CHM 434F/1206F 2009
SOLID STATE MATERIALS CHEMISTRY
Geoffrey A. Ozin
Materials Chemistry and Nanochemistry Research Group, Chemistry
Department, 80 St. George Street, University of Toronto, Toronto,
Ontario, Canada M5S 3H6
Tel: 416 978 2082, Fax: 416 971 2011, Room: LM155
E-mail: gozin@chem.utoronto.ca
Group web-page: www.chem.toronto.edu/staff/GAO/group.html
Password: GoMaterials
CHM 434F/CHM 1206F
MATERIALS CHEMISTRY 2009
• Designed as follow-up to CHM 325, Polymer and Materials Chemistry,
which focused on synthesis-structure-property-function relations of
selected classes of low dimensional polymeric and inorganic materials.
• In this course we will be concerned with a comprehensive investigation
of a wide range of synthetic methods for preparing diverse classes of
inorganic materials and nanomaterials with properties that are
intentionally tailored for a particular use.
• The lecture notes begin with a primer that covers key aspects of the
background of solid-state materials, electronic band description of
solids, and connections between molecules and bonds in materials
chemistry and solids and bands in solid-state chemistry/physics.
CHM 434F/CHM 1206F
MATERIALS CHEMISTRY 2009
• Followed by a survey of archetype solids that have had a
dramatic influence on the materials world.
• Strategies for synthesizing and understanding the
formation of many different classes of materials and
nanomaterials with intentionally designed structures and
compositions, textures and morphologies, length scales
and dimensionality are then explored, emphasizing how to
control relations between structure and property and
ultimately function and utility.
• A number of contemporary issues in materials research are
critically evaluated to introduce the student to recent
highlights in the field of materials chemistry and
nanochemistry - emerging sub-disciplines of chemistry.
CHM 434F/CHM 1206F
MATERIALS CHEMISTRY 2009
• RECOMMENDED TEXT: L. Smart and E. Moore, Solid State
Chemistry, An Introduction, Chapman and Hall, London Third
Edition, L. Cademartiri, G. A. Ozin, Concepts in Nanochemistry,
Wiley-VCH, 2009.
• REFERENCE TEXTS: A. R. West, Solid State Chemistry and its
Applications, Wiley, 2009. D. W. Bruce, D. O’Hare, Inorganic
Materials, Second Edition, Wiley, 1997. L. V. Interrante, M. J.
Hampden-Smith, Chemistry of Advanced Materials, Wiley-VCH,
1998. C. N. R. Rao, J. Gopalakrishnan, New Directions in Solid State
Chemistry, Second Edition, Cambridge University Press, 1997. P.
Ball, Made to Measure, New Materials for the 21st Century, Princeton
University Press, 1997. G. A. Ozin, A. Arsenault, L. Cademartiri,
Nanochemistry: A Chemical Approach to Nanomaterials, Second
Edition, Royal Society of Chemistry, 2009.
COURSE EVALUATION 2009
• Mid-term test 90 min (25%)
• Written term paper 3000 words (15%)
• Written/oral assignments (20%)
• Final examination 180 min (40%)
SCHEDULE FOR TERM WORK
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Assignment 1: 1st October 2009 – bonding in materials (4%)
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Assignment 2: 8th October 2009 - short answer paper (8%)
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Assignment 3: 22nd October 2009, oral presentation - minisymposium, 6-9 pm, Davenport East (8%)
• Last day to drop course 3nd November 2009
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Assignment 4: 19th November 2009 - 90 minute mid-term test (25%)
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Assignment 5: 26th November 2009 - term paper 3000 words (15%)
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Assignment 6: Final exam 180 minute - December 2009 (40%)
Accessibility Needs
• The University of Toronto is committed to accessibility
• If you require accommodations for a disability, or have any
accessibility concerns about the course, the classroom or
course materials, please contact Accessibility Services as
soon as possible
• disability.services@utoronto.ca
• http://studentlife.utoronto.ca/accessibility
PRIMER: SOLID STATE MATERIALS CHEMISTRY
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Bonding in solids, ionic and covalent
Most solids are not purely ionic or covalent, polarization, dipolar,
dispersion, Van der Waals forces
Close packing concepts, hard spheres, coordination number,
substitutional-interstitial sites
Primitive unit cell, standard crystal systems (seven), lattices (fourteen
Bravais), translational and rotational symmetry (230 space groups)
Factors controlling structure, stoichiometry, stability (charge, size, spacefilling concepts) of solids
Basic concepts in bonding and electronic properties of solids
Defects, doping, non-stoichiometry, effect on properties
Electronic, optical, magnetic, charge-transport behavior of solids
BONDING AND ELECTRONIC PROPERTIES OF SOLIDS
CB
Eg
EF
EF
VB
W
Metal
Semiconductor
Insulator
Semimetal
Bloch-Wilson description of electron occupancy of
allowed energy bands for a classical metal,
semiconductor, insulator and semimetal.
