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ST03 – Electronics – particle level: structure of matter

Electronics – particle level: structure of matter

Lecturer:Smilen Dimitrov

Sensors Technology – MED4

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ST03 – Electronics – particle level: structure of matter

Introduction

• The model that we introduced for ST

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ST03 – Electronics – particle level: structure of matter

Introduction

• Goal – start with focus on electronics• To repeat about the atomic structure of matter, and the role of the

electron To discuss the difference between free and bound electron, and look at the corresponding visualization

• To discuss the photoelectric effect as a basic sensing process• To gain a starting insight into the structure of metals – important

as conductors in electrical circuits

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ST03 – Electronics – particle level: structure of matter

Structure of matter

• Matter – built up of molecules -> atoms -> nucleus and electron shell

• Electron as mathematical or physical point• Electrostatic forces: binding and free electron• Atomic models throughout history

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ST03 – Electronics – particle level: structure of matter

Historical timeline of the atomic model

• Democritus• Billiard ball model (Dalton, 1803)• Thomson - Plumb Pudding Model (1897)• Photoelectric effect (Einstein, 1905)• Solar System (planetary) Model – Rutherford 1908• Bohr (Semi-Classical) Model (1913)• Electron Cloud (Quantum Mechanical) Model (1920s)• Standard model (quarks) – current

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ST03 – Electronics – particle level: structure of matter

Basic atomic properties

• small, massive nucleus surrounded by smaller, lighter electrons• nucleus consists of protons and neutrons

• Binding energy – electrostatic force and centripetal force• Energy quantized - stable shells – energy orbits• Valence shell – material properties

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ST03 – Electronics – particle level: structure of matterHydrogen – single electron system

• Bohr (semi-classical) model

• 1. The orbiting electrons existed in orbits that had discrete quantized energies. That is, not every orbit is possible but only certain specific ones.

• 2. The laws of classical mechanics do not apply when electrons make the jump from one allowed orbit to another.• 3. When an electron makes a jump from one orbit to another the energy difference is carried off (or supplied) by a single

quantum of light (called a photon) which has an energy equal to the energy difference between the two orbitals.• 4. The allowed orbits depend on quantized (discrete) values of orbital angular momentum, L

• Accurate only for single-electron systems

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ST03 – Electronics – particle level: structure of matterHydrogen – single electron system

• QM model• Wave-particle duality – uncertainty principle• No exact position – only a probability that

a particle can be found in a certain point

• As we deal with probabilities, we can make a relationship to long exposition photography (persistence)

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ST03 – Electronics – particle level: structure of matterHydrogen – single electron system

• QM model• Possible relationship between orbit and orbital (not exact)

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ST03 – Electronics – particle level: structure of matterHydrogen – single electron system

• QM model• Electron orbitals

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ST03 – Electronics – particle level: structure of matter

Photoelectric effect – effect of field on the shell

• QM model• Light is seen as particle – although it can be also seen as EM wave

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ST03 – Electronics – particle level: structure of matter

Hydrogen transition

• Transition – effect of change of energy – could be from a photon

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ST03 – Electronics – particle level: structure of matter

Free electron

• Back to the long exposition analogy • Hard to visualize a free electron – after a given time, it could be

theoretically be anywhere - particle in a box

• Can think of it as a localized wave-packet

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ST03 – Electronics – particle level: structure of matter

Free electron

• For many free electrons – correspondence between wave model and particle point model is more obvious

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ST03 – Electronics – particle level: structure of matter

Multi-electron atoms

• Bohr model

• QM model

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ST03 – Electronics – particle level: structure of matter

Bonding – molecules and crystals

• Ionic bonds form between positive and negative ions (atoms). In an ionic solid, the ions arrange themselves into a rigid crystal lattice. NaCl (common salt) is an example of an ionic substance.

• Covalent bonds are formed when atoms share electrons with each other. This gives rise to two structures: molecules and covalent network solids. Methane (CH4) is a covalent molecule and glass is a covalent network solid.

• Metallic bonds occur between metal atoms. In a metallically bonded substance, the atoms' outer electrons are able to freely move around - they are delocalised. Iron is a metallically bonded substance.

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ST03 – Electronics – particle level: structure of matter

Bonding – covalent

• Covalent bonds are formed when atoms share electrons with each other. This gives rise to two structures: molecules and covalent network solids. Methane (CH4) is a covalent molecule and glass is a covalent network solid.

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ST03 – Electronics – particle level: structure of matter

Metallic bonding and conductivity

• Metallic bonds – one valent electron – becomes free easily• Sea of electrons (electron cloud) – binding with positive metal ions

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ST03 – Electronics – particle level: structure of matter

Metallic bonding and conductivity

• Metallic bonds – one valent electron – becomes free easily• Sea of electrons (electron cloud) – binding with positive metal ions

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ST03 – Electronics – particle level: structure of matter

Metallic bonding and conductivity

• Surface states

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ST03 – Electronics – particle level: structure of matter

Metallic bonding and conductivity

• Complex issue – but for us it is enough to work with the Drude model