chem584.nanoscalematerials - Nanoscale Materials...

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1 1 Nanoscale Materials Introduction to Nanoscale Science and Technology by Massimiliano Di Ventra (Editor), Stephane Evoy (Editor), James R. Heflin Jr. (Editor). Springer, 2004. Yin, Y.; Alivisatos, A. P., Nature 2005 , 437 , 664. 2 Nanoscale Materials Synthesis Two levels in nanostructured materials preparation: Synthesis of the building blocks. Construction of structured materials from building blocks top down (macro engineering): photolithograpy or bottom up (molecular engineering): molecular self-assembly, low dimensional materials (e.g., quantum dots, nanotubes and nanowires)
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2 3 • If a bulk metal is made thinner and thinner, until the electrons’ coherence length is les than the thickness, this is “2D quantum confinement.” • Next level is quantum wire (1 D). • Then quantum dot (0 D). Source: Nanoscale Materials in Chemistry, Wiley, 2001 3D 2D 1D 0D 4 3D 2D 1D 0D
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3 5 Building Blocks Of Nanostructured Materials Polymers, either in solution for coating thin films or as particles for construction Metal nanoparticles and nanowires Semiconductor nanospheres, rods, wires, tetrapods Carbon nanotubes Colloidal metal and semiconductor particles: same basic method. 1. Make solutions of soluble precursor chemical compounds. 2. By chemical reaction, produce the insoluble metal or semiconductor particles (duh). 3. Be tricky and stop at colloid stage rather than large ppt. 6 Stabilization of Colloids Fundamental problem: The thermodynamically stable state of metals, semiconductors, and polymers is bulk material, not colloidal particles. Stable colloidal dispersions require an interfacial stabilizer: either thermodynamically stabilize the surface energy, or kinetically prevent aggregation (e.g., surface charge or steric bulk). The stabilizer often is a surfactant, which is charged (usually), gives steric protection to the surface, and stabilizes the surface by coordination to surface metal atoms.
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4 7 • Cluster: A collection of units (atoms or reactive molecules) of up to ~50 units. • Colloids: A stable liquid phase containing particles in the 1-1000 nm range. A colloid particle is one such 1-1000 nm particle. • Nanoparticle A solid particle in the 1-100 nm range that could be non- crystalline, an aggregate of crystallites, or a single crystallite. • Nanocrystal A single crystal in the nanometer range Nano Terms 8 Nanoparticles Source: Nanoscale Materials in Chemistry, Wiley, 2001
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5 9 Nanoparticles Spherical iron nanocrystals J. Phys. Chem. 1996, 100 , 12142 10 Nanoparticles
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6 11 Nanoparticles: Size Dependent Properties • Delocalization of valence electrons can be on the order of nanoparticle size. Structure also changes with size. • This leads to size dependent physical and chemical properties: Optical properties Bandgap Melting point Specific heat Surface reactivity • Even for nanoparticles consolidated into “bulk” solids, new properties can result: enhanced plasticity nano-porosity shape selective reactivity 12 • For semiconductors such as ZnO, CdS, and Si, the bandgap
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This note was uploaded on 12/04/2011 for the course CHEM 584 taught by Professor Suslick,k during the Fall '08 term at University of Illinois, Urbana Champaign.

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chem584.nanoscalematerials - Nanoscale Materials...

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