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Solid State Synthesis
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Solid State Reactions
Film deposition
Sol-gel method
Crystal Growth
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Synthesis References
• A.R. West
"Solid State Chemistry and its Applications"
Chapter 2 – Preparative Methods
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"Solid-State Chemistry – Techniques"
Chapter 1 – Synthesis of Solid-State Materials
J.D. Corbett – book edited by A.K. Cheetham and P. Day
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"Preparation of Thin Films"
Joy George
This book has a nice succinct treatment of the various thin film deposition methods.
The following references discuss various aspects or methods in solid state synthesis in
greater detail.
Low Temperature & Precursor Techniques
• "Crystallization of Solid State Materials via Decomplexation of Soluble Complexes"
K.M. Doxsee, Chem. Mater. 10, 2610-2618 (1998).
• "Accelerating the kinetics of low-temperature inorganic syntheses"
R.Roy J. Solid State Chem. 111, 11-17 (1994).
• "Nonhydrolytic sol-gel routes to oxides"
A. Vioux, Chem. Mater. 9, 2292-2299 (1997).
Molten Salt Fluxes & Hydrothermal Synthesis
• "Turning down the heat: Design and mechanism in solid state synthesis"
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A. Stein, S. W. Keller, T.E. Mallouk, Science 259, 1558-1563 (1993).
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"Synthesis and characterization of a series of quaternary chalcogenides
BaLnMQ3 (Ln = rare earth, M = coinage metal, Q = Se or Te)"
Y.T. Yang, J.A. Ibers, J. Solid State Chem. 147, 366-371 (1999).
"Hydrothermal Synthesis of Transition metal oxides under mild conditions"
M.S. Whittingham, Current opinion in Solid State & Materials Science 1, 227232
Chimie Douce & Low Temperature Synthesis
• "Chimie Douce Approaches to the Synthesis of Metastable Oxide Materials"
J. Gopalakrishnan, Chem. Mater. 7, 1265-1275 (1995).
High Pressure Synthesis
• "High pressure synthesis of solids"
P.F. McMillan, Current Opinion in Solid State & Materials Science 4, 171-178
(1999)
• "High-Pressure Synthesis of Homologous Series of High Cricitcal
Temperature (Tc) Superconductors"
E. Takayama-Muromachi, Chem. Mater. 10, 2686-2698 (1998).
• "Preparative Methods in Solid State Chemistry"
J.B. Goodenough, J.A. Kafalas, J.M. Longo, (edited by P. Hagenmuller)
Academic Press, New York (1972).
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Classification of Solids
There are several forms solid state materials can adapt
Single Crystal
Preferred for characterization of structure and properties.
Polycrystalline Powder (Highly crystalline)
Used for characterization when single crystal cannot be easily
obtained, preferred for industrial production and certain
applications.
Polycrystalline Powder (Large Surface Area)
Desirable for further reactivity and certain applications such
as catalysis and electrode materials
Amorphous (Glass)
No long range translational order.
Thin Film
Widespread use in microelectronics, telecommunications,
optical applications, coatings, etc.
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Solid State Reactions
(1) Area of contact between reacting solids
- We want to use starting reagents with large surface area to
maximize the contact between reactants
Consider the numbers for a 1 cm3 volume of a reactant
• Edge Length = 1 cm
# of Crystallites = 1
Surface Area = 6 cm2
• Edge Length = 10 μm
# of Crystallites = 109
Surface Area = 6 x 103 cm2
• Edge Length = 100Å
# of Crystallites = 1018
Surface Area = 6 x 106 cm2
- Pelletize to encourage intimate contact between crystallites.
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Time (h)
Schematic reaction, by interdiffusion of
cations of single crystals of MgO and
Al2O3, (c) Thickness, x of MgAl2O3 product
layer as a function of temperature and
time. (Pettit, Randklev and Felton, 1966) 6
Different parts of the crystal have different
structures and different reactivities
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(2) The rate of diffusion
Two ways to increase the rate of diffusion
• Increase temperature
• Introduce defects by starting with reagents
that decompose prior to or during reaction,
such as carbonates or nitrates.
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(3) The rate of nucleation of the product
phase
• Maximize the rate of nucleation by using
reactants with crystal structures similar to
that of the product (topotactic and epitactic
reactions).
a topotactic transformation is characterized by internal
atomic displacements, which may include loss or gain of
material so that the initial and final lattices are in coherence.
epitaxy - The growth of the crystals of one mineral on the crystal
face of another mineral, such that the crystalline substrates of both
minerals have the same structural orientation.