ASSIGNMENT 1 – DUE 1st OCTOBER 2009
BONDING IN MATERIALS - SIMPLE OR COMPLEX?
IONIC
COVALENT
METALLIC
VDW
IONIC
COVALENT
METALLIC
VDW
NaCl
K3C60
K2Pt(CN)4Br0.3.2H2O (RNH3)2MnCl4
Si
(SN)x
C70
Cu
(TTF)2Br
C6H6
The bonding in these materials range from the simplest ones on the diagonal of the
matrix (single type of bonding) to more complex off-diagonal (mixtures of bonding).
Try to classify each of these in terms of structure-bonding-properties relations.
PRIMER: BLOCH-WILSON BAND DESCRIPTION OF SOLIDS
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Free electron traveling wave exp(ikx)
Electron l, wave vector k = 2p/l, p = h/l = (h/2p)k quasi-momentum
Description of electrons in solids
Modulated electron waves in a periodic crystal potential U(x)
Bloch orbitals (x) = exp(ikx)U(x)
Electron wavelengths from  to lattice spacing 2a
Scattering of e’s by nuclei, standing waves at Bragg condition nl = 2a
Gives rise to forbidden energy band gap, Eg, and VB and CB
First Brillouin zone runs from k = p/a
Band description in terms of density of states (DOS), n(E)
Density of occupied and unoccupied states, n(E) = fFD(E)N(E)
Fermi Dirac distribution of electrons fFD(E) = 1/(1 + exp(EF-E)/kBT)
EF chemical potential of metal essentially highest occupied level of VB
EF chemical potential of electrons, pinned for intrinsic SCs 1/2(Ev + Ec)
Electronic selection rules, optical transitions, momentum k, electric dipole m
Direct transitions, Dk = 0, kv = kc, conservation of momentum
Indirect transitions, Dk  0, kv + kph = kc, conservation of momentum
Doping, H impurity model, n/p-doping, radius and energies of electrons/holes
Effective mass of electrons/holes in solids, me,h* = (h/2p)2/(d2E/dk2)
PRIMER: BLOCH-WILSON BAND DESCRIPTION OF SOLIDS
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Tight binding description of bands k = 1nexp(ikna)n, periodic SALCAO Bloch orbitals
Essentially EHMO approximation for solids, Hii coulomb, Hij resonance integrals, yields E(k) vs k
dispersion plots
Useful relations, orbital overlap, band width, delocalization, band gap, band curvature, m*,
mobility, conductivity
Junctions between SCs, Guass’s theorem, contact potential, band bending
Semiconductor np-junction diodes, M-SC junctions, Schottky barriers/diodes, ohmic contacts
Photovoltaics, photodetectors
Semiconductor-liquid junctions
Solar cells and photoelectrochemical cells
Semiconductor pnp and npn-junction bipolar transistors, amplifiers, switches
Metal-oxide-semiconductor junction field effect transistor, MOS-FET
Semiconductor LEDs, lasers, detectors
Organic LEDs, FETs
Quantum confined semiconductors, sheets, wires, dots
Quantum superlattices
Quantum devices, electronic/optical switches, MQW lasers, SETs
Nanomaterials, nanoelectronics, nanophotonics, nanomachines, nanofuture
SOLID STATE MATERIALS CHEMISTRY MEETS
CONDENSED MATTER PHYSICS
OVERCOMING THE JARGON BARRIER!!!
