Thermionic emission, current

This decrease of work function W is relatively small at reasonable values of electric field E. The Schottky effect can result, however, in essential change of the thermionic current because of its strong exponential dependence on the work function in accordance with the Sommerfeld formula (2-100). Dependence of the Schottky W decrease and thermionic emission current density on electric field are illustrated in Table 2-12 together with corresponding data on field and thermionic field emission (Raizer, 1997). The 4x change of electric field results in 800 x increase of the thermionic current density. 

When a photomultiplier is operated in complete darkness, electrons are still emitted from the cathode. This dark current is mainly due to thermionic emission and is only partly caused by cosmic rays or by radioactive decay of spurious radioactive isotopes in the multiplier material. According to Richardson s law, the thermionic emission current... 

The thermionic-emission current /th> in amperes, generated by a heated filament is described by the Richardson-Dushman equation... 

The proportionality constant fco depends on the physical dimensions of the plate and cathode, their respective geometries, and the ratio of electronic charge to mass. It is sometimes called the permeance. It must be noted that the plate current cannot exceed the thermionic emission current, which provides an upper limit to the value of Ip in Eq. (5.2). A typical characteristic curve is presented in Fig. 5.5, in which... 

Surface-ionization mass spectrometry (SI-MS) studies of organic compounds show that in most cases the compounds decompose into radicals, which have a lower ionization energy IE) than the corresponding molecules, and are ionized more efficiently. For a given type of secondary species, s, formed on the surface, the resulting positive thermionic emission currents (/) and their dependence on surface temperature (7) are described by the ionization efficiency, Ps(7), and by YXT), the yield of chemical reactions on the surface, such that... 

Equation 8.5 is a representation of the carrier flux from the semiconductor to the metal, with the barrier being voltage (V) dependent, ( )b — 12 If from the metal to the semiconductor, with the barrier fixed at ( )b, there exists a parasitic resistance in the circuit such as semiconductor resistance (Rg), the thermionic-emission current expression is modified as... 

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