High-energy electron beam

Materials having a higher vapor pressure at low temperatures ate typically vaporized from resistively heated sources such as those shown in Figure 5a. Refractory materials requite a high temperature to be vaporized. A focused high energy electron-beam heating is necessary for vaporization (Fig. 5b). 

Janke, C.J., Lopata, V.J., Havens, S.J., Dorsey, G.F. and Moulton, R.J., High energy electron beam curing of epoxy resin systems incorporating cationic photoinitiators, US Patent 5,877,229, 1999. 

When a high-energy electron beam in an electron microscope hits a sample, a wealth of information becomes available through a number of scattering, diffraction and decay processes (Fig. 4.13). Indicate how these may be used to obtain additional information about the sample. 

Chemical fixation for transmission electron microscopy prepares cells for the preservation of damage due to subsequent washing with aqueous solvents, dehydration with organic solvents such as ethanol or acetone, embedding in plastic resins, polymerization of the resins by heat, exothermic catalysts, or ultraviolet radiation, and imaging with high-energy electron beams in an electron microscope. 

In a simple electron microscope, a primary beam of electrons is produced using a conventional electron gun, where a heated cathode, maintained at ground potential, emits electrons which are drawn out by a positive potential (typically 30 kV) to form a high energy electron beam. This beam is easily electrostatically and/or magnetically focused (since electrons are charged particles) to a few microns across, and can be directed to any point on the sample by a series of magnetic lenses. The system must be evacuated to reduce attenuation and scatter of the electron beam. When an electron beam strikes the sample, a number of processes take place (Fig. 5.6 Pollard and Heron 1996 51). 

Positive ions are produced by bombarding neutral atoms or molecules in the vapour phase with a high energy electron beam in the ionisation chamber. One (or sometimes two) electron are ejected from the outer most shells. 

The fluorescence process used in some x-ray sources, as described in Section 10.1, can also be used as an analytical tool. One can direct either high-energy electron beams or x-rays at an unknown sample and perform qualitative and quantitative analysis by making measurements on the lower-energy x-ray emissions that occur. Let us first briefly review what we have discussed to this point concerning the concept of fluorescence. 

What is the purpose of the high-energy electron beam utilized in a mass spectrometer ... 

The high-energy electron beam is used to fragment the molecules of the analyte into particles of mass-to-charge ratios characteristic of that molecule. 

The sample surface is bombarded with an incident high energy electron beam, and the action of this beam produces electron changes in the target atoms the net result is the ejection of Auger electrons, which are the characteristics of the element. Because of the small depth and small spot size of analysis, this process is most often used for chemical analysis of microscopic surface features. 

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