materials science p6_10.pdf
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Materials Science P6_10.pdfTRANSCRIPT
Physics in Materials Science
Roland V. Sarmago
DISCLAIMER: The images presented in the following slides are not mine! In the interest of educating young and eager minds, I have liberally gleamed these images from the web without intent to profit by it except to provide information. Due to the number of the images borrowed, it is not practical to list all sources. No part of this presentation should be commercially distributed.
Materials
Any object employed to achieve or address a particular purpose
-Wood for tables
-Metals for knives
-Air molecules to increase volume
-Silicon to control flow of electrons, etc
These objects are employed (application) by exploiting particular properties of the object
-Hard/soft, lustrous/dull, conductivity/insulation, malleability/stiffness, elastic/rigid
FUNCTION
APPLICATION
STRUCTURE
PROPERTIES
Let's take a metal as example
Hard Objects
Heavy
Can be bent and not break
Can be stretched
Can be shaped
Though
Can be brittle too
Good Conductors
HOW CAN A METAL BE ALL THESE?
How Physics gets into Materials Science
Physics also allowed us to see how these atoms are arranged in matter
All matter is composed of atoms
X-ray diffraction Pattern
Crystal Structure
Pure metal
Alloy (Mixture of two atoms)
crystalline polycrystalline amorphous
STRUCTURE → PROPERTIES
Structure is dictated by interactions
OTHER ATOMIC ARRANGEMENTS
nucleus
electrons
valence electrons
ELECTRONIC STRUCTURE → ELECTRONIC PROPERTIES
OTHER TYPES OF BONDING
Except for the nuclear arrangement, very difficult to see other structure
Energ
y
Distance from Nucleus 0
There is structure in the Energy
This is the usual tool in our chemistry class
Energy (Well) Diagram
These electrons are located “very deep” in the atom
These electrons can be found on the “outermost” part of the
atom
Deeper Level
Shallow Level
Energ
y
Distance from Nucleus 0
This represents how the electrons are clustered around an energy level
The red circles represent levels that are NOT occupied by electrons
OCCUPATION DIAGRAM FOR SINGLE ATOM
The wells are not really “FULL” of electrons
Energ
y
Distance from Nucleus 0
Energ
y
Distance from Nucleus 0
Lets take two similar atoms
Same Electronic Structure
Internuclear distance
The relative view from each atom
Electrons deep in the atom
Outer Electrons
These electrons retain their atomic characteristics
These electrons gain hybrid characteristics
If we bring the two atoms together the situation below will be realized
Nucleus 1 is here
Nucleus 2 is here
Energ
y
Hybrid Electron Levels
BAND STRUCTURE
If more atoms are added in the mix, the “energy space” occupied by black dots (electrons) gets filled and more red circles appear in the unoccupied “energy space”
More distinct structure appear
1. Splitting into Energy Bands 2. Appearance of “Energy Gaps” 3. Bands may be “FULL”, “EMPTY” or PARTIALLY OCCUPIED
ELECTRONS CANNOT BE IN THE GAPS
1 2 3
metal insulator semiconductor
When an electronic band is either completely full or completely empty, the material will be an insulator
When an electronic band is partially filled, the material will be a conductor.
By “filled”, we mean all possible states (or seats or spaces) are already occupied. If this were a movie house: ALL SEATS ARE TAKEN. If this were a parking lot: FULL PARKING.
empty = unoccupied
conductor
electrical conductivity is the motion of electron (charges) in the material
these are energy groupings
Electrons cannot make jumps within the occupied region (black) because the levels (seats) are occupied. The electrons must jump into the unoccupied region (red). This is CONDUCTION
insulator
Why doesn't an insulator conduct electricity?
deep energy level
shallow energy level
In order for the electrons to “move”, it must get into the unoccupied region (red). But it must first “climb out” of the occupied region (black) through the Gap. If the gap is small, it may be possible to jump using only a little energy. The material is a SEMICONDUCTOR
gap
If the gap is large, it will need a lot more energy to climb out of the occupied levels The material is an INSULATOR
gap
What is Materials Science?
It is the tweaking of the various structures of matter to achieve
/ get / arrive at desirable
properties.
What do we do at NIP?
We tweak semiconductors so they become
1. fast switches
2. good absorbers of sunlight
3. emitters of UV light
We tweak “bad” metals so they become good superconductors
Size is also a kind of structure. We make these materials smaller (nano-materials) to discover new, interesting properties.
THANK YOU VERY MUCH