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PHYSICS - SOLID STATE BAND
CHEMISTRY - MOLECULAR ORBITAL
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Valence band, VB, continuous
Conduction band, CB, continuous
Fermi energy, EF
Bloch orbital, localized/delocalized
Tight binding band calculation
n-doping
p-doping
Band gap, Eg
Direct band gap
Indirect band gap
Phonon, lattice vibration/libration
Peierls distortion, CDW
Polarons, magnons, plasmons
HOMO, discrete
LUMO, discrete
(Electro)chemical potential
Molecular orbital, localized/delocalized
EH molecular orbital calculation
Reduction, pH scale base
Oxidation, pH scale acid
HOMO-LUMO gap
Dipole allowed
Dipole forbidden
Molecular vibration/rotation
Jahn Teller distortion
No analogues in molecules
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ZrO2
ASSIGNMENT 2: Due 8th October 2009
Na1+xAl11O17+x/2
SOLIDS THAT INFLUENCED THE
alpha-SiO2
MATERIALS WORLD AND WHY?
C-Si
Give a brief 1-3 line descriptor for 20 of the materials in
a-Si:H
the list that illuminates the key features of each material
that were responsible for the impact that it had on the
alpha-AlPO4
high technology world of advanced materials
GaAs
Na56Al56Si136O384 This assignment is intended to get you reading around the
subject of solid state materials chemistry
(amine)xTaS2
It is very demanding to provide succinct answers to each
BaPb0.8Bi0.2O3
part of this question, it will take much reading and
SnFxO2-x
thinking
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YBa2Cu3O7-x
BaTiO3
LiNbO3
SrxLa1-xMnO3
LixCoO2
LaNi5
Nb3Ge
Ca10(PO4)6(OH)2
TiS2
ZnS
WC
(Si,Al)3(O,N)4
ASSIGNMENT 2
SOLIDS THAT INFLUENCED THE
MATERIALS WORLD AND WHY?
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h-BN
PbMo6Se8
Y3Al5O12
K2[Pt(CN)4]Br0.3
(CH)n
TTF(TCNQ)
c-C, h-C
C60
K3C60
SiOPc
MgB2
Porous Si
nc-Si
nc-TiO2
ASSIGNMENT 2
SOLIDS THAT INFLUENCED THE
MATERIALS WORLD AND WHY?
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(SN)x
HxWO3
WO3-x
CrxAl2-xO3
AgBr
Cu2HgI4
gamma-AgI
VO2
CrO2
AlxGa1-xPyAs1-y
SmCo5
Fe3O4
PEO(LiClO4)
ASSIGNMENT 2
SOLIDS THAT INFLUENCED THE
MATERIALS WORLD AND WHY?
ASSIGNMENT 3
CONTEMPORARY ISSUES IN MATERIALS CHEMISTRY
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MINI-SYMPOSIUM 22nd October 2009, 6-10 pm
ORAL PRESENTATION
MAXIMUM OF 3 TRANSPARENCIES
MAXIMUM 5 MINUTES
• First come first served – send your first three choices to
smamiche@chem.utoronto.ca
• Note that these questions will require considerable
background reading and thought and may not be able to
be addressed until well into the course
• Also this type of oral presentation is amongst the hardest
to prepare and most demanding in terms of successfully
delivering the main message
ASSIGNMENT 3: CONTEMPORARY ISSUES IN
MATERIALS CHEMISTRY, MINI-SYMPOSIUM
1. Why would the MoS2 faux fullerenes make ideal solid lubricants?
2. How and why would you use chemistry to make water flow uphill ?
3. How and why would you synthesize hexagonal mesoporous silica from a lyotropic
liquid crystal?
4. Why does nanocrystalline TiO2 enhance the RT Li+ ionic conductivity of the polymer
electrolyte PEO-LiClO4 in a solid state Li intercalation battery?
5. How and why would you solublize a single wall carbon nanotube?
6. How and why would you functionalize the tip of a single wall carbon nanotube?
7. How can an electroluminescent thin film device be made from monodispersed
surfactant-capped CdSe clusters?
8. How and why would you make thread from carbon nanotubes?
9. How and why might you synthesize a concrete spring?
10. How and why would you synthesize a zeolite-like material with a metal-organic
framework, called MOFs?
ASSIGNMENT 3: CONTEMPORARY ISSUES IN
MATERIALS CHEMISTRY, MINI-SYMPOSIUM
11. Why and how does the color and luminescence of monodispersed surfactant-capped CdSe
clusters change with the size of the clusters?
12. How would you make an abacus from C60?
13. How would you use a liquid crystal and a polymer to electrically control the
transmission of light through a glass window?
