Electron emission cathodes

Cathodoluminescence (CL), i.e., the emission of light as the result of electron-beam bombardment, was first reported in the middle of the nineteenth century in experiments in evacuated glass tubes. The tubes were found to emit light when an electron beam (cathode ray) struck the glass, and subsequendy this phenomenon led to the discovery of the electron. Currendy, cathodoluminescence is widely used in cathode-ray tube-based (CRT) instruments (e.g., oscilloscopes, television and computer terminals) and in electron microscope fluorescent screens. With the developments of electron microscopy techniques (see the articles on SEM, STEM and TEM) in the last several decades, CL microscopy and spectroscopy have emerged as powerfirl tools for the microcharacterization of the electronic propenies of luminescent materials, attaining spatial resolutions on the order of 1 pm and less. Major applications of CL analysis techniques include ... 

The tube-current stabilizer is usually put in the grounded return output circuit of the high-voltage transformer. The stabilizer functions by properly adjusting the a-c heating current through the filament (x-ray tube cathode), and in this way regulating the electron emission. 

Field emission displays are VFDs that use field emission cathodes as the electron source. The cathodes can be molybdenum microtips,33-35 carbon films,36,37 carbon nanotubes,38" 16 diamond tips,47 or other nanoscale-emitting materials.48 Niobium silicide applied as a protective layer on silicon tip field emission arrays has been claimed to improve the emission efficiency and stability.49 ZnO Zn is used in monochrome field emission device (FED) displays but its disadvantage is that it saturates at over 200 V.29... 

For UV and visible radiation, the simplest detector is a photomultiplier tube. The cathode of the tube is coated with a photosensitive material (such as Cs3Sb, K CsSb, or Na2KSb, etc.) which ejects a photoelectron when struck by a photon. This photoelectron is then accelerated towards a series of anodes of successively greater positive potential (called dynodes). At each dynode, the electron impact causes secondary electron emission, which amplifies the original photoelectron by a factor of 106 or 107. The result is a pulse of electricity of duration around 5 ns, giving a current of around 1 mA. This small current is fed into the external electronics and further amplified by an operational amplifier, which produces an output voltage pulse whose height is proportional to the photomultiplier current. 

Therefore, it must be supposed that the continuous electron emission from the surface of insulating film on the cathode will be existed by the ion bombardment. The work function for the electron emission from the surface of insulating film may be larger than that from the metal surface. Thus the cathode fall in front of the insulating film must be larger than that of metal surface. At a high discharge frequency where the inertia of an... 

In the polymerization process, the charge exchange may be supposed to occur on the substrate. The electron emission from a cathode by ion bomberdment was supposed to exist from the discussion of the discharge phenomena in region I and II. For the extraction of electron from the bound electrons in the atom, relatively large energy may be necessary compared to that from the... 

In many electronic applications, e.g. vacuum tubes, an electron emitting cathode is an indispensable part of the device. For many such devices cold electron emission is favorable because of its lower energy consumption. 

Figure 9 shows an arrangement for measuring secondary electron emission. An electron gun with an incandescent tungsten cathode and the electrodes Bi and Bi is situated in the lower part of the cell. The secondary emitting target P carries the catalyst. A layer of the latter can also be evaporated from Ey or Ei, and deposited on P, which can be heated by radiation or electron bombardment from D. The leads FF of a... 

The potential curves of the adsorption of cesium on a CaF2 surface are given in Fig. 21, which shows that the curve for the ion represents an endothermic chemisorption. By the absorption of light of suitable wave length the system is transferred from minimum B to a point P of the upper curve and an electron is freed and may be drawn off as a photoelectron. The phenomenon of the selective photoelectric effect could be fully explained by this photoionization process (174). By thermal excitation the transfer can be effected at point electron emission of oxide cathodes. Point S is reached by taking up an amount of energy, which may be called the work function of the oxide cathode in this case but which is completely comparable with the energy of activation in chemisorption discussed in Sec. V,9 and subsequently. We shall not discuss these phenomena in this article but refer to a book of the author where these subjects are dealt with in detail (174) ... 

