2.4.4 Summary to: Conductors - Special Applications

	Thermionic emission provides electron beams. The electron beam current (density) is given by the Richardson equation:			j  =  A · T 2 · exp – EA kT
		Atheo = 120 A · cm–2 · K–2 for free electron gas model Aexp » (20 - 160) A · cm–2 · K–2
		EA = work function » (2 - >6) eV
		Materials of choice: W, LaB6 single crystal
	High field effects (tunneling, barrier lowering) allow large currents at low T from small (nm) size emitter			Needs UHV!
	There are several thermoelectric effects for metal junctions; always encountered in non-equilibrium.
		Seebeck effect: Thermovoltage develops if a metal A-metal B junction is at a temperature different form the "rest", i.e. if there is a temperature gradeient		Essential for measuring (high) temperatures with a "thermoelement" Future use for efficient conversion of heat to electricity ???
		Peltier effect: Electrical current I through a metal - metal (or metal - semiconductor) junction induces a temperature gradient µ I, i.e. one of the junction may "cool down".		Used for electrical cooling of (relatively small) devices. Only big effect if electrical heating (µ I2) is small.
		Questionaire All Multiple Choice questions to 2.4

© H. Föll (Advanced Materials B, part 1 - script)