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0-D Nanostructures (aka Nanoparticles or NPs)

0-D Nanostructures (aka Nanoparticles or NPs). Review: What is matter again?. Why do we REALLY care about matter? What are some qualities about materials we wish were better?. There are two basic ways you can make nanostructures…what do you suppose they are?. Top down vs. Bottom up….

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0-D Nanostructures (aka Nanoparticles or NPs)

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  1. 0-D Nanostructures (aka Nanoparticles or NPs)

  2. Review: What is matter again? Why do we REALLY care about matter? What are some qualities about materials we wish were better?

  3. There are two basic ways you can make nanostructures…what do you suppose they are?

  4. Top down vs. Bottom up… Top Down Bottom Up Milling Chemistry! Crystal Growth • 0-D particles • 1-D particles • 2-D films Quenching Lithography

  5. Top-Down Approaches • Milling (like a rock tumbler) It’s not that great… • Broad size distribution (tens to hundreds of nm) • Varied shape and geometry • Impurities and defects from milling • Repeated quenching (melting, re-solidifying, dissolving, evaporating) It’s not that great either… • Limited to materials with certain specific properties • Difficult to control particle size and shape • Lithography Much better!!

  6. Bottom-Up Approaches Thermodynamics (energetically driven to grow): 3 stages • Supersaturation • Nucleation • Growth Kinetics (You can limit their growth externally by…) • Limiting amount of precursors • Limiting space for growth

  7. You typically WANT… • Uniform size distribution • Uniform morphology • Uniform chemical composition and crystal structure • Monodispersed (NOT AGGLOMERATED!)

  8. Homogeneous Nucleation Supersaturated solution G = Gibbs free energy K = Boltzmann constant Co = equilibrium concentration T = temperature Ω = atomic volume • Two competing forces • Surface energy (destabilizing, as we learned) • Volume energy (this is stabilizing…as particles get larger, it’s happier)

  9. Nucleation Activity: Phenyl Salicylate! Demo: Sodium acetate!

  10. 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).

  11. - - - - - - - - - + + + + + + + + + + + + + + + + + + + + + + + + Electrostatic Stabilization Establish Surface Charge Density • Adsorption of ions/charged species • Dissociation of charged species on surface • Isomorphic substitution of ions • Accumulation or depletion of electrons at surface

  12. Steric Stabilization • Polymer • Solvent • Adsorbed • Random, weak • Anchored • Irreversible binding

  13. Metallic NPs

  14. Example: Colloidal Gold • Comprehensive study on synthesis and properties of colloidal gold published by Faraday (1857) • Classic method • Precursor: dilute chlorauric acid • Reducing agent: sodium citrate • Reaction temperature: 100 °C • Product: stable, uniform, ~20 nm particles Other methods use polymeric stabilizers also as a diffusion barrier

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