Materials Science P6_10.pdf

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