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Controlling Nanocrystal Size and Shape: Quantum Effects in Material Properties

Explore the intriguing world of nanocrystals with a focus on size and shape control using a simple approach, revealing the quantum effects behind conventional material properties. Discover how atoms at the nanoscale define unique physical characteristics in materials like gold, iron, and water. Uncover the relationship between size, shape, and properties of nanocrystals, exemplified by cobalt nanocrystals. Dive into the realm of quantum size effects and energy quantization to understand the fundamental principles governing material behavior.

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Controlling Nanocrystal Size and Shape: Quantum Effects in Material Properties

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  1. Conventional Properties

  2. Quantum Size Effects • A chemist likes to keep track of material in grams or in moles, where a 1 mole = 6 x 1023 atoms • But how many atoms do you really need … • for gold to become gold-colored ? • for iron to become magnetic ? • for water to flow like a liquid ? 1 < ? < 6 x 1023

  3. Colloidal Nanocrystal Shape and Size Control: The Case of Cobalt Victor F. Puntes, * Kannan M. Krishnan, A. Paul Alivisatos We show that a relatively simple approach for controlling the colloidal synthesis of anisotropic cadmium selenide semiconductor nanorods can be extended to the size-controlled preparation of magnetic cobalt nanorods as well as spher- ically shaped nanocrystals. This approach helps define a minimum feature set needed to separately control the sizes and shapes of nanocrystals. The resulting cobalt nanocrystals produce interesting two- and three-dimensional super- structures, including ribbons of nanorods. Cobalt at the Nanoscale R EPORTS

  4. “Trapped” Electrons Copper at the Nanoscale 1 nanometer = 1 nm One Atom IBM Research, 1992

  5. giga mega kilo milli micro nano pico 1,000,000,000 1,000,000 1,000 1 0.001 0.000,001 0.000,000,001 0.000,000,000,001 distance to moon U.S.A. U.C.I. you and me pencil lead blood cell nanoscience smaller than atoms Factors of One Thousand meter meter meter meter meter meter meter meter meter = meter = meter = meter = meter = meter = meter = meter =

  6. 0.1 m 10 um = 0.00001 m 1 km = 1000 m 1 nm = 0.000000001 m 10 Mm = 10,000,000 m Size and Scale Factors of 10,000

  7. Conventional Properties

  8. NanoPeriodic Table – Under construction

  9. Quantum Size Effects • A chemist likes to keep track of material in grams or in “moles”, where a mole equals 6 x 1023 atoms • But how many atoms do you really need … • for gold to become gold-colored ? • for iron to become magnetic ? • for water to flow like a liquid ? 1 < ? < 6 x 1023

  10. What’s the Difference? Quantization “Quantized” Energy Levelsonly certain properties are allowed at each sizeDE = hf = hc/l

  11. Energy Quantization

  12. What’s the Difference? Quantization Only certain energies are allowed: DE = hf = hc/l, where l is a wavelength scale

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