Lecture 1 - Introduction to Solid State Physics - University of Surrey

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Solid-state physics provides a description of how atoms bond to form solids ... Band structure theory (collective behaviour of atoms in a crystal, band gaps ...
Solid State Physics Professor Stephen Sweeney Advanced Technology Institute and Department of Physics

University of Surrey, Guildford, GU2 7XH, UK

[email protected]

Office: 12ATI01 (book appointments by email)

Solid State Physics - Lecture 1

Where does this fit in? Nuclear physics: fundamental particles, radioactivity, fission, nuclear reactions etc.

Atomic physics: energy levels, chemistry, spin-effects, spectroscopy etc.

Solid-state physics: crystal structures, conductors, insulators, semiconductors, thermal properties, strength of materials etc.

Solid State Physics - Lecture 1

Solid-State Physics • Solid-state physics provides a description of how atoms bond to form solids • It shows how microscopic effects give rise to macroscopic behaviour: • Thermal conductivity • Electrical conductivity

Source: PRB Germany

• Semiconductors and optical properties

Solid State Physics - Lecture 1

Course structure • Delivery :

39 hours of lectures and tutorial periods & laboratory based activities within level 2 lab. classes

• Assessment:

Coursework test (week 15, Jan/Feb 2011) [13% of mm] Examination (two papers in May/June 2011) [23% of mm]

• Suggested reading (the course will not follow any particular book): Rosenberg, The Solid State, Oxford Rudden & Wilson, Elements of Solid State Physics, Wiley Kittel, Introduction to Solid-State Physics, Wiley Blakemore, Solid State Physics, Cambridge Univ. Press Ashcroft & Mermin, Solid State Physics, Wiley

Solid State Physics - Lecture 1

Course Aims • Learn about basic concepts in Solid State Physics: - Crystal structure (types, terminology, real and reciprocal lattices, diffraction) - Lattice Dynamics (phonons, thermal conduction, heat capacity) - Thermal statistics, i.e. how to describe the energy of electrons in solids (Fermi-Dirac distributions, Fermi energy, density of states) - Free electron theory (electrical conduction) - Band structure theory (collective behaviour of atoms in a crystal, band gaps, metals, insulators, semiconductors) - Low dimensional systems (quantum wells, quantum dots, application in semiconductor devices such as light emitting diodes and lasers)

Solid State Physics - Lecture 1

Why is this important?

Silicon Silicon wafer Sand (mainly SiO2)

iPhone Laptop Sat Nav Toaster etc…

Processor chip Solid State Physics - Lecture 1

Progress

1cm

30nm

First transistor (1947)

Intel transistor (2009)

Solid State Physics - Lecture 1

States of Matter Solid: atoms are packed together in a rigid structure with shortor long-range order (more later). As the solid is heated up, the atoms oscillate around their equilibrium positions but retain a rigid structure.

Liquid: atoms are closely packed but do not form a rigid structure. As the liquid is heated up the atoms move around but without clear relation to one another.

Gas: atoms are located far away from each other (a much lower density than for a liquid or gas) with little interaction with each other. As the gas is heated up the atoms become more energetic, increasing the probability of collision. (also plasmas, but we won’t worry about those here…) Solid State Physics - Lecture 1

What is a Solid? Could be a bulk composite with weakly bonded constituents. The atomic arrangement is completely random. Such materials are relatively weak, and are poor thermal and electrical conductors (e.g. wood).

In amorphous solids there may be short range order between atoms but the atoms do not overall form a periodic structure. The atoms themselves are at equilibrium spacing (e.g. glasses) In crystalline solids the atoms form a periodic structure and there is long range order in the position of the atoms (e.g. metals, diamond, silicon etc.). More than 90% of solids form crystalline structures.

Solid State Physics - Lecture 1

Crystal Structures An ideal crystal is constructed from an infinite repetition of identical groups of atoms •

The group is known as the basis (this will contain one or more atoms)



The set of points on which the basis sits is called the lattice (a mathematical construction)

Solid State Physics - Lecture 1

Lattices & lattice translation vectors Lattice translation vectors describe how to move around a crystal

1 dimensional (1D) case

a

r

r’

r'  r  ua 2 dimensional (2D) case (where u is an integer)

a1

r'  r  u1a1  u2a 2

a2 Solid State Physics - Lecture 1

Lattices & lattice translation vectors 3 dimensional (3D) case

a1

r'  r  u1a1  u2a 2  u3a3

a2

a3 More generally, for n dimensions:

r'  r  n una n

All possible combinations of un define the lattice Lattice translation vectors an are primitive if there is no other cell of volume
1 atom Basis can in practice contain many atoms:

Silicon is fcc with 2 atom basis Two interpenetrating fcc structures is called the diamond structure

Diamond structure: 1 1 1  4 4 4

Co-ordinates of atoms in basis are 000 and 

This is often called a tetrahedral structure Q. Calculate the bond angle. Solid State Physics - Lecture 1

(109.5o)

Crystal basis with >1 atom Ionic structure (more on bonding later in the course): NaCl – based on fcc structure of Na+ and Cl- ions Q. What is the density of salt if the crystal has a lattice constant, a, of 563pm? (~2200kgm-3)

a Virus (e.g. flu) ~ basis contains ~107-109 atoms !

Solid State Physics - Lecture 1