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What are the consequences of high reaction
temperatures?
• It can be difficult to incorporate ions that readily form
volatile species (i.e. Ag+).
• It is not possible to access low temperature,
metastable (kinetically stabilized) products.
• High (cation) oxidation states are often unstable at high
temperature, due to the thermodynamics of the
following reaction:
2MOn (s) Æ 2MOn-1(s) + O2(g)
Due to the release of a gaseous product (O2), the products
are favored by entropy, and the entropy contribution to the
free energy become increasingly important as the
temperature increases.
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Steps in Conventional Solid State Synthesis
1). Select appropriate starting materials
a) Fine grain powders to maximize surface area
b) Reactive starting reagents are better than inert
c) Well defined compositions
2). Weigh out starting materials
3). Mix starting materials together
a) Agate mortar and pestle (organic solvent optional)
b) Ball Mill (Especially for large preps > 20g)
4). Pelletize
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Steps in Conventional Solid State Synthesis
(continued)
5). Select sample container
Reactivity, strength, cost, ductility are all important
a) Ceramic refractories (crucibles and boats)
Al2O3 1950 °C $30/(20 ml)
ZrO2/Y2O3 2000 °C $94/(10 ml)
b) Precious Metals (crucibles, boats and tubes)
Pt 1770 °C $500/(10 ml)
Au 1063 °C $340/(10 ml)
c) Sealed Tubes
SiO2- Quartz, Au, Ag, Pt
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6)Heat
a) Factors influencing choice of temperature for
volatilization
b) Initial heating cycle to lower temperature can help to
prevent spillage and volatilization
c) Atmosphere is also critical
Oxides (Oxidizing Conditions) – Air, O2, Low Temps
Oxides (Reducing Conditions) – H2/Ar, CO/CO2, High T
Nitrides – NH3 or Inert (N2, Ar, etc.)
Sulfides – H2S
Sealed tube reactions, Vacuum furnaces
7) Grind product and analyze (x-ray powder diffraction)
8) If reaction incomplete, return to step 4 and repeat.
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Example: the synthesis of Sr2CrTaO6
1) Possible starting reagents
Sr Metal – Hard to handle, prone to oxidation
SrO - Picks up CO2 & water, mp = 2430 °C
Sr(NO3)2 – mp = 570 °C, may pick up some water
SrCO3 – decomposes to SrO at 1370 °C
Ta Metal – mp = 2996 °C
Ta2O5 – mp = 1800 °C
Cr Metal – Hard to handle, prone to oxidation
Cr2O3 – mp = 2435 °C
Cr(NO3)3*nH2O – mp = 60 °C, composition inaccurate
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• To make 5.04 g of Sr2CrTaO6 (FW = 504.2 g/mol; 0.01
mol)
• complete the reaction:
4SrCO3 + Ta2O5 + Cr2O3 Æ 2Sr2CrTaO6 + 4CO2
• you need:
SrCO3 2.9526 g (0.02 mol)
Ta2O5 2.2095 g (0.005 mol)
Cr2O3 0.7600 g (0.005 mol)
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• Applying Tamman’s rule to each of the reagents:
SrCO3 ⇒ SrO 1370 °C (1643 K)
SrO mp = 2700 K ® 2/3 mp = 1527 °C
Ta2O5 mp = 2070 K ® 2/3 mp = 1107 °C
Cr2O3 mp = 2710 K ® 2/3 mp = 1532 °C
• Although you may get a complete reaction by heating
to 1150 °C, in practice there will still be a fair amount
of unreacted Cr2O3. Therefore, to obtain a complete
reaction it is best to heat to 1500-1600 °C.
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Precursor Routes
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Approach : Decrease diffusion distances through
intimate mixing of cations.
Advantages : Lower reaction temps, possibly
stabilize metastable phases, eliminate intermediate
impurity phases, produce products with small
crystallites/high surface area.
Disadvantages : Reagents are more difficult to
work with, can be hard to control exact
stoichiometry in certain cases, sometimes it is not
possible to find compatible reagents (for example
ions such as Ta5+ and Nb5+ immediately hydrolyze
and precipitate in aqueous solution).
