0-d, 1-d, 2-d structures (not a chapter in our book!) nano 101 introduction to nanotechnology 1
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0-D, 1-D, 2-D Structures(not a chapter in our book!)
NANO 101Introduction to Nanotechnology
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Overview
Top DownBottom Up
Chemistry!
Crystal Growth• 0-D particles• 1-D particles• 2-D films
Milling• Large size distribution• No control of shape• Impurities
Lithography
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Top-Down Approaches
• Milling– Broad size distribution (tens to hundreds of
nm)– Varied shape and geometry– Impurities and defects from milling
• Lithography– Also includes bottom up method
3https://sites.northwestern.edu/vanduyne/files/2012/10/2001_Haynes_4.pdf
Particle Requirements
• Uniform size
• Uniform morphology
• Uniform chemical composition and crystal structure
• Monodispersed
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Homogeneous Nucleation/
Supersaturated solution
G kT
ln C
Co
G = Gibbs free energyK = Boltzmann constantCo = equilibrium concentrationT = temperatureΩ = atomic volume
Two competing forces
• Surface energy• Volume energy
N&N Fig. 3.2 5
Nucleation and Growth Rates
N&N Fig. 3.4
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Hot Injection• A way to separate nucleation and growth:
– One ionic precursor is heated to ~ 300 C– Other precursor is a room temp and injected– Rapid nucleation occurs followed by
temperature drop and growth phase
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Hot Injection
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Growth of Nanoparticles
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Chem. Rev., 2014, 114 (15), pp 7610–7630
Making Nanoparticles
1. Nucleation
2. Diffusion from bulk to surface
3. Adsorption to surface
4. Irreversible incorporation onto surface
Diffusion
Growth
If the slowest step is diffusion uniform particles
If the slowest step is layer by layer growth non-uniform particles
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Favoring Diffusion-limited Growth
• Low concentrations– Large diffusion distance
• High solution viscosity
• Introduce diffusion barrier
• Change rate of chemical reactions– Reactants used – Catalysts
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Other Strategies:• Heat up method – in situ formation of
reactive precursors
• Slow addition of precursors – for RT growth
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0-D Nanostructures: Surface Area and Energy
Surface energy increases with surface area
• Large surface energy = instability• Driven to grow to reduce surface energy
C. Nutzenadel et al., Eur. Phys. J. D. 8, 245 (2000).
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Electrostatic StabilizationEstablish Surface Charge Density• Adsorption of ions/charged species
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“Capping”
Steric Stabilization
Anchored• Irreversible binding
Adsorbed• Random, weak
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What is on the surface?• Current area of research:
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Probing the surface of platinum nanoparticles with 13CO by solid-state NMR and IR spectroscopies
Nanoscale, 2014,6, 539-546
Example: Colloidal Gold• Comprehensive study on synthesis and
properties of colloidal gold published by Faraday (1857)
• Classic method– Precursor: dilute chlorauric acid (HAuCl4)
– Reducing agent: sodium citrate (NaC6H5O7)
– Reaction temperature: 100 °C– Product: stable, uniform, ~20 nm particles
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Colloidal Gold Particle Size
N&N Fig. 3.9
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Colloidal Gold Particle Size
N&N Fig. 3.9
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Synthesis of Metallic Nanoparticles
• Reduction of metal complexes in dilute solutions
• Precursors– Elemental metals, inorganic salts, metal
complexes
• Reduction agents• Stabilizers
– PVA– Sodium polyacrylate
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Other Methods• Brust Synthesis
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•Reverse Micelle
Influence of “Capping”• Addition of polymer stabilizer• Used on surface to prevent agglomeration• Affects growth by limiting growth site• May interact with solute, catalyst, solvent• Can affect morphology
N&N Fig. 3.13
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Growth of Pt Nanoparticles• Found that ligands can terminate growth
instead of change growth rate.
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Influence of Temperature
N&N Fig. 3.14 24
Influence of Concentration
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J. Phys. Chem. B, Vol. 108, No. 40, 2004
Influence of Time
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Rhodium nanocrystalsJ. Phys. Chem. C, Vol. 111, No. 16, 2007
Influence of pH
Initial pH of reaction can affect size
27SnO2 J. Phys. Chem. B, Vol. 108, No. 40, 2004
Formation of Nanoparticles in Solution
Advantages:
1. Stabilization from agglomeration
2. Extraction of nanoparticles from solvent
3. Surface modification and application
4. Mass production
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MBE Quantum Dots
• Self-assemble due to lattice mismatch29
http://www.nanowerk.com/nanotechnology-news/newsid=37518.phphttp://www.mbe.ethz.ch/index.php?id=mbe
How are these 0D?
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GaAs GaAs
In As
E
Formation of Nanoparticles on Substrates
• Advantages:– No ligands needed– Very stable– Ready for electronic application– Access different materials easily
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