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Chemical Instrumentation Edited by GALEN W. EWING, Seton Hall University, So. Orange, N. J. 07079
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These articles are intended to serve the readers O ~ T H I JOURNAL S
by calling attention to new developments in the theory, design, w availability of chemical laboratory inslrumentation, or by presenting useful insights and ezplanations of topics that are of practical importance to those who use, w teach the use of, modern instrumentation and instrumenlal techniques. The editor invites correspondence from prospective contributors.
LXVI. Scanning Electron Microscopy-Part
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Annemarie C. Reimschuessel Allied Chemical Corporation, Box 1021 R, Morristown, N . J. 07960 The scanning electron microscope is, as the name implies, a microscope, and as such is used t o magnify details of a particulilr object. I t is a rather recently developed member of the family of electron microscopes and has already been extensively, but not exclusively, used for the study of surfaces of solid materials. I n order to appreciate the unique features of this instrument it is well to recall briefly some characteristics of both the optical microscope and the conventional electron microscope. There exists a. striking similarity between these two instruments with respect t o the. arrangement and the principle functions of their basic components. This is shown schemstically in Figure 1. Each of the considered systems utilizes electromagnetic radiation for interaction with the object to render mieroscopicd detail visible. Whereas electrons serve as "illumination" in the electron microscope, visible light i5 used in the optical or "light" microscope to obtain an image of the object,. Sources of illumination for the optical microscope (OM) range from simple
light bulbs and low voltage lamps to mercury humers and Xenon arc illominators. The beam of light is condensed by a system of glass lenses (condenser) and transmitted t,hrough or reflected by the object. The magnified image is then produced by additional systems consisting of objective and projector lenses. The electron beam used as illumination in the conventional transmission electron microscope is generated in high vacilum by thermionic emission from a tungsten wire hairpin filament. I t is then condensed by electromagnetic lenses, transmitted through the object and the pradnred image focused and projected with the aid of additional eleetrom~gneticlenses onto either a fluorescent screen or photographic plate. The physical phenomena significant for image formation are absorplian and refraction in ease of the lieht microsco~eand scattering may be elastic or inelastic, which means without or with loss of energy. The most widely recognized difference between the optical and electron microscopes is in their respective powers of resolution. The resoh~tion is defined
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Mrs. Annemarie C. Reimschuessel ~dltilli~ed i n G c I ~ I I : nlld ~ ~
