Bulk: Films or crystals, amorphous oratom.uwaterloo.ca/MNS/102/Lectures 2020/20_11_sv.pdf · Bulk:...
Transcript of Bulk: Films or crystals, amorphous oratom.uwaterloo.ca/MNS/102/Lectures 2020/20_11_sv.pdf · Bulk:...
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Bulk:
Films or crystals, amorphous or
polycrystaline or single‐crystalline•
2D: Quantum wells, superlattices,
Langmuir‐Blodgett films, membranes,
plus nanodiscs, nanorolls, nanowalls,…•
1D: Nanotubes, nanowires, nanorods,
nanobelts,…•
0D: Nano or quantum dots, colloids,
nanoparticles•
3D: Nanocrystals, nanocomposites,
cellular, porous materials, hybrids,
polymers. 11‐ 1
•
Cluster: Objects with up to ~50 units•
Colloid: Stable liquid phase
containing dispersed nanoparticles of
1‐1000 nm in size•
Nanoparticle: Generally 1‐100 nm,
with amorphous, aggregates of
crystallites or single crystalline•
Nanocrystal: A single‐crystal, nm in
size
Lecture 11 MNS 102: Techniques for Materials and Nano Sciences
•
Module 1: Materials Synthesis – Overview•
Solid‐state synthesis; Other methods
•
Strategies for making nanomaterials: Top‐down vs bottom‐up•
Bottom‐up methods
•
Hydrothermal and Sol‐gel syntheses•
Electrochemical deposition
•
Templates, seed‐layers, and catalysts
211‐
Materials Synthesis•
Solid‐State Synthesis
combines elements and/or compounds without the use
of solvents. Raw materials are mixed together, usually as a blend of powders,
and the reaction is initiated with heat. In cases where one of the raw
materials is volatile, the reaction is conducted under a positive pressure in a
sealed container or “bomb”. After the reaction is complete, the new product
with the desired composition is isolated, generally without any washing or
other purification steps.•
Wet‐Chemistry Synthesis combines elements and/or complex ions through
reaction in solution, as promoted by heat and pressure. The solvent is
removed after the reaction, and this will usually be followed by
a purification,
or washing, step. Any remaining solvent will be removed by a final drying step
using heat and/or vacuum to produce the product.•
Reactive Gas Processing is usually used to produce intermediate and/or final
products using reactive gas(es), with appropriate flow, pressure
and
temperature control.
11‐ 3How to “MAKE”
NANOmaterial?
Solid‐State Synthesis
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High temperature direct rxn –
diffusion limited•
Steps (“heat & beat”
or “shake & bake”):
> Choose precursors > weigh > mix > pelletize
> choose container: crucibles/boats – ceramic (Al2
O3
~ 1950C; ZrO2
/Y2
O3
~2000C) or precious metals (Ag~960C; Au~1063C; Pt~1770C; Ir~2450C); or sealed tubes (quartz or SiO2
, Au, Ag, Pt, Nb, Ta, Mo, W)
> heat at what T, heating program, in what atmosphere (air, O2
, Ar, N2
, H2
, CO, CO2
, other gas) > grind & analyse; go back to shake & beat if rxn incomplete
•
BUT: could be expensive; rxn incomplete, inhomogeneous products; may not get desired nanostructures11‐ 4
Vapour Condensation & Melt Quenching
11‐ 5Source: M. Muhammed, T. Taskalakos, J. Korean Ceramic Soc. 40 (2003) 1027.
•
Vapour Condensation: Thermal decomposition/reaction of precursors in a
low pressure flame + rapid cooling of the decomposed products in
a cool gas
or chilled substrate [e.g. Al2
O3, TiO2
, ZrO2
] •
Melt Quenching: Spray plasma over falling powders + melting + rapid
cooling in cold water.
Strategies for making NanomaterialsTop‐down [Macro‐engineering]•Mechanical attrition or slicing or ball
milling –
successive “cutting”
of a bulk
material to nano size; only mechanical
force is used > economical; large scale
production possible.
BUT: Defects/dislocations;
polydispersity; aggregate formation;
morphology control difficult•Lithographies [Optical, electron‐beam,
ion‐beam] – involves etching +
deposition + patterning, capable of
producing complex materials/systems
at will and reproducibly, and for OL
cost‐effectively.•Machining: micro to nanostructures
BUT: Expensive; not fast 11‐ 6Source: M. Muhammed, T. Taskalakos, J. Korean Ceramic Soc. 40 (2003) 1027.