The principal method of introducing metal impurities into early pinch discharges was considered to be arcing. The externally applied voltages, although low, still permit the occurrence of unipolar arcing between the plasma and the wall when driven by the sheath potential. Local electron emission from a cathode spot is balanced by a uniform flow back to the surface of energetic electrons in the tail of the Maxwellian distribution. 

In very pure nonpolar dielectric liquids, electron injection currents at very sharp tips follow the Fowler-Nordheim voltage dependence (Halpem and Gomer, 1969), just as is the case in solid insulators, and in a gas, as described before. In a study of the electrochemical behavior of CNT cathodes (Krivenko et al., 2007) direct experimental proof was found of electron emission into the liquid hexamethylphosphortriamide, which was chosen because it is a convenient solvent for the visualization of solvated electrons at room temperature the solution will show an intense blue coloration upon the presence of solvated electrons. Electron spin resonance showed prove of a free electron. Electrogenerated (as opposed to photogenerated) solvated electrons have been used in the synthesis of L-histidinol (Beltra et al., 2005), albeit that in that work the electrons were generated electrochemically from a solution of LiCl in EtNH2, which is a solvent that is easier to handle than liquid ammonia (boiling points at atmospheric pressure are 17 °C and -33.34 °C, respectively). 

The plasma ionic liquid interface is interesting from both the fundamental and the practical point of view. From the more fundamental point of view, this interface allows direct reactions between free electrons from the gas phase without side reactions - once inert gases are used for the plasma generation. From the practical point of view, ionic liquids are vacuum-stable electrolytes that can favorably be used as solvents for compounds to be reduced or oxidised by plasmas. Plasma cathodic reduction may be used as a novel method for the generation of metal or semiconductor particles, if degradation reactions of the ionic liquid can be suppressed sufficiently. Plasma anodic oxidation with ionic liquids has yet to be explored. In this case the ionic liquid is cathodically polarized causing an enhanced plasma ion bombardment, that leads to secondary electron emission and fast decomposition of the ionic liquid. 

Abstract. This work is devoted to development of the effective electron gun for the triode light sources. The electron gun is based on field emission cathode made of a bundle of PAN carbon fibers encapsulated into a glass capillary. The complex of researches on optimization of electron-optical system has been carried out. 

An efficiency of the cathodoluminescent light source depends directly from the efficiencies of its basic components an electron gun and luminescent covering. The diminishing of the power consumption and the increasing of the cathodoluminescent lamps efficiency are provided with application of field emission cathodes made of carbon fibers. 

The purpose of the current work is the development of the effective electron-optical system for the cathodoluminescent light source with the field emission cathode based on polyacrylonitrile (PAN) carbon fibers [1]. 

The electron-optical system of the cathodoluminescent lamp consists of electron gun and luminescent screen, which is covered by phosphor. It represents the triode construction. The base of this triode is the cathode-modulator unit (CMU) that consists of field emission cathode and extraction electrode (modulator). 

The effective electron-optical system with the field emission cathode based on PAN carbon fibers is developed. Modernization of electron gun design has allowed to decrease operating voltages of the light source essentially and to enhance the cathode current transmitting. 

Abstract. The degradation mechanism of field emission cathodes based on carbon nanostructural materials was investigated in the presented work. Emission current instability came from the adsorption desorption processes on the cathode surface. During the long-time tests the periodical variation of the electron work function (caused by switching on and off of the cathode) was detected. The numerical model was proposed to explain the experimentally observed variations of electron work function. 

Using published results [9], which describe the adsorption process of the active metal on the field emission cathodes surface, one can expect that only first several layers of the adsorbed atoms result in the significant changing of the electron work function in accordance with empirical formula... 

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