0-d, 1-d, 2-d structures (not a chapter in our book!) nano 101 introduction to nanotechnology 1

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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