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Precursor Routes (continued)
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Methods : With the exception of using mixed cation
reactants, all precursor routes involve the following
steps:
1. Mixing the starting reagents together in solution.
2. Removal of the solvent, leaving behind an
amorphous or nano-crystalline mixture of cations
and one or more of the following anions: acetate,
citrate, hydroxide, oxalate, alkoxide, etc.
3. Heat the resulting gel or powder to induce
reaction to the desired product.
The following case studies illustrate some
examples of actual syntheses carried out using
precursor routes.
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Coprecipitation Synthesis of ZnFe2O4
• Mix the oxalates of zinc and iron together in water in a
1:1 ratio. Heat to evaporate off the water. As the amount
of H2O decreases, a mixed Zn/Fe oxalate (probably
hydrated) precipitates out.
Fe2 ((COO) 2) 3 + Zn(COO) 2Æ Fe2Zn((COO) 2) 5*xH2O
• After most of the water is gone, the precipitate is filtered
and calcined at 1000 °C.
Fe2Zn((COO) 2) 5Æ ZnFe2O4 + 4CO + 4CO2
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Precursor Routes (continued)
• This method is easy and effective when it works. It is
not suitable when
Reactants of comparable water solubility cannot be
found. The precipitation rates of the reactants are
markedly different.
These limitations make this route unpractical for
many combinations of ions. Furthermore, accurate
stoichiometric ratios may not always be maintained.
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Molten Salt Fluxes
• Solubilize reactants → Enhance diffusion → Reduce
reaction temperature
• Synthesis in a solvent is the common approach to
synthesis of organic and organometallic compounds.
This approach is not extensively used in solid state
syntheses, because many inorganic solids are not
soluble in water or organic solvents. However, molten
salts turn out to be good solvents for many ioniccovalent extended solids.
• Often slow cooling of the melt is done to grow
crystals, however if the flux is water soluble and the
product is not then powders can also be made in this
way and separated from the excess flux by washing
with water.
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Molten Salt Fluxes (continued)
• Synthesis needs to be carried out at a temperature
where the flux is a liquid.
• Purity problems can arise, due to incorporation of the
molten salt ions in product. This can be overcome
either by using a salt containing cations and/or
anions which are also present in the desired product
(i.e. synthesis of Sr2AlTaO6 in a SrCl2 flux) , or by
using salts where the ions are of a much different
size than the ions in the desired product (i.e.
synthesis of PbZrO3 in a B2O3 flux).
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Example 1
• 4SrCO3 + Al2O3 + Ta2O5 ÆSr2AlTaO6 (SrCl2 flux,
900°C)
• Powder sample, wash away SrCl2 with weakly
acidic H2O
• Direct synthesis requires T > 1400°C and Sr2Ta2O7
impurities persist even at 1600° C
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Solid State Metathesis Reactions
A metathesis reaction between two salts merely
involves an exchange of anions, although in the
context we will use there can also be a redox
component. If the appropriate starting materials are
chosen, a highly exothermic reaction can be devised.
MoCl5 + 5/2 Na2S ÆMoS2 + 5NaCl + ½ S
The enthalpy of this reaction is ∆H = -213 kcal/mol
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Hydrothermal Synthesis
• Reaction takes place in superheated water, in a
closed reaction vessel called a hydrothermal bomb
(150 < T < 500 °C; 100 < P < 3000 kbar).
• Seed crystals and a temperature gradient can be
used for growing crystals
• Particularly common approach to synthesis of
zeolites
• Example :
6CaO + 6SiO2 Æ Ca6Si6O17(OH)2 (150-350 °C)
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Sol-gel process
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Intercalation
• Involves inserting ions into an existing structure, this
leads to a reduction (cations inserted) or an oxidation
(anions inserted) of the host.
• Typically carried out on layered materials (strong
covalent bonding within layers, weak van der Waals type
bonding between layers, i.e. graphite, clays,
dicalchogenides,).
• Performed via electrochemistry or via chemical reagents
as in the n-butyl Li technique.
