Materials Science and Engineering Notes

Materials Engineering

  • Deals with designing, processing, testing, and discovering materials, mainly solids.
  • Focuses on:
    • Structure
    • Properties
    • Performance
    • Processing

Careers

  • Example: Designing cars to absorb energy from crashes using the right materials (harder metals).

Superconductors

  • Exhibit no electrical resistance.
  • Do not give off heat or other forms of energy.
  • Applications:
    • High-speed digital circuits
    • Particle detectors

Material Coatings

  • Coatings can alter material properties.

Failure Analysis

  • Example: Analyzing a landing gear failure to understand:
    • Where the crack originated from.
    • How it propagated.
    • Landing gear is designed to fail in a specific manner to prevent snapping.

Main Classes of Materials

  1. Metals
  2. Ceramics
  3. Polymers / Plastics
  4. Composites

Natural Hydrophobicity

  • Some materials naturally repel water.

Nano-Engineered Surfaces

  • Surfaces can be engineered at the nanoscale to be either hydrophobic or hydrophilic.
  • Scale: 1mm

Minimizing Light Reflection

  • Inspiration from butterfly eyes.
  • Moth-eye corneal nipple array structure.
  • Reference: D.G Stavenga, S Foletti, G Palasantzas, and K arikawa, Proc Biol Sci. 273(1587) (2006) 661–667

Photon Management

  • Using nanostructures like thin films, nanowires, and nanocones.
  • Dimensions: 500nm
  • Absorption rates vary based on structure. The graph shows:
    *Thin film
    *Nanowire
    *Nanocone
  • Result: A 25% increase in efficiency.
  • Reference: Jia Zhu etal. Mat. Sci. Eng R 2010.

Light Absorption and Emission in Semiconductors

  • Energy diagram:
    • E_c: Conduction band energy
    • E_v: Valence band energy
    • h
      u: Photon energy
    • k: wave vector

Quantum Confinement

  • Quantum confinement (depending on the size and shape of particles) radically modifies the light absorption characteristics for the same material.
  • Nanoparticles of the same material in suspension can have radically different absorption characteristics.
  • Reference: http://jessy.baker.googlepages.com/ucberkeley

Cadmium Selenide (CdSe) Nanoparticle Luminescence

  • Luminescence varies with particle size:
    • 1.2 nm
    • 1.5 nm
    • 2.1 nm
    • 50 nm

Graphite and Diamond

  • Diamond carbon: Carbon crystallized in a diamond cubic structure.
  • Face-centered cubic (FCC) unit cell with carbon atoms at lattice points.

Graphite Structure

  • Dimensions:
    • a = 1.42 Å
    • c = 6.71 Å
    • c/2 = 3.35 Å

Fullerene C60

  • A spherical molecule composed of 60 carbon atoms.

Carbon Nanotubes (CNT)

  • Crystalline structures of carbon:
    • Graphite
    • Graphene sheets rolled up to form nanotubes.