1. Materials Classification and Properties Metals, Ceramics, and Semiconductors
NANO 52
Foothill College

2. Properties of Materials
Physical
Mechanical
Chemical
Thermal
Electrical
Optical

3. Physical Properties Strength Ductility Melting point Glass transition
Density

4. Mechanical Properties
Stress – strain behavior
Strength
Tensile properties
Compression, shear, torsion
Deformation
Hardness

5. Chemical Properties Acid - base Reactivity Corrosion Oxidation
Passivation

6. Thermal Properties Heat conductance Heat capacity Thermal expansion
Annealing temperature
(Melting point, softening point)

7. Electrical Properties
Electrical conductivity
Electrical resistance/impedance

9. Metal Structure / Bonding
Metallic bonds
All metals are made up of a vast collection of ions that are held together by metallic bonds.
A metal atom has a positive nucleus with negative electrons outside of it.
In a solid, each atom loses the outermost electron, which takes part in bonding.
They form a lattice of regularly spaced positive ions. Each ion has no control over its bonding electron.

10. Examples of Ceramics Clay, Minerals, Salts and Oxides
Technical Ceramics can also be classified into three distinct material categories:
Oxides: Alumina, zirconia
Non-oxides: Carbides, borides, nitrides
Composites: Particulate reinforced, combinations of oxides and non-oxides.

11. Ionic Bonding in Ceramics
Ceramic materials are formed from ionic bonds within their constituent atoms, oxides and salts.
Ionic bonds are not nearly as ‘ductile’ as metals, causing ceramics to be brittle.

12. Metallic vs. Ionic Bonding
Much easier to deform materials with metallic than with ionic bonding. Why?
Sliding atom planes over each other (deformation) very unfavorable energetically in ionic solids!
 metals are ductile & ceramics (ionic) are brittle

13. Semiconductors

14. Semiconductors

15. Semiconductors
In solid state physics and related applied fields, the band gap is the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors.

16. Semiconductors
The ease with which electrons in a semiconductor can be excited from the valence band to the conduction band depends on the band gap between the bands, and it is the size of this energy bandgap that serves as an arbitrary dividing line (roughly 4 eV) between semiconductors and insulators.
Electrons excited to the conduction band also leave behind electron holes, or unoccupied states in the valence band. Both the conduction band electrons and the valence band holes contribute to electrical conductivity.
The holes themselves don't actually move, but a neighboring electron can move to fill the hole, leaving a hole at the place it has just come from, and in this way the holes appear to move, and the holes behave as if they were actual positively charged particles.