Examples :
TiS2 + nBu-Li Æ LiTiS2
b-ZrNCl + Naph-Li Æ b-LixZrNCl
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Dehydration
• By removing water and/or hydroxide groups
from a compound, you can often perform
redox chemistry and maintain a structural
framework not accessible using
conventional synthesis approaches
• Examples :
Ti4O7(OH)2*nH2O Æ TiO2 (B) (500° C)
2KTi4O8(OH)*nH2O Æ K2Ti8O17 (500° C)
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Ion Exchange
• Exchange charge compensating, ionically
bonded cations (easiest for monovalent
cations)
• Examples :
LiNbWO6 + H3O + Æ HNbWO6 + Li+
KSbO3 + Na + Æ NaSbO3 + K +
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Film Formation
• Dip
Coating
• Spin Coating
• Vapor Deposition
• Chemical Vapor Deposition
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Chemical vapor deposition (CVD) is a chemical process for
depositing thin films of various materials. In a typical CVD
process, the substrate is exposed to one or more volatile
precursors, which react and/or decompose on the substrate surface
to produce the desired deposit. Frequently, volatile by-products
are also produced, which are removed by gas flow through the
reaction chamber.
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Types of CVD Processes
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Atmospheric Pressure Chemical Vapour Deposition (APCVD)
Low Pressure Chemical Vapour Deposition (LPCVD)
Metal-Organic Chemical Vapour Deposition (MOCVD)
Plasma Assisted Chemical Vapour Deposition (PACVD)
or Plasma Enhanced Chemical Vapour Deposition (PECVD)
Laser Chemical Vapour Deposition (LCVD)
Photochemical Vapour Deposition (PCVD)
Chemical Vapour Infiltration (CVI)
Chemical Beam Epitaxy (CBE)
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Film formation
(a)
(b)
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MOCVD to prepare METAL, METAL OXIDE,
NITRIDE and SULFIDE FILMS
Metal-organic CVD (MOCVD) - CVD processes based on
metal-organic precursors, such as Tantalum Ethoxide,
Ta(OC2H5)5, to create TaO, Tetra Dimethyl amino
Titanium (or TDMAT) to create TiN.
The philosophy behind this work is the discovery of:
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volatile organometallic precursors
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sometimes single source containing more than one of the
required elements
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that are pure enough
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and cleanly produce the required elements on a desired
substrate
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at as low a temperature as possible
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often epitaxially to minimize interfacial defects
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MOCVD PRECURSORS
A favorite ligand is the bulky 2,2',6,6'-tetramethyl-3,5heptanedionate, basically a bulky acac ligand (TMHD)
Y(TMHD)3 Tsub = 160oC, Ba(TMHD)2 Tsub = 70-190oC,
and Cu(TMHD)2 Tsub = 125oC are very useful
MOCVD precursors
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MOCVD to prepare METAL, METAL OXIDE,
NITRIDE and SULFIDE FILMS
• Best precursors for copper films used in microelectronics
are Cu(hfacac)2 (VP 0.25 Torr at 60oC) at 250-350oC, and
Cu(hfacac)PR3 (VP 0.1 Torr at 60oC) at 120-350oC
hfacac = hexafluoroacetylacetonate
• Rare earth doped semiconductor films make use of the
sterically crowded encapsulated (C5H4Me)3Nd and
(C5H4CMe3)3Nd can sublime at 110oC and 10-3 Torr
allowing them to be doped into III-V semiconductors, the
idea is to excite the sharp 4f-4f intra-shell luminescence of
the rare earth center optically and electrically via the host
semiconductor crystals, which is of interest in fiber optical
communication:
GaMe3 + AsH3 + (C5H4Me)3Nd ⇒ Nd:GaAs
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• Nitride films are important as they display unique properties
including metallic behavior, extreme hardness, very high melting
points, high chemical resistance
This has generated considerable interest in MOCVD precursors
to nitride films
Homoleptic dialkyamides and ammonia react at temperatures as
low as 200oC to afford excellent quality TiN films:
Ti(NMe2)4 + NH3 (200-450oC) ⇒ TiN + organics
• Sulfide films possess a wide range of fascinating solid state
properties and have been the focus of much MOCVD research.
Most prominent application is in the area of cathodes for thin film
lithium batteries.