Bottom‐up [Molecular engineering]•
Vapour‐phase, liquid‐phase, solid‐state reactions, plus mixed phase
(L‐S) reactions•
Molecular self‐assembly
•
Building blocks + Nano‐architectures from building blocks•
Less defects, more homogeneous, good size and shape control
11‐ 7
•
Precipitation/ wet chemical method/
soft chemical method
•
Reduction of metal salt/ solution method•
Hydrothermal/ solvothermal•
Thermolysis/ colloidal synthesis•
Flame synthesis•
Photochemical synthesis•
Liquid‐liquid interface•
Synthesis in structural media•
Sol‐gel method
Precipitation/ wet chemical method/ soft chemical method
Precipitation – see Chem 123 – use concept to make new particles & crystals
Wet chemistry – “beaker chemistry”
or rxns done in liquid phase, e.g. “Wet Chemistry
Route to Hydrophobic Blue Fluorescent Nanodiamond”, Mochalin, Gogotsi, JACS 131 (2009) 4594
http://pubs.acs.org/doi/pdf/10.1021/ja9004514
Soft chemistry –•“Chimie Douce”
rxns are conducted
under moderate conditions (< 500 ℃);•Topotactic = structural elements of reactants are preserved in products but with
compositional changes•Used to modify electronic structure of solid (doping), design metastable
compounds, prepare reactive and/or high‐surface area materials•Intercalation (ion insertion); de‐intercalation; dehydration; ion exchange•BUT: Need appropriate precursor; metastable products are unstable
11‐ 8
11‐ 9
•
Precipitation/ wet chemical method/ soft
chemical method
•
Reduction of metal salt/ solution
method
•
Hydrothermal/ solvothermal•
Thermolysis/ colloidal synthesis•
Flame synthesis•
Photochemical synthesis•
Liquid‐liquid interface•
Synthesis in structural media•
Sol‐gel method
Source: “Synthesis of silver nanoparticles by chemical reduction
method and their antibacterial activity”
Guzman et al. Int. J. Chem.
Biol. Eng. 2:3 (2009) 104.
Source: “Chemical synthesis of magnetic nanoparticles”
T Hyeon.
Chem. Comm. (2003) 927.
Arrested
Precipitation
Source: http://cdn.intechopen.com/pdfs/16801/InTech‐
Flame_synthesis_of_carbon_nanotubes.pdf
Hydrothermal/Solvothermal Synthesis
11‐ 10
•
“Hydrothermal”
first used by Sir Roderick
Murchison (1792‐1871) to describe water action
at elevated T and P in causing various rock and
mineral formation.
•
Chemical reactions
in a sealed heated solution
above ambient T and P. Hydro = solvent is
water vs solvo = solvent is not water, e.g.
GaCl3
+ Li3
N → GaN + 3LiCl in benzene, 280°C
•
Autoclave
or Bomb heated above BP in oven.
•
System is always at a non‐ideal
and non‐equilibrium state, while
solvent is at its near‐critical,
critical, or supercritical state.
•
Microporous crystals, superionic
conductors, metal oxides,
ceramics, zeolites, carbonaceous
materials, magnetic materials,
phosphers, plus nanoparticles,
gels, thin films, helical/chiral
structures.
11‐ 11
Advantages•Most material can be made soluble in a proper
solvent by heating and pressurizing the system
close to its critical point;•Significant improvement in the chemical activity
of the reactant, and in producing materials that
cannot be obtained via solid‐state reaction;•Products of intermediate state, metastable state
and specific phase may be easily produced >
novel products of metastable state and other
specific condensed state;•Easy and precise control of the size, shape
distribution, crystallinity of the final product
through adjusting the parameters such as
reaction T, time, solvent type, surfactant type,
precursor type;•Could produce materials with a low MP, or high
VP (that tend to go pyrolysis);•Easy, low‐cost route to produce new materials
Disadvantages•Expensive autoclaves;•Safety issues during the reaction;•Could not monitor and observe
the reaction.•Difficult to control morphology,
size, size distribution•Not for all materials
Mechanism•Usually follows a liquid nucleation
model;•Different from solid‐state reaction
mechanism in terms of diffusion of
atoms/ions among reactants•Enhanced solubility –
solubility of
water increases with T, but alkaline
solubility increases much greater
with T – high pH
11‐ 12Source: Ko et al. Nano Lett. 11 (2011) 666. “Nanoforest of Hydrothermally Grown Hierarchical
ZnO Nanowires for a High Efficiency Dye‐Sensitized Solar Cell”
Sol‐gel Synthesis
•
Sol‐gel process = formation of a network
through polycondensation reactions of a
molecular precursor in a liquid; excellent for
making hard‐to‐break (high‐temperature)
material at room or low temperature (with
light weight or low density, high
porosity/surface area).
•
Sol
= a stable dispersion of collodial particles
(amorphous or crystalline) or polymers in a
solvent [c.f. aerosol – same but in a gas];
interact by van der Waals forces or H bonds.