14. How would you use a liquid crystal to tune the optical Bragg reflection from a silica
colloidal crystal
15. How and why does the magnetotactic bacteria synthesize a chain of ferromagnetic
clusters?
16. How could you build a chemical sensor from monodispersed latex spheres?
17. How does the intermetallic LaNi5Hx function as a cathode in an alkaline-nickel hydroxide
battery?
18. How would you use a combinatorial materials chemistry approach to find a better lithium
solid state battery cathode or anode?
ASSIGNMENT 3: CONTEMPORARY ISSUES IN
MATERIALS CHEMISTRY, MINI-SYMPOSIUM
19. How can information be stored in CoCuCo metal magnetic multilayers?
20. How would you synthesize a plastic light emitting diode?
21. How and why would you synthesize a colloidal crystal with a diamond lattice of silica
microspheres
22. Why is a membrane made out of Nafion, a perfluorosulphonic acid, the solid
electrolyte-separator of choice in a hydrogen-oxygen fuel cell?
23. Why does the Tc of BiSrCuO type ceramic superconductors not change on intercalating a
5 nm thickness (cetylpyridinium)2HgI4 bilayer between the BiO layer-planes?
24. How can a single electron transistor be made from a single 5 nm diameter CdSe cluster?
25. How can a transistor be made from just one single walled carbon nanotube?
26. Why does the jewelers chisel preferentially cleave diamond along {111}?
27. Why does single crystal Si display chemical anisotropic etching in alkaline solutions that
is faster along {111} than {100}? What is this good for?
ASSIGNMENT 3: CONTEMPORARY ISSUES IN
MATERIALS CHEMISTRY, MINI-SYMPOSIUM
28. Why do green fluorescent 5 nm CdS nanoclusters blink?
29. Why does nitric acid preferentially open the end of a closed carbon nanotube?
30. Why are Fe, Co, Ni the only ferromagnetic transition metals?
31. Why does dye-sensitized nanocrystalline nc-TiO2 greatly enhance the light-toelectricity conversion efficiency of a photo-regenerative solar cell with the following
construction ITO|nc-TiO2, Ru(bipy)32+|I-, I2, CH3CN|Pt?
32. Why is the fracture toughness of the calcite nacre shell of the mollusk 1000x that of
calcite itself?
33. How and why would you tune the color of a colloidal crystal?
34. Nanotetrapods – new nanoscale building block new opportunities?
35. Carbon nanotubes or inorganic nanotubes – which way to go?
36. Chemically powered nanomotors – dream nanomachines or nanomachine dreams?
37. Bio-optics – nature did it first!
38. Laser holographic and direct laser written materials – what are they good for?
ASSIGNMENT 3: CONTEMPORARY ISSUES IN
MATERIALS CHEMISTRY, MINI-SYMPOSIUM
39. How does the anodic oxidation of a wafer of p-Si in aqueous HF, lead to self-limiting
monodispersed pore formation and a novel material that is photo- and
electroluminescent?
40. Using porous silicon how would you build an array of color tunable LEDs on a Si wafer
that could be used for a flat panel display?
41. How would you make an alumina or silicon thin disc with a hcp array of parallel nanoscale
channels starting with an aluminum disc or silicon wafer and then use it to make free
standing nanorod replicas comprised of Ag and Au barcode nanoscale segments
42. How would you synthesize Ca2C60? Assuming a fcc arrangement of C60 molecules and Ca
residing in octahedral interstices, explain why the material is semiconducting?
43. Given just a glass slide, curved lens, polarizers and cholesteryl esters, how would you make
a clinical thermometer with a precision of ± 0.1oC?
44. Which materials are in the battle for control of the flat panel display market and what
properties of the material will make it a winner?
45. How would you mimic biomineralization of magnetotactic bacteria in the laboratory to
synthesize better data storage materials?
46. How might you make a buckyball switch?
ASSIGNMENT 3: CONTEMPORARY ISSUES IN
MATERIALS CHEMISTRY, MINI-SYMPOSIUM
47. Given Pt, how would you devise a resistless lithography for Si wafers?
48. How would you synthesize and self-assemble semiconductor nanowires into
nanoscale devices like, lasers, LEDs, diodes, transistors, logic circuits? What
would it take to synthesize a better computer than current state of the art ones?
