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ELECTRONIC PROPERTIES OF MATERIALS

LECTURE ONE

GENERAL INTRODUCTION

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Aims This unit is designed to introduce the basic structure of electrical

materials

To lead to an understanding of electrical phenomena on materials

with a focus on electrical conduction in semiconductors, metals, and

dielectrics.

The magnetic response of solids is also explained to give students a

full picture.

Learning Outcomes

Knowledge and Understanding

Having successfully completed the module, the student will be able

to:

Understand charge behaviour in different materials

Classify the materials based on energy band theory

Select proper materials for different applications

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Intellectual Skills

Having successfully completed the module, you will be able to:

Able to describe how electrical charge moves through throughdifferent materials

Appreciate the importance of choice of materials in engineering

applications.

Course code: EEE 308Credits: 3 credit hours theory

Course instructor: Dr. Mohammad Al Hakim

Associate Professor, Room No: Academic 1106

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Text Book

Principles of electronic materials & devices

by S. O. Kassap.

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Topics Lectures

Elementary material science concepts: bonds, crystal types,

directions & planes

3

Electrical conduction in solids: Classical theory, Matthiessens rule,

resistivity, Hall effect etc.

3

Elementary quantum mechanics: Electron as a wave, Schrodingers

equation, infinite potential well, tunnelling etc

4

Band theory of solids: electrons in a band, effective mass, density of

states, energy band description of semiconductors.

4

Dielectric materials and insulation: material polarization, frequency

dependence, Debye equations etc

4

Magnetic properties of materials 3

Super conductivity 3

Tentative Schedule

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Attendance 5%

Class tests 10%

Lab 30%

Midterm I 15%Midterm II 15%

Final 25%

Marks distribution

Class tests: There will be 4 class tests

throughout the semester.

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Shell model: Bohr model (1913)

Nucleus: Protons & neutrons

Protons & neutrons held together by a force that is fundamental.

Short range usually less than 10-15

m.

Electrons orbiting around nucleus. Electron cloud.

The shell model of the atom in which electrons are confined to live

within certain shells and in sub-shells within shells

Atomic structure and atomic numbers

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Atomic structure and atomic numbers

Shell and sub shells defines whereabouts of electrons.

Labeled using two sets of integers n and l called principal and orbital

angular momentum quantum numbers.

Integer n and l have values n=1, 2, 3and l=0,

1n-1 and l

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Example of carbon atom with atomic number 6

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Some terms

Valence electrons?

Inert elements: sub-shell full of electrons. Dont react. Atoms do not

bond together.

Li 1s22s1: is it inert?

What is excited state?

Ionization energy? Na requires 5.1 eV to form Na+

(cation)

Electron affinity? 3.6 eV is released when Cl- is formed. Which one

is energetically favourable Cl or Cl- ion?

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Virial Theorem

Average kinetic energy is related to the average potential energy

KE ! 1

2PE

Total Average Energy

E ! PE KE

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Bonding and types of solids

Two atoms brought close-valence electrons interact

with each other and with positively charged nucleus.

Result of this interaction often forms bond.

Bond formation has to be energetically favourable after

mutually attractive and repulsive forces.

What is bond energy and bond length?

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(a) Force vs. interatomic separation

(b) Energy vs. interatomic separation

Energy phenomenon when atoms are close to each other

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A. Covalent bonding

Two atoms can form this type of bond by sharing valence

electrons thereby reducing overall system energy

STRONGNATURE OF THE BOND

Insoluble in most of the solution

Non-ductile

Brittle

As electrons are not free, typically less

conductive

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B. Metallic bonding

When metal atoms are brought together valence electrons get

free and forms electron gas----------DELOCALIZATION

NON_DIRECTIONALNATURE OF THE

BOND

Metal ions are able to move under force----

-DUCTILE

FREE ELECTRONS CANRAPIDLY

MOVE

Highly conductive

FREE ELECTRONS CAN CONTRIBUTE

ENERGYTRANSFER

Good thermal conductivity

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C. Ionic bonding (salt)

The formation of ionicbondbetweenNaand Cl atoms in NaCl. The attraction

Is due to coulombic forces.

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Strong,brittle material and high

melting temperature compared to

metals.

Most of them are soluble in polar

liquids.

No free electrons-so typically

insulator.

Compared to metals and covalently

bonded solids these have lower

thermal conductivity.

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D. Secondarybonding (Van dar waals)

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E. Mixed or polarbond (ionic covalentGaAs)