Materials Properties Electrical properties Magnetic properties Optical properties.
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Transcript of Materials Properties Electrical properties Magnetic properties Optical properties.
Materials PropertiesMaterials Properties
• Electrical properties
• Magnetic properties
• Optical properties
Electrical propertiesElectrical properties
• Ohm’s law• Resistance, resistivity, conductivity
• Matthiessen’s rule
1
l
RA
IRV
ndeformatioimpuritythermaltotal
Electrical resistivityElectrical resistivity
Energy bandsEnergy bands
K L M
discrete energy levels(Pauli exclusion principle)
splitting into energy bands (N=12)
Electron Band StructuresElectron Band Structures
em p ty
filled
metal (e.g. Cu)
energy
valenceband
bandgap
conductionband
filled
em p ty
metal (e.g. Mg)
EF
EF
filled
em p ty
isolators (Egap>2eV)semiconductors
Egap
ConductorsConductors
EF
Semiconductors (intrinsic)Semiconductors (intrinsic)
band gap
n-type Extrinsic Semiconductorn-type Extrinsic Semiconductor
p-type Extrinsic Semiconductorp-type Extrinsic Semiconductor
The p-n DiodeThe p-n Diode
reverse biasforward bias
Magnetic propertiesMagnetic properties
• Magnetic field strength, magnetic flux density, magnetization, permeability, and magnetic susceptibility
1HMMHB
HB
rmm00
0r
The Magnetic FieldThe Magnetic Field
vacuum atmosphere/material
The Magnetic MomentThe Magnetic Moment
orbital contribution=> mlµB
spin contribution=> +/-µB
Bohr magneton: µB=9.27 x 10-24 Am²
Diamagnetic MaterialsDiamagnetic Materials
Paramagnetic MaterialsParamagnetic Materials
Ferromagnetic MaterialsFerromagnetic Materials
The B-H HysteresisThe B-H Hysteresis
remanent flux density
coercive force
Hard and Soft Magnetic MaterialsHard and Soft Magnetic Materials
soft:alternating magnetic fields
hard:permanent magnets
energy productcoercivity
Magnetic StorageMagnetic Storage
coil:magnetic field in gap
magnetic field:induces electriccurrent
Optical propertiesOptical properties
• Transmission
• Refraction
• Absorption
Electro magnetic wavesElectro magnetic waves
electric field E
magnetic field H (perpendicular to E)
light = electromagnetic wavelight = electromagnetic wave
wave: c=(const. light velocity in vacuum=km/s)photons: E=h(Planck constant, 6.63 x 10-34 J/s)
Light Interaction with SolidLight Interaction with Solid
I0=Itransmitted+Iabsorbed+Ireflected
transparenttranslucentopaque
heat
reflection (metals): absorption (electrons excitation by E) => re-emission of photonscolor (e.g. Au, Cu => only partial re-emission)
refraction: transmission into transparent material => decrease in v (n=c/v), bending at interface
AbsorptionAbsorption
Ireflected
Io
x (transparent medium)
Itransmitted
Iabsorbed
Itransmitted=I0(1-R)2exp(-x)absorption coefficientreflectivity
Photon Absorption in a (Semiconducting) SolidPhoton Absorption in a (Semiconducting) Solid1. hole/electron pair generation
Egap,max=hc/min (>3.1eV no visible light absorption=transparent)
Egap,min (max,visible=700nm) (<1.8eV all visible light absorbed=opaque)
2. hole/electron pair generation
in between colored!!e.g. red ruby Al2O3 with Cr2O3 impurity level in the band gap
Light Transmission in AlLight Transmission in Al22OO33
single crystal: transparent
poly-crystal: translucent
with 5% pores: opaque
internal reflection/refraction at grain/phase boundaries – porespolymers: scattering at boundaries betw. crystalline/amorphous regions
Effects/ApplicationsEffects/Applications
luminescenceabsorbing energy => re-emitting visible light (1.8eV<hv<3.1eV)
fluorescence (<1s)phosphorescence (>1s)
e.g. TV (fluoresc. coating) LED (forward bias diode – recombination=> light)
photoconductivityillumination => generation of charge carrierse.g. light meters, solar cells
optical fibres1/0 impulses – high information density 24000 telephone calls by two wires
e.g. 30000kg Cu corresp. to 0.1kg high-purified SiO2 glass
Laser ConceptsLaser Concepts
1. Xe flash lamp excite electrons from Cr3+ ions2. large number of electrons falls back to intermediate state 3. after approx. 3ms: spontaneous emission – triggers avalanche of emissions4. photons parallel to the rod are transmitted to the semi-silvered end
(light amplification by stimulated emission of radiation)(light amplification by stimulated emission of radiation)
monochromatic, high-intensitycoherent red beam