Promising materials are TiS2 and MoS2
TiCl4(HSC6H11)2 (VP 1-2 Torr, 25oC, single source precursor,
~200oC) ⇒ TiS2 + 2HCl + 2C6H11Cl
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Ceramic Materials
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Ceramic parts made of
Si3N4
Thermal Insulating Ceramic Tiles
for space shuttle
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CVD to produce diamond at low pressure and around
1000oC
Single crystal synthetic diamonds (3000oC and 130
kbar from graphite) make excellent heat sinks for
semiconductors in device applications
Example of high thermal conductivity of diamond laser
diode heat drain (yellow diamond n-doped with N, blue
diamond p-doped with B), conductivity of diamond 4x
greater than copper or silver at RT (10-20 watts/cmoC)
By 1996, it was estimated that semiconductor applications
could take 60% of worldwide diamond thin film market,
other contenders for use of diamond film made by CVD
are coated tools (abrasion resistance), optical disk
coatings (protective coatings), lens and window coatings,
loudspeakers (sound distortion control), UV laser coatings
(reduces laser heating)
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Synthetic methods for making diamond films all employ
low pressure deposition of 1%CH4/H2 onto 1000oC
substrate
• Heated filament method uses a hot wire to decompose the
methane, 2200oC, produces atomic C/H, 50 Torr pressure
silica bell jar, diamond film deposited on 1000oC substrate
• Direct current plasma jet arc discharge focuses coating on
a small area of substrate and can be scanned across a
substrate
• Microwave plasma discharge is used for commercial
production of diamond films
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Highly Organized Carbon Nanotube by
Chemical Vapor Deposition
B. Q. Wei, R. Vajtai, Y. Jung, J. Ward, R. Zhang, G. Ramanath,
P. M. Ajayan
xylene + [Fe(C5H5)2]
with flowing argon to 100mTorr and heated
gradually to 800 °C
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Nano Materials
Nanotechnology comprises any technological
developments on the nanometer scale,
usually 0.1 to 100 nm.
Synthesis of Nano Materials
1. Chemical processes
2. Physical processes
<Ref>: Nanomaterials: Synthesis, Properties &
Applications, eds. A.S. Edelstein & R.C.
Cammarata
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Metal particle size effect
atom → clusters → bulk metallic particle
• geometry
• coordination number
• chemical properties
change a lot for
particles ≤ 55 atoms
~ 1 nm diameter
• Particle size effect, usually investigated in the
range of 10 ~ 50 Å in diameter.
• When > 40-50 Å, the crystals exhibit “bulk”
behavior
<ref> Adv. Catal. 36, 55 (1989)
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Lowering of melting point on
Nano-metal Particles
Size Effect on Melting Point
gold: 1063°C →
330°C (2nm)
silver: 960°C →
100°C (2nm)
boiling water
can melt silver
Goldstrin et al, Science
(1992)
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Electronic effect
Electronic effect only apparent for particles < 2nm
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Unit Cells In
Cubic Crystal Structures
simple cubic
Body-centered cubic
(primitive cubic) (bcc)
Face-centered cubic
(fcc)
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C9
C7
C8
C8
C7
C6
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Geometric effect
terrace
edge
corner
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# atoms along
the particle edge
Coordination #
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Particle Size Effect
body-center cubic (bcc)
Fe
N 2 + H 2 ⎯⎯→
NH 3
Dumestic et al.
Larger particles are more active than small
ones because their surface has a higher fraction of
7-coord. Fe atoms.
Spencer et al.
at 525℃, 200 atm
rate on (111):(100):(110)=418:25:1.
body center cubic (111) poses a large conc. of
C7.
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Monodispersed metal oxide particles
prepared from homogeneous solutions
Preparation routes :
1. Deprotonation of hydrated cations
2. Controlled release of precipitating anions
3. Thermal decomposition of metal complexes,
such as organometallic compounds
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Preparation and Properties of Monodispersed Colloidal
Particles of Lanthanide Compounds.
Langmuir, 4, (1988) 32
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Size distribution analysis : A comparison
of the histogram obtained by electron
microscopy with the distributions from light
scattering at two wavelengths (436 and
546 nm).
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Precipitation domain for solutions
containing Ce(S04)2 and H2SO4 aged
at 90 "C for 12 h.
Symbols designating different
kinds of particles: ○, spheres; □,
rods, , rods mixed with spheres;
, a very small amount of spheres; x,
no particle formation.
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Chemical processes for preparing nano-particles
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Nucleation and Growth of CdSe on ZnS Quantum Crystallite
Seeds, and Vice Versa, in Inverse Micelle Media
J. Am. Chem. SOC., 112 (1990) 1332
Figure 7. Bright field transmission electron micrograph
of (ZnS),-(CdSe),Ph particles. Particles showing lattice
images have ( 1 1 1 ) axes in the plane of the photograph.
