Skip to main content
Engineering LibreTexts

2.4.4 Summary to: Conductors - Special Applications

  • Page ID
    2772
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    Thermionic emission provides electron beams. The electron beam current (density) is given by the Richardson equation:

    \[j=A\cdot T^2 \cdot \text{exp}\left(-\frac{E_A}{kT}\right)\]

    • 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 I, i.e. one of the junction may "cool down".
    Used for electrical cooling of (relatively small) devices. Only big effect if electrical heating ( I2) is small.

    2.4.4 Summary to: Conductors - Special Applications is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

    • Was this article helpful?