• 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
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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
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