49. How could you self-assemble micron diameter silica spheres into a micron scale
checker board pattern?
50. Devise a way of synthesizing a micron scale checker board pattern of vertically
aligned zinc oxide nanowires – can you think of a use??
51. How could you store large amounts of information in a fcc colloidal crystal array
of microspheres?
52. How could you build a chemical sensor from monodispersed polymer spheres?
53. What are the materials options for the safe storage of hydrogen for fuel cell
powered cars?
54. Devise a way to synthesize a AuAg nanocluster inside a hollow AuAg nanosphere
55. Buckyball or Buckytubes – which one fuels the nanotechnology revolution?
56. How might you write the Lord’s prayer on the head of a gold pin?
57. Devise means of synthesizing quantum confined silicon in the form of nanoclusters,
nanowires and nanosheets and proving the existence in these nanostructures of
QSE in zero, one and two-dimensions.
ASSIGNMENT 3: CONTEMPORARY ISSUES IN
MATERIALS CHEMISTRY, MINI-SYMPOSIUM
58. Hello graphene – goodbye carbon nanotubes – fact or fiction?
59. How and why would you synthesize a superconducting MgB2 nanospring?
60. How and why would you synthesize silicon diatoms?
61. Evaluate the technological potential of materials chemistry that founded Opalux Inc
62. Which class of materials can slow the velocity of light to zero and how would you use this
property to build a better solar cell?
63. Gold nanorods cure cancer – fact or fiction?
64. Chalcogels – beyond silica gels?
65. Light emitting electrochemical cells – what are they and do they have a future?
66. How would you make a photonic nose from a nanoparticle-based 1D photonic crystal?
67. Dream up materials synthesis methods for making an antireflection coating
68. Nanodiamonds are a girls best friend?
69. Saving the incandescent lamp – why bother?
70. How would you make silicon solar cells more efficient?
71. Materials competing with silicon – dethroning the king of solar cells!
72. Chemically powered nanomotors – dream nanomachines or nanomachine dreams?
73. How would you make a radio from a single carbon nanotube?
74. Starting with a silicon wafer how would you make a single atom sensitive mass balance?
75. How and why would you make a nanodrum from graphene?
ASSIGNMENT 5: INDEPENDENT WRITTEN
PROJECT: SUGGESTED TOPICS
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First come first served – send your first three choices to
smamiche@chem.utoronto.ca
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Focus your attention on materials design, synthesis, characterization,
structure, property and function relations and the relevance of the
materials to advanced technologies
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High marks for this assignment will require more than just a written
representation of what you find in books, reviews and papers - it will also
require some evidence of creative ideas, original thinking and critical
commentary – make sure you keep a materials chemistry/science focus and
not too heavy on solid state physics or engineering
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A typed version is required of not more than 3000 words, not including
figures and tables.
