Materials Science and Engineering/Doctoral review questions/Daily Discussion Topics/January 5, 2008
(111) and (100) planes
editThe (111) plane is the lowest energy interface
(100) texture results from strain
- This plane is associated with the lowest Young modulus
If creating this interface by straining a material, apply thermal energy to allow the atoms to rearrange
Ohm's Law and Rectifying Behavior
editWhat causes deviation of ohmic behavior of a light bulb?
editIncrease in resistivity due to increase of temperature
Rectifying behavior of a junction
editChange of conductivity due to impurity content
editScattering results from introduction of impurities into metal
Impurities in semiconductor can increase the number of charge carriers
What is the effect of electromigration?
editElectromigration is the transport of material caused by the gradual movement of the ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms. The effect is important in applications where high direct current densities are used, such as in microelectronics and related structures. As the structure size in electronics such as integrated circuits (ICs) decreases, the practical significance of this effect increases.
Principles of statistical mechanics
editBoltzmann's Law
editBoltzmann's statistics provides a description of the spatial arrangement of molecules in a potential field (magnetic, electrical)
- up and down spins
Indistinguishable and Distinguishable Particles
edit- Indistinguishable particles: Boltzmann's statistics
- Distinguishable particles: Fermi-Dirac statistics
Heat Capacity
editContributions of each degree of freedom to energy
edit- per degree of freedom (per molecule)
- Vibrations
- per degree of freedom (per mole)
- when considering three dimensions
Total energy of a diatomic molecule
edit
- translational (x,y,z) freedom:
- vibrational freedom:
- rotational freedom:
Definition of heat capacity
editPer mole:
Heat capacity in a metal
editFive types of polarization
editOn application of an electric field, electron deviates from nucleus on a small time interval
In ionic materials, ions can move
Information Suggested to MEMORIZE
editMobilities of materials classes
edit- Metals ~ 10^8 S/m
- Semiconductors (doped) ~ 10^3
- Semiconductors (undoped) ~ 10^(-2)
- Holes in Si
- Electrons in Si
- Insulators ~ 10^(-14)
Young's Modulus of materials classes
edit- Metals ~ 100 GPa (10^11 Pa)
- Rubbers ~ 10 MPa (10^7 Pa)
Band gap of materials
edit- Si = 1.12 eV
- GaAs = 1.42 eV
- Ge = 0.7 eV
- Visible light = 1.77-3.10 eV
Structures of materials
edit- III-V compounds
- Wurtzite (combination HCP)
- Zinc blende (combination of FCC)
Density of State Derivations
editHigh-k materials
edit- Why are high k-materials needed?
- Homeworks may be a helpful resource
- Fabrication of high k materials
Moore's Law
edit- Resource: paper by Megan and George
Most significant problems of the silicon industry
edit- Resistance of interconnects
- Channel mobility will be very good
Modern channel width
edit- 45 nm gate: channel length
- 7 nm oxide thickness
- Reduce tunneling effects
BJT
edit- Draw structure
- How to improve upon the device?
- Significance of heterojunctions
Examples of Major Material Classes
edit- Indirect semiconductor: Si
- Direct semiconductor: GaAs
- Ferroelectric: BaTiO3
- Superconductor: YBaCuO3, Nb-Ti
- Antiferromagnetic: Cr, Mn
- Soft ferromagnetic (refrigerator doors): defect-free Fe-Ni (permalloy)
- Hard ferromagnetic (refrigerator magnets): defect-full BaFeOx, rare-earth compounds, Alnico
- Anisotropic ferromagnets: Fe (BCC, [100] easy direction), Ni (FCC, [111]), Co (HCP, [0001])
- Diamagnetic: C2 (no net spin)
- Paramagnetic: B2 (net spin)
- Magnetoresistance:
- High-K Dielectric: HfO2
- Low-K dielectric:
- Polymer: Polyethylene
- Miscible system:
- Immiscible system:
List Of "Must Know" Trick Questions
edit- Write down Fick's first and second laws, as generally as possible. What is the origin of these equations?
- What happens to metals (such as Na) under extremely high pressures?
- Why does the electrical conductivity suddenly increase in metals at very low temperatures?
- What is k in Bloch's Theorem?
- What is so unique about diamond?
- Why is the sky blue? Why are sunsets red?
- What is the fundamental flaw in the regular solution model?
- Why do we use effective mass, rather than just mass, for mobility of electrons in a metal?
- What happens to the bandgap of a material under hydrostatic pressure?