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Preparation of ferrofluids
A. 2 FeCl3 + FeCl2 + 8 NH3 + 4 H2O → Fe3O4 (s) + 8 NH4Cl (aq)
B. Add cis-oleic acid [CH3(CH2)7CH=CH(CH2)7COOH ] in oil
C. Remove water
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A ferrofluid, influenced by a
magnet underneath.
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Electrorheological fluid – suspension of particles in a
liquid medium whose viscosity can be tuned by an applied
electric field
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• An ER fluid consists of fine polarizable particles
suspended in a fluid of lower dielectric constant.
• Typically such fluids are assembled with a continuous
hydrophobic liquid phase (e.g. silicone oil) containing
hydrophilic particles (e.g. zeolite).
• The density of the particles is matched as closely as
possible with that of the oil to ensure good dispersion
upon mixing of the ER fluid.
• An applied electric field aligns the dipoles of water
molecules trapped in particles, thus polarizing the
particles. Particle polarization changes their organization
in the fluid and causes changes in fluid rheological
properties.
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silicone oil -dimethylpolysiloxane hydrolyzate
zeolite - crystalline aluminosilicate with open structures
Type A
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Nano-particles in confined space
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X-Ray Powder Diffraction line-broadening technique
Scherrer’s equation
kλ
d=
β cosθ
mean diameter
of the crystallites
diffraction
angle
line-broadening
k: a constant, ~ 1
Dependent on shape, reflection
indices, and definition of d, β
λ: the radiation wavelength
for CuKα, λ=1.5487 Å
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Correction for instrumental broadening
β 2 = B2 − b2
standard with particle d > 1,000 Å
with diffraction line near the target line
the breadth of the diffraction line
If β define as β1/2, half-maximum line breadth
K ~ 0.9
0.9λ
d=
β 1 cos θ
2
If correcting for strain and instrumental broadening,
the min. particle diameter ~ 20 Å. Otherwise, ~ 50 Å
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TEM technique
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Physical processes for preparing nano-particles
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Differential Scanning Calorimetry (DSC)
φr
(b)
φr
φr (T)
T
熱流型圓盤狀 DSC 的(a)裝置：S= 樣品，R= 參比物，(1)金屬圓盤，(2)加熱爐，(3)
蓋子，(4)溫度感應器，(5)程溫控制器；(b)量測曲線，φr = - K·∆T。
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功率補償型 DSC 的(a)裝置：S= 樣品，R= 參比物，(1)加熱器，(2)溫度感應器；(b)
控制電流環路，φm = - K·∆Tcalibrated。
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DSC 曲線呈現的三種理想化的熱變化
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Nano-material fabrication
Lab Chip, 2005, 5, 492–500
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Top-down
Fig. 1 (a) Bulk-/film-machining;
(b) hybrid-method for patterning.
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Bottom-up
Fig. 5 (a) Simplified schematics of the self-assembly
peptide nanotubes (cylinder) in the membrane. (b)
schematic representation of nanotube–vesicle networks.
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phospholipid bilayer
Cell Membrane- Proteins inserted
into a phospholipid matrix
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Molecular Assembly and SelfAssembly: Molecular Nanoscience for
Future Technologies
FIGURE 1. Chemical structure of (A) the Buckminster carbon-fullerene
C60, (B) of Cu-tetra-[3,5 di-t-butylphenyl]-porphyrin (Cu-TBPP), and (C) of
chloro-[subphthalocyaninato]boron(III) (SubPc). The molecular diameters
are 1 nm, 1.3 nm, and 1.5 nm, respectively, and all three molecules have
large delocalized -systems that are responsible for the Van der Waals
attraction between the adsorbates and the substrates.
Ann. N.Y. Acad. Sci. 1006: 291–305 (2003).
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FIGURE 5. Self-intermixed monolayer phase, C60 and SubPc (see Fig. 1 A
and C) codeposited on Ag(111), intermix and form a strongly anisotropic
pattern. The C60s are adsorbed in a quasilinear arrangement, and the SubPcs
act as spacers between these C60 lines. Image size, 9.7 x 9.7 nm2; sample bias,
U = 1.9 V; tunneling current, I = 20 pA. On the right, the proposed model of
the registry on Ag(111) is shown. The positions of the C60 and SubPc
molecules and the orientations of the latter are depicted inside the unit cell.
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