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SYNTHESIS AND ASSEMBLY

Discover how nanoscale size affects electronic energy bands, surface area-volume ratio, and unique properties like optical behavior and melting points. Learn about top-down and bottom-up processes in nanoparticle synthesis and optical properties of nanocrystals. Explore core/shell QDs and gas-phase synthesis for innovative material design.

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SYNTHESIS AND ASSEMBLY

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  1. SYNTHESIS AND ASSEMBLY

  2. Size – Dependent Properties

  3. Electronic Energy Band

  4. Nanoscale = High Ratio of Surface Area to Volume Repeat 24 times For example, 5 cubic centimeters – about 1.7 cm per side – of material divided 24 times will produce 1 nanometer cubes and spread in a single layer could cover a football field Source: Clayton Teague, NNI

  5. Size – Dependent Properties • Nanoscale sizes can lead to different physical and chemical properties - Optical properties - Bandgap - Melting point - Surface reactivity • Even when such nanoparticles are consolidated into macroscale solids, new properties of bulk materials are possible. - Example: enhanced plasticity

  6. Melting Point The melting point of gold particles decreases dramatically as the particle size gets below 5 nm Source: Nanoscale Materials in Chemistry, Wiley, 2001

  7. Top-Down and Bottom-Up Processes

  8. Nanoparticle Synthesis

  9. Optical Properties Ordinary light excites all color quantum dots. (Any light source “bluer” than the dot of interest works.) Quantum dots change color with size because additional energy is required to “confine” the semiconductor excitation to a smaller volume. Source: Bala Manian, Quantum Dot Corp.

  10. Optical Properties Material band-gap determines the emission range; particle size tunes the emission within the range Nanocrystal quantum yields are as high as 80% Narrow, symmetric emission spectra minimize overlap of adjacent colors Source: Bala Manian, Quantum Dot Corp.

  11. Core/Shell Heterostructure QDs

  12. Gas Phase Synthesis

  13. Thin-Film Synthesis of QDs

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