•
Gel
= a 3D continuous network that encloses a
liquid phase, where the network is formed by
agglomeration of colloidal particles (colloidal
gel) or particles that contain polymer sub‐
structure with aggregates of sub‐colloidal
particles (polymer gel); covalent interaction >
irreversible usually.
11‐ 13
•
Steps:
Mix colloid to form sol >
hydrolysis + condensation >
drying to make the desired final forms
Silica Gel
11‐ 14
Source: https://www.llnl.gov/str/May05/Satcher.html
Homework 2B: Watch the following 2 videos:
http://www.youtube.com/watch?v=VlWGIKCV_6khttp://www.youtube.com/watch?v=35IgXnXnA1YIn less than 1 page and in point form, identify
the strengths and weaknesses of the sol‐gel
method.
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Electrochemical Cell Design based on Si or ITO Electrode (used for nanoparticle deposition)
Outputs the graph
A
V
CERE
WE
•
WE-working electrode [Au/Si or H-
Si(100) or ITO electrode]
•
RE-reference electrode (Ag-AgCl electrode)
•
CE-counter electrode (Pt wire)
•
In a 3-electrode system, the current is passed between the WE and the CE supplied by the reduction reaction, e.g. Cu2+
+ 2e-
Cu(s)
•
WE is kept at constant potential wrt RE.
•
Deposition of metal occurs on the surface of the WE until the surface concentration of metallic ions is depleted.
16
Cu Nanocrystals: Diffusion‐limited Growth Mechanism
500 nm
(a)
1 µm
(c) (d)
500 nm
(b)
0 2 4 6 8 10-2.0-1.6-1.2-0.8-0.40.0
Pot
entia
l (V
)
Time (s) 500 nm
(a)
1 µm
(c) (d)
500 nm
(b)
0 2 4 6 8 10-2.0-1.6-1.2-0.8-0.40.0
Pot
entia
l (V
)
Time (s)
1 2 3 4 5 6 70.0
0.2
0.4
0.6
0.8
1.0
Instantaneous
Progressive
I2 /I m2
t/tm
0 2 4 6 8 10
0.40.81.21.62.0
I (m
A/c
m2 )
t (s)
22
2
/2564.1exp1/9542.1
mmm
ttttI
I
222
2
/3367.2exp1/2254.1
mmm
ttttI
I
Diffusion‐limited instantaneous growth mode effective in the overpotential
region
0.2 mA/cm2
100 nm PPY
UPP OPP
Electrochemical Deposition
11‐ 17
•
Used in electroplating technology for making thin films•
Based on the concept of Reduction‐Oxidation rxns at
the CAThode and ANode in an appropriate electrolyte –
an electrochemical cell, i.e. AN
OIL‐RIG CAT•
Easy control of size, shape, distribution by applied V, t,
electrolyte concentration, pH, conductivity•
Many scanning modes: Cyclic voltammetry (Current vs
Voltage); Potenstiostatic Amperometry –
Current vs
Time at a fixed V; plus many others•
Simple, flexible, inexpensive to set‐up, many variations
with both aqueous and non‐aqueous electrolytes, used
in different sensor and coating technologies•
BUT: need conductive substrates, e.g. ITO‐glass
(ITO=Indium Tin Oxide), doped silicon, metals such as
gold film, glassy carbon –
materials need “harvesting”
after deposition; not always uniform/homogeneous
Common Tricks in ALL
Syntheses •
Templates: Well‐defined voids in templates
(pores, channels, hallow spaces) are used to
restrict the growth region in order to
guide/develop the desired nanomaterial forms
and patterns (nano‐molding), e.g. AAO (Anodic
Aluminum Oxide) or viruses.•
Seed layers: Pre‐deposited layer used to
promote growth of nanostructures in desired
morphology, crystalline phases and orientations
or on hard‐to‐deposit substrates; often also
used as adhesion layers between two dissimilar
materials. •
Catalysts: Used to promote growth of specific
nanostructural materials, with and without
orientation/crystallographic alignments, e.g. Au
nanoparticles. Note different growth modes:
VLS vs VS.11‐ 18
Source: “Virus Particles as Templates for MaterialsSynthesis”
T. Douglas, M. Young. Adv. Mat. 11 (1999) 679.
11‐ 19
Homework 2C: Read the following review:“Template synthesis of nanostructured
materials”, Y. Liu, J. Goebl, Y. Yin, Chem. Soc. Rev. (2013),
http://pubs.rsc.org/en/content/articlelanding/2013/CS/C2CS35369E.
In less than 1 page and in point form, identify the strengths and weaknesses of the templating
technique.