Cold emission

There will always be a position a, where the electron has positive kinetic energy even though it is outside the metal and there will be a finite probability that it leaks through the barrier and leaves the metal permanently, in a process of cold emission. 

Experimentally, work-function measurements which rely on the cold emission of electrons are carried out in the field-emission microscope (F.E.M.) (21). The apparatus, as shown in Fig. 11, consists of a W tip P sharpened by electrolytic polishing so that the radius of curvature is 10 cm., and an anode in the form of a film of Aquadag. A variable potential of 3 to 15 kv. is applied to the anode, and the electrons, pulled out from the point, travel in approximately straight lines to the fluorescent screen. The linear magnification obtained is of the order of 10 to 10. The secondary electrons from the screen are collected by the anode, and the field-emission current is measured by a sensitive microammeter. 

The field emission microscope utilizes the phenomenon of cold emission as follows A wire etched to a very sharp point is surrounded by a spherical anode, usually in the form of a fluorescent screen. The system is evacuated to pressures of the order of 10 to 10 mm, of Hg and the wire is heat-polished electrically. This outgasses the metal and produces a smoothly... 

The phenomenon of electron emission under the action of a strong external electric field on a metal has been known since the end of the 19th century. By the early 1920s this phenomenon had been comparatively well studied experimentally. The main features of cold emission have been theoretically explained by Fowler and Nordheim [31] on the basis of the ideas of electron tunneling. 

Here, v is the velocity corresponding to the Fermi energy. One can see that cold emission has certain similarities with the ionization of atoms by the external electric field (see Sect. 2.1). 

The exponential factor can be seen to have the same dependence on parameters as in the cases of atom ionization by the electric field and cold emission of electrons from metals. 

Concepts relating to the tunneling of particles through a potential barrier were introduced in pioneering works in physics immediately after the creation of quantum mechanics and were used to account for such phenomena as a-decay of atomic nuclei [1,2], cold emission of electrons from metals [3] and the ionization of atoms in strong electric fields [4],... 

The results on examination of the electric conductivity and cold emission, as well as the mechanical and biological properties of the new carbon material, clearly show it can be employed in a broad field of applications, such as microelectronics, machine-building, etc. The excellent biological properties of Tetracarbon make it the best material for many applications in medicine. 

Practically inexhaustible possibilities are latent in the methods based on the external and internal photoelectric effects excited by x rays and light of various wavelengths. It is worth mentioning specially the methods of electron (p) spectroscopy, cold emission, photoelectric emission, and photoelectron spectroscopy, the last being used widely for the purpose of chemical analysis. 

The cold emission of electrons from a metal cathode at a hlgji negative voltage ( ). 

It is interesting to note that no matter what kind of microwave vacuum device, most electron devices fimction based on the principles of velocity modulation, electron bunching, and electrodynamic induction for microwave generation and ampHfication. The only microwave vacuum devices not based on velocity modulation, electron bunching, and electrodynamic induction are monolithicaUy developed solid-state vacuum diode or triode. These devices are microscopically small and incorporate cathodes. The operating electric fields are strong enough for cold emission from the cathode. 

The field ionization process can be considered as the reverse of a cold emission process. In the former, the electrons were injected... 

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