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Nano materials

Nano materials. The Joys of quantum confinement. Physics 355. Where we’ve been. symmetry  bonding in solids  crystal structures and diffraction  band theory  metals  semiconductors  semiconductor devices  phonons  magnetism  superconductivity.

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Nano materials

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  1. Nano materials The Joys of quantum confinement Physics 355

  2. Where we’ve been symmetry  bonding in solids  crystal structures and diffraction  band theory  metals  semiconductors  semiconductor devices  phonons  magnetism  superconductivity

  3. The color of gold changes with sizes The goal of nanoscience is to find and understand how physical properties change with size. Why Nano Small things are different. Nanoscience would be boring if small things were just like big things. Luckily they are not. Graphite, for example, takes on interesting shapes if it is kept from becoming a big solid. graphite nanotube buckyball

  4. Let’s Look at three aspects of the nanoscale • Number of possible vibrational states, or electronic states, is greatly reduced. • Small structures have a large ratio of surface area to volume than macroscopic objects. • Ferromagnetism is different on the nanoscale than in the bulk.

  5. Quantum confinement In our previous work on phonons, we calculated phonon spectra for essentially a near infinite network of atoms. In reality, these systems are finite. We solve this problem by having periodic boundary conditions. Numerical (symbols) and analytical (lines) phonon dispersion curves in the first Brillouin zone of a monoatomic atomic chain with N = 16, m = 1, a = 1, and k = 1.

  6. Quantum confinement When the number of atoms is relatively small, the number of allowed states is reduced. Instead of having a quasi-continuum, we have a set of discrete states. These states are separated by significant energy amounts – this is the essence of quantum confinement. vacuum thin metal film of thickness d substrate For electrons in the thin film:

  7. Quantum confinement Infinite well solution: Better solution:

  8. Quantum confinement Quantum Dots The smallest energy for the formation of an electron-hole pair is Semiconductor quantum dots (QDs) possess size tunable fluorescence and absorption properties.

  9. surfaces and interfaces

  10. surfaces and interfaces In bulk ferromagnetic materials, the energy required to flip one magnetic moment is on the order of the exchange energy, kBTCurie. This is true for nano-particles as well. Surface Localized State:

  11. Magnetism on the nanoscale In bulk ferromagnetic materials, the energy required to flip one magnetic moment is on the order of the exchange energy, kBTCurie. This is true for nano-particles as well. Iron Nanoparticles

  12. Bloch walls The drawing shows a ferromagnetic material containing a 180o domain wall (center). On the left, the magnetic moments are aligned downward. The hypothetical wall structure is shown if the spins reverse direction over Na atomic distances In real materials, N: 40 to 104. The thickness is typically 0.5 m.

  13. Magnetism on the nanoscale Assuming no external field, the energy required to rotate the entire magnetic moment of a small particle is Unfortunately, we do not know Binside. But, it turns out that it is dependent on the shape of the particle and its order of magnitude is µ0M, so we make the approximation that

  14. Magnetic properties of iron nanoparticles coercivity is the magnetic-field strength necessary to demagnetize a ferromagnetic material that is magnetized to saturation. It is measured in A/m, or traditionally in Oersted. 1 Oe = 79.578 A/m

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