Emission secondary electron

The energy for the electron to escape the solid can come from both the potential and kinetic energy of the projectile. If the projectile is an ion, then its energy of ionization is available to deliver energy to the target electrons. The simplest mechanism is that one electron transfers from the conduction band to the ground state of the projectile and another electron acquires this energy difference to escape 

The second process is due to the kinetic energy of the projectile, in which the moving particle interacts with electrons of the solid and transfers sufficient energy to the electron to allow it to escape the solid. This form of electron emission is 

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Edx is based on the emission of x-rays with energies characteristic of the atom from which they originate in Heu of secondary electron emission. Thus, this technique can be used to provide elemental information about the sample. In the sem, this process is stimulated by the incident primary beam of electrons. As will be discussed below, this process is also the basis of essentially the same technique but performed in an electron spectrometer. When carried out this way, the technique is known as electron microprobe analysis (ema). 

Most of the publications dedicated to the interaction between the RGMAs and a solid surface refer to the rare gas - metal system. The secondary electron emission that occurs in the system allows one to judge of the mechanism that deactivates metastable atoms on a metal surface, as well as to evaluate the concentration of metastable atoms in the gaseous phase. 

Fig. 5.20. relationship between the starting velocity v of changes in electrical conductivity of ZnO films with different surface concentration of gold and the current of secondary electron emission J from Mg surface under the action of He [160]. The Au concentration grows in series 2 > 1... 

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. 

Figure 12.20 shows the structure of the side-window circular cage type and linear focused head-on type of photomultiplier which are both preeminent in fluorescence studies. The lower cost of side-window tubes tends to favor their use for steady-state studies, whereas the ultimate performance for lifetime studies is probably at present provided by linear focused devices. In both types internal current amplification is achieved by virtue of secondary electron emission from discrete dynode stages, usually constructed of copper-beryllium (CuBe) alloy, though gallium-phosphide (GaP) first dynodes have been used to obtain higher gains. 

Once electrons have been emitted by the photocathode, they are accelerated by an applied voltage induced between the photocathode and the first dynode (Uq in Figure 3.17). The dynodes are made of CsSb, which has a high coefficient for secondary electron emission. Thus, when an electron emitted by the photocathode reaches the first dynode, several electrons are emitted from it. The amplification factor is given by the coefficient of secondary emission, S. This coefficient is defined as the number of electrons emitted by the dynode per incident electron. Consequently, after passing the first dynode, the number of electrons is multiplied by a factor of 5 with respect to the number of electrons emitted by the photocathode. The electrons emitted by this first dynode are then accelerated to a second dynode, where a new multiplication process takes place, and so on. The gain of the photomultiplier, G, will depend on the number of dynodes, n, and on the secondary emission coefficient, 5, so that... 

Geno, P.W. Macfarlane, R.D. Secondary Electron Emission Induced by Impact of Low-Velocity Molecular Ions on a MCP. Int. J. Mass Spectrom. Ion Proc. 1989, 92, 195-210. 

Modinos, A. (1984). Field, Thermionic, and Secondary Electron Emission Spectroscopy. Plenum, New York. 

The most comprehensive model of secondary electron emission by bare charged particles has been developed by Rudd [62] for secondary electron production by protons ... 

The Influence of Ion-Induced Secondary-Electron Emission on Plasmas... 

In summary, the importance of ion-induced secondary-electron emission in plasma environments is demonstrated by, among other things, the fact that it produces a substantial fraction of the ions, generates significant heating of surrounding surfaces, and modifies the properties of deposited films. 

The interaction of an electron with a surface produces at least three phenomena which are important in a plasma environment. They are (1) chemical reactions between gas phase species and a surface where electron bombardment is required to activate the process, (2) electron-induced secondary-electron emission, and (3) electron-induced dissociation of sorbed molecules. A fourth phenomenon — lattice damage produced by energetic electrons — depends sensitively upon the properties of the material being bombarded, and, it is important in specialized situations, but it will not be discussed in this paper. 

The treatment of secondary-electron emission presented in this section essentially follows the ideas and organization of Sickafus which in turn was strongly influenced by Wolff . Upon entering a solid, an energetic electron is subjected to a sequence of elastic and inelastic scattering events. The collisions produce a cascade of moving electrons. The intersection of the cascade with the surface results in the emission of electrons into the gas phase. Therefore, the externally-observed, energy-... 

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... 

PHOTOEMISSION AND PHOTOMULTIPLIERS. Photoemission is the ejection of electrons from a substance as a result of radiation filling on it Photomultipliers make use of the phenomena of photoemission and secondary-electron emission in order to detect very low light levels The electrons released from the photocathode by incident light are accelerated and focused onto a secondary-emission surface (called a dynode). Several electrons are emitted from the dynode for each incident primary electron. These secondary electrons are then directed onto a second dynode where more electrons are released. The whole process is repealed a number of times depending upon the number of dynodes used, In this manner, it is possible to amplify the initial photocurrent by a factor of 10s or more in practical photomultipliers. Thus, the photomultiplier is a very sensitive detector of light. 

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