Electron magnification factor

The identification of size, shape, and axial ratio can also be done by direct observation in the electron microscope (EM). This is accomplished by depositing single molecules (if they can be obtained) directly on polymer-coated copper grids and then shadowing them with heavy metals or making a replica of the molecular surface on mica. The sample can then be viewed in the transmission EM and photographs can then be taken after calibration of the magnification factor. 

The resolution of the microscope was dramatically improved in 1931 by Ruska82 and Knoll83 by using an electron beam instead of visible light, with 40- to 400-keV electrons this is the electron microscope, which by now provides magnification factors as large as 106. There are several varieties ... 

Magnification factors of 10 to 200 000 (routinely 10 to 100000) arc available in a scanning electron microscope. 

Figure 3.49. Slice of a PEM cell showing gas diffusion layer (A), catalyst layer (B) and membrane layer (C), at a magnification factor of 200 (a). Tunnelling electron microscope pictures of catalyst layer at a magnification factor of 500 (b), 18 400 (c) and in (d) 485 500. (From N. Siegel, M. EUis, D. Nelson, M.v.Spakovsky (2003). Single domain PEMFC model based on agglomerate catalyst geometry. J. Power Sources 115, 81-89. Used with permission from Elsevier.)...

In Fig. 3 the apparatus is shown with which Stolte (1972) has performed measurements of this type NO molecules were selected with the help of electrostatic sixpole fields, in accordance with their linear Stark effect in strong fields. The source slit of 0 05 mm width has an image formed by the selected NO molecules in the plane of the detector slit which has an experimental width of 1-4 mm f.w.h.m. this width includes all disturbing effects like the magnification factor (about 18), the imperfect linear Stark effect of the NO molecules in the selected state, the finite width of the transmission of the velocity selector (Av/v = 7% f.w.h.m.) in combination with the chromatic lens errors and the directional dependence of the maximum transmitted velocity of the velocity selector. The j = nij = Q = 3/2 state was selected where 1 is the projection of the electronic angular momentum on the molecular axis. The hyperfine structure of NO influences the situation only slightly. 

Field ion microscopy, or FIM, is a classical technique for the study of surface structure that can yield a structural image with a magnification factor on the order of 10. About 10,000 V are applied between the sample, shaped into a pointed tip (positive pole), and a fluorescent screen in a low-pressure atmosphere of helium. The helium atoms that approach the sample tip loose an electron due to the strong eleelrie field and the resulting He ions are accelerated towards the fluorescent sereen where they form an image. The ionization probability depends on the local intensity of the electric field at the sample, and therefore on the atomic structure. The method is limited to refractory metals such as tungsten, tantalum or iridium. 

Fig. 8. Scanning electron micrographs at low and high magnification (left and right respectively) of fracture surfaces of POM G30 at two extremes of the orientation factor range a) au 0 b) an l. Test conditions 23°C, lOmm/min.

Take electron micrographs at a primary magnification of 50,000-60,000 and further enlarged them by a factor of 2. 

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