage and
    delivery vehicle ???

34
NANOSCALE PATTERNING OF SHAKE-AND-BAKE
SOLID-STATE CHEMISTRY
MINIMIZING DIFFUSION LENGTHS ltxgt (2Dt)1/2 FOR
RAPID AND COMPLETE DIRECT REACTION BETWEEN SOLID
STATE MATERIALS AT LOWEST T
Younan Xia
35
Tutorial - Surface Chemistry of Silica
36
Polydimethylsiloxane PDMS (H3C)3SiOSi(CH3)2OnS
i(CH3)3
n Si(CH3)2Cl2 n H2O ? Si(CH3)2On 2n HCl
Condensation polymerization synthesis of PDMS - a
very famous polymer elastomeric and hydrophobic
- lets make a micromold and do chemistry
37
PDMS MASTER FOR SOFT LITHOGRAPHY MICROCONTACT
PRINTING mCP
Whitesides
38
PDMS MASTER
Whitesides
  • 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.

39
NANOSCALE PATTERNING OF SHAKE-AND-BAKE
SOLID-STATE CHEMISTRY
Younan Xia
40
NANOSCALE PATTERNING OF SHAKE-AND-BAKE
SOLID-STATE CHEMISTRY
(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 mm2
in area and separated by 5 mm. (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
41
NANOSCALE PATTERNING OF SHAKE-AND-BAKE
SOLID-STATE CHEMISTRY
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.
12 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
42
BEYOND MICROCONTACT PRINTING 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
43
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
44
tin oxide
aluminum oxide
Nano gas sensor
Nano catalyst support
silicon oxide
calcined
Nano optical waveguide
45
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!!!
46
HOW GOOD???
55,000-pen array was used to 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 (10020) nm, a
height of 30 nm, and were spaced by 20 mm in the
x direction and 90 mm in the y direction
corresponding to the distances determined by the
array architecture.
47
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-and-error methods to the
    new solid state chemistry and a rational and
    systematic approach to synthesis of materials

48
THINKING ABOUT MIXING SOLID REAGENTS
  • Drying reagents MgO/Al2O3 200-800C, maximum SA
  • In situ decomposition of precursors at 600-800C
    MgCO3/Al(OH)3 ? MgO/Al2O3 ?MgAl2O4
  • Intimate mixing of precursor reagents
  • Homogenization of solid reactants using organic
    solvents, grinding, ball milling,
    ultra-sonification

49
THINKING ABOUT CONTAINER 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 temperatures
    needs to be carefully evaluated for each system
    know your solid state chemistry

50
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

51
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
  • Concept precursors to magnetic Spinels tunable
    magnetic recording media
  • Zn(CO2)2/Fe2(CO2)23/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)23 ? ZnFe2O4 4CO 4CO2
  • High degree of homogenization, smaller diffusion
    lengths, fast rate at lower reaction temperature

52
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

53
DOUBLE 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

54
Good way to make chromite Spinels, important
tunable magnetic materials juggling
electronic-magnetic properties of the A Oh and B
Td ions in the Spinel lattice
DOUBLE SALT PRECURSORS
  • 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

55
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 control
  • BaCO3(s) TiO2(s) ? BaTiO3(s)
  • Sol-gel reagents useful to create single source
    barium titanate precursor with correct
    stoichiometry

56
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) ?
    BaTiO(C2O4)2(s)
  • Precipitate contains barium and titanium in
    correct ratio and at 920?C decomposes to barium
    titanate according to
  • BaTiO(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

57
BASICS FERROELECTRIC BARIUM TITANATE
Paraelectric a 4.018Å
Ferroelectric a 3.997Å, c 4.031Å
Displacive Transition
Ti moves off center
Above 120?C (Tc) - Cubic perovskite equivalent
O-Ti-O bonds in BaTiO3
Below Tc Tetragonal perovskite long-short axial
O-TiO bonds induced aligned electric dipoles in
BaTiO3
Note - small grains complications - tetragonal
to cubic surface gradients - ferroelectricity is
particle size dependent and can be lost
Multidomain ferroelectric dipoles align in E
field below Tc
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
Single domain superparaelectric
58
HYSTERESIS OF POLARIZATION OF FERROELECTRIC
BaTiO3 IN APPLIED FIELD E
Field E
Random domain dielectric
Aligned domain ferroelectric
P
Ps saturation polarization Pr remnant
polarization Ec coercive field
Ps
Pr
Single domain superparaelectric
Pc
E
Polarization Hysteresis Behavior P vs E
Diagnostic of Ferroelectric
59
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 ? PbTiO3

60
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
EFM ferroelectricity measurements on individual
dots
61
DPN Size and Thickness Control of PbTiO3 Nanodots
62
DPN PbTiO3 Nanodots How Small Can You Go?
63
DPN Synthesis of FeRAM Characterization of
Ferroelectricity By Piezoelectric and Electric
Field Force Microscopy (PFM, EFM)
64
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 D 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 MOH ? MOM H2O
  • Yields glassy product
  • Sintering product in air - induces crystallization

65
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(OB
    u)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

66
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)

67
TCO Materials are NOT that Simple
  • Objective is to optimize optical transparency and
    electrical conductivity
  • ITO SnIn 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
    2xO(-II)
  • Effect is to reduces number of electron n-dopants
  • Reduces conductivity
  • Also some unwanted Sn(II) formed in synthesis
    introduces holes
  • s se sh
  • Reduces conductivity
  • Optimizing electrical conductivity of ITO by
    materials chemistry is not so simple

68
Nanocrystalline Antimony Doped Tin Dioxide -
ncATO
  • A Nanomaterial that Could Change the World
  • How, Why, When !!! ???

69
Welcome to Beautiful ncATO
70
TCOs
  • Optical transparency and electrical conductivity
    of TCOs 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

71
A Little Nanochemistry Secret
Benzyl Alcohol High T Solvent and Reactant Source
of Oxygen in Non-Aqueous SolGel Chemistry
72
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

73
Benzolate Capping of ncATO
74
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

75
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).

76
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

77
ELECTRON BEAM LITHOGRAPHY
Top Down NanoFabrication - High Spatial
Resolution Patterning at the Nanoscale Using
Energetic Short Wavelength Electron Beams
78
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
benzoyl acetone
tetrabutoxyorthotitanate
Choosing the right solid state precursor to make
resist
79
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 gt107 times more sensitive to an
    electron beam than sputtered TiO2 and crystalline
    TiO2 films.

Choosing the right solid state precursor
80
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
81
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
82
Nanometer scale tolerances
83
How Good is EBL?
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