Thermionic emission, charging

The results of several studies were interpreted by the Poole-Erenkel mechanism of field-assisted release of electrons from traps in the bulk of the oxide. In other studies, the Schottky mechanism of electron flow controlled by a thermionic emission over a field-lowered barrier at the counter electrode oxide interface was used to explain the conduction process. Some results suggested a space charge-limited conduction mechanism operates. The general lack of agreement between the results of various studies has been summari2ed (57). 

For typical polymer LED device parameters, currenl is space charge limited if the energy barrier to injection is less than about 0.3-0.4 eV and contact limited if it is laiger than that. Injection currents have a component due to thermionic emission and a component due to tunneling. Both thermionic emission and tunneling... 

The analytic theory outlined above provides valuable insight into the factors that determine the efficiency of OI.EDs. However, there is no completely analytical solution that includes diffusive transport of carriers, field-dependent mobilities, and specific injection mechanisms. Therefore, numerical simulations have been undertaken in order to provide quantitative solutions to the general case of the bipolar current problem for typical parameters of OLED materials [144—1481. Emphasis was given to the influence of charge injection and transport on OLED performance. 1. Campbell et at. [I47 found that, for Richardson-Dushman thermionic emission from a barrier height lower than 0.4 eV, the contact is able to supply... 

For p-type electrodes with doping densities below 1018 cm-3 diffusion and thermionic emission of charge carriers across the SCR is dominant. For p-type doping densities below 1016 cm4 this charge transfer is associated with the formation of macropores, as discussed in Chapter 9. 

Covers charging due to relative motion or separation of two contacting phases in the absence of external electrostatic fields, radiation, or thermionic emission. The superimposition of such effects may serve to confuse the data in many cases, especially those involving natural phenomena. 

Millikan s experiment did not prove, of course, that (he charge on the cathode ray. beta ray, photoelectric, or Zeeman particle was e. But if we call all such particles electrons, and assume that they have e/m = 1.76 x Hi" coulombs/kg. and e = 1.60 x 10" coulomb (and hence m =9.1 x 10 " kg), we find that they fit very well into Bohr s theory of the hydrogen atom and successive, more comprehensive atomic theories, into Richardson s equations for thermionic emission, into Fermi s theory of beta decay, and so on. In other words, a whole web of modem theory and experiment defines the electron. The best current value of e = (1.60206 0.00003) x 10 g coulomb. 

The recombination current density, Jr, can be treated effectively as a Schottky barrier diode current density. Including both thermionic emission and diffusion charge transport mechanisms (13) Jr can be written as... 

One of the important characteristics of gas-solid multiphase flows is concerned with the electrostatic effect. Particles can be charged by surface contact in a collision, by corona charging and scattering in an ionized gas, by thermionic emission in a high-temperature environment, and by other charging mechanisms such as colloidal propulsion... 

The phenomena of the electrification of solids are complex. In gas-solid flows, surface contact by collisions, ion collection, and thermionic emission are known to be the major modes of particle electrification. Details of these three charging modes are introduced in the discussion that follows. 

When solid particles are exposed to a high-temperature environment, typically for T > 1,000 K, charging by thermal electrification becomes important. The electrons inside the solid can acquire the energy from the high-temperature field and be freed by overcoming the energy barrier or the work function. By losing electrons in such a thermionic emission process, the particles are thermally electrified. 

It is noted that the rate of electrification is not constant. Once the tendency is established for an electron to escape from the solid particle by thermionic emission, the charge buildup occurs on the particle, which then attempts to recapture the to-be-freed electron by the attracting Coulomb force. Therefore, the equilibrium of thermal electrification of solid particles in a finite space is possible. Details on the equilibrium and the rate of electrification concerning the thermionic emission are available in Soo (1990). 

The kinetics from here remain even more uncertain, but the polyacetylenes clearly must acquire charge very early in the sequence since charge affects the soot formation from its inception. Other charging mechanisms are present almost certainly once soot nuclei are formed. The experimental ion traces must be evaluated cautiously because of the nonideal wave effects responsible for a pressure and temperature rise during the most rapid soot formation, i.e., the latter part of the fuel-lean combustion. The substantial increase in ionization approximately 1.5 msec after the shock passage cannot be explained by nonideal effects and kinetic arguments. Instead, once the soot is formed, thermionic emission... 

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