ST03 – Electronics – particle level: structure of matter 1 Electronics – particle level: structure of matter Lecturer: Smilen Dimitrov Sensors Technology – MED4

ST03 – Electronics – particle level: structure of matter 2 Introduction The model that we introduced for ST

ST03 – Electronics – particle level: structure of matter 3 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

ST03 – Electronics – particle level: structure of matter 4 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

ST03 – Electronics – particle level: structure of matter 5 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

ST03 – Electronics – particle level: structure of matter 6 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

ST03 – Electronics – particle level: structure of matter 7 Hydrogen – 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

ST03 – Electronics – particle level: structure of matter 8 Hydrogen – 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)

ST03 – Electronics – particle level: structure of matter 9 Hydrogen – single electron system QM model Possible relationship between orbit and orbital (not exact)

ST03 – Electronics – particle level: structure of matter 10 Hydrogen – single electron system QM model Electron orbitals

ST03 – Electronics – particle level: structure of matter 11 Photoelectric effect – effect of field on the shell QM model Light is seen as particle – although it can be also seen as EM wave

ST03 – Electronics – particle level: structure of matter 12 Hydrogen transition Transition – effect of change of energy – could be from a photon

ST03 – Electronics – particle level: structure of matter 13 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

ST03 – Electronics – particle level: structure of matter 14 Free electron For many free electrons – correspondence between wave model and particle point model is more obvious

ST03 – Electronics – particle level: structure of matter 15 Multi-electron atoms Bohr model QM model

ST03 – Electronics – particle level: structure of matter 16 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.

ST03 – Electronics – particle level: structure of matter 17 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.

ST03 – Electronics – particle level: structure of matter 18 Metallic bonding and conductivity Metallic bonds – one valent electron – becomes free easily Sea of electrons (electron cloud) – binding with positive metal ions

ST03 – Electronics – particle level: structure of matter 19 Metallic bonding and conductivity Metallic bonds – one valent electron – becomes free easily Sea of electrons (electron cloud) – binding with positive metal ions

ST03 – Electronics – particle level: structure of matter 20 Metallic bonding and conductivity Surface states

ST03 – Electronics – particle level: structure of matter 21 Metallic bonding and conductivity Complex issue – but for us it is enough to work with the Drude model