0-D, 1-D, 2-D Structures (not a chapter in our book!) NANO 101 Introduction to Nanotechnology

Overview Bottom Up Top Down Chemistry! Milling Lithography Large size distribution No control of shape Impurities Crystal Growth 0-D particles 1-D particles 2-D films Lithography

Top-Down Approaches Milling Lithography Broad size distribution (tens to hundreds of nm) Varied shape and geometry Impurities and defects from milling Lithography Also includes bottom up method https://sites.northwestern.edu/vanduyne/files/2012/10/2001_Haynes_4.pdf

Particle Requirements Uniform size Uniform morphology Uniform chemical composition and crystal structure Monodispersed

Homogeneous Nucleation/ Supersaturated solution G = Gibbs free energy K = Boltzmann constant Co = equilibrium concentration T = temperature Ω = atomic volume Two competing forces Surface energy Volume energy N&N Fig. 3.2

Nucleation and Growth Rates N&N Fig. 3.4

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

Hot Injection

Growth of Nanoparticles Chem. Rev., 2014, 114 (15), pp 7610–7630

Making Nanoparticles Nucleation Diffusion from bulk to surface Adsorption to surface Irreversible incorporation onto surface Growth If the slowest step is diffusion  uniform particles If the slowest step is layer by layer growth  non-uniform particles

Favoring Diffusion-limited Growth Low concentrations Large diffusion distance High solution viscosity Introduce diffusion barrier Change rate of chemical reactions Reactants used Catalysts

Other Strategies: Heat up method – in situ formation of reactive precursors Slow addition of precursors – for RT growth

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).

Electrostatic Stabilization Establish Surface Charge Density Adsorption of ions/charged species - +

Steric Stabilization “Capping” Anchored Adsorbed Irreversible binding Random, weak

What is on the surface? Current area of research: 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

Colloidal Gold Particle Size N&N Fig. 3.9

Colloidal Gold Particle Size N&N Fig. 3.9

Synthesis of Metallic Nanoparticles Reduction of metal complexes in dilute solutions Precursors Elemental metals, inorganic salts, metal complexes Reduction agents Stabilizers PVA Sodium polyacrylate

Other Methods Brust Synthesis 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

Growth of Pt Nanoparticles Found that ligands can terminate growth instead of change growth rate.

Influence of Temperature N&N Fig. 3.14

Influence of Concentration J. Phys. Chem. B, Vol. 108, No. 40, 2004

Influence of Time Rhodium nanocrystals J. Phys. Chem. C, Vol. 111, No. 16, 2007

Influence of pH Initial pH of reaction can affect size SnO2 J. Phys. Chem. B, Vol. 108, No. 40, 2004

Formation of Nanoparticles in Solution Advantages: Stabilization from agglomeration Extraction of nanoparticles from solvent Surface modification and application Mass production

MBE Quantum Dots Self-assemble due to lattice mismatch http://www.nanowerk.com/nanotechnology-news/newsid=37518.php http://www.mbe.ethz.ch/index.php?id=mbe Self-assemble due to lattice mismatch

How are these 0D? GaAs GaAs In As E

Formation of Nanoparticles on Substrates Advantages: No ligands needed Very stable Ready for electronic application Access different materials easily