• Hand in a bound copy to Professor Geoffrey A. Ozin by
26th Nov 2009
ASSIGNMENT 5: INDEPENDENT WRITTEN
PROJECT: SUGGESTED TOPICS
1. Evoking light emission from silicon - LEDs and lasers made of silicon - science fiction or reality?
2. Endohedral and exohedral fullerenes - what are they good for?
3. Inorganic polymers - materials for the next century?
4. Non-oxide open-framework materials - past, present and do they have a future?
5. Materials harder than diamond - can they be made and why do we need them?
6. Supramolecular templating of mesostructured inorganics - a solution looking for a problem?
7. Plastic electronics for the next millennium- goodbye silicon?
8. Carbon nanotubes - better than Buckminsterfullerene C60?
9. Capped semiconductor nanoclusters - what are they good for?
10. Capped gold nanoclusters - would Faraday be impressed?
11. Electrides - chemistry with the electron – past, present and do they have a future?
12. Magic of magnetic multilayers - giant magnetoresistance data storage materials - can they compete?
13. Molecular magnetism - a basis for new materials?
14. Photorefractive materials - do they have a bright future?.
15. Nanoscale patterning and imaging with scanning probe microscopes - smaller, faster, better?
16. High Tc superconductors - will they ever reach RT?
17. Kinetics of intercalation - getting between the sheets as fast as possible - why do we need to do this?
18. Layer-by-layer electrostatic self-assembly – designer thin films?
ASSIGNMENT 5: INDEPENDENT WRITTEN
PROJECT: SUGGESTED TOPICS
19. Alkane thiol self-assembled monolayers (SAMs) - what are they good for?
20. Biomimetic inorganic materials chemistry - why steal Nature’s best ideas?
21. Microgravity chemistry - why grow inorganic crystals in space?
22. Information storage materials - how dense can you get?
23. Microelectrochemical transistors and diodes - materials chemistry on a chip that did not make it?
24. Photonic band gap materials for a photonics revolution - trapping light - a new religion?.
25. Dye sensitized nanocrystalline semiconductors - high efficiency low cost solar cells – how are we doing?
26. Fuel cell materials - future of the electric vehicle - science fiction or reality?
27. Smart window materials - energy conservation and privacy - how do they work?
28. Forbidden symmetry - quasi-crystals for quasi-technologies?
29. Nanomaterials - will they really impact science and technology?
31. Silica film must be at least 4-5 atoms thick to be an insulator - end of the road for silicon electronics?
32. MEMS to NEMS – micro(nano)electromechanical machines - can they really do big things?
33. Nanowire nanocomputer - science fiction or reality?
34. On-chip lithium solid state microbatteries - towards on board power?
35. Nanosafety - a hot button scientific and political issue?
36. Materials self-assembly over “all” length scales – a panoscopic view of materials?
37. Electrophoretic, electrochromic, electrodewettable materials – battle for electronic paper?
ASSIGNMENT 5: INDEPENDENT WRITTEN
PROJECT: SUGGESTED TOPICS
38. Slow photons in photonic crystals - are they good for chemistry?
39. Barcode nanorods - do they have a future in bio-nanotechnology?
40. Dynamic self-assembly - towards complex systems in chemistry, physics and biology?
41. Periodic mesoporous organosilicas - new generation low k microelectronic packaging?
42. Molecular electronics - a problem without a solution?
43. Spintronics - can we really compute with electron spin rather than charge?
44. How would you write all the information in the library of congress on the head of a pin using a
chemistry approach - was Richard Feynman right?
45. Nanotetrapods – building blocks for future nanotechnology?
46. Chemically powered nanomotors – dream nanomachines or nanomachine dreams?
47. Carbon nanotubes or inorganic nanotubes – seeing the light at the end of the nanotunnel?
48. Nano: Top-down or bottom-up or an integration of both – which way to go?
49. The race for the hydrogen storage material – challenge for materials chemistry!
50. Bio-optics – helping the photonics revolution?
51. Binary nanocluster superlattices – a new periodic table of superatoms?
52. Elastic photonic crystals –stretching science and technology to new limits?
53. Luminescent nanoclusters - throwing light on living cells?
54. Mesoporous carbons – better lithium solid state battery anodes – pores for thought?
ASSIGNMENT 5: INDEPENDENT WRITTEN
PROJECT: SUGGESTED TOPICS
55. Hello graphene – goodbye carbon nanotubes?
56. How and why would you synthesize a superconducting nanospring made of MgB 2?
57. How and why would you synthesize silicon diatoms?
58. Evaluate the technological potential of the materials chemistry that founded Opalux Inc
59. Which class of materials can slow the velocity of light to zero and how would you use this property
to build a better solar cell or better photocatalyst?
60. Gold nanorods cure for cancer – fact or fiction?
61. Chalcogels – beyond silica gels?
62. Light emitting electrochemical cells – what are they and do they have a future?
63. Chemically smart Bragg mirrors – what are they good for?
64. How did the bio-optics of the mosquito eye enable a biomimetic synthesis of antifogging coatings?
65. Ultrathin nanowires – why are they special?
66. Piezochromic materials – pushy color?
67. Purifying carbon nanotubes – why is this important?
68. Thermoelectrics – solid state refrigeration to power generation materials
69. White light emitting diodes – death of the incandescent and fluorescent lamps?
70. Drug storage and targeted delivery materials
71. Magnetohypothermia materials – goodbye cancer?
72. MOFs, COFs, ZIFs – hydrogen storage materials – going beyond the acronyms
73. Making silicon solar cells more efficient
74. Materials competing with silicon – dethroning the king of solar cells!
75. Chemically powered nanomotors – dream nanomachines or nanomachine dreams?
76. How would you synthesize a laser based on a nanocrystal of gold?
77. How would you make a color tunable ink from magnetic nanoparticles?