There are many kinds of microscopes suitable for general studies; optical microscopes(OM), conventional transmission electron microscopes(TEM), and scanning electron microscopes(SEM). The optical microscopes and the conventional transmission electron microscopes are very familiar. The images of these microscopes are directly formed on an image plane with one or more image forming lenses.
On the other hand, the image of the scanning electron microscope is formed on a fluorescent screen of a cathode ray tube using a scanning system similar to television technique.
In this paper, the features and some applications of the scanning electron microscope will be, discussed briefly.
The recently available scanning electron microscope, combining a resolution of about 200A with great depth of field, is favorable when compared to the replica technique. It avoids the problem of specimen damage and the introduction of artifacts. In addition, it permits the examination of many samples that can not be replicated, and provides. a broader range of information. The scanning electron microscope has found application in diverse fields of study including biology, chemistry, materials science, semiconductor technology, and many others.
In scanning electron microscopy, the secondary electron method, the backscattered electron method, and the electromotive force method are most widely used, and the transmitted electron method will become more useful. Change-over of magnification can be easily done by controlling the :scanning width of the electron probe. It is. possible to continuously vary, the magnification over the range from. 100 times to 100, 000 times without readjustment of focusing.
Conclusion With the development of a scanning electron microscope it is now possible to observe almost all information produced through interactions between substances and electrons in the form of image. When the probe is properly focused on the specimen, changing magnification of specimen orientation does not require any change in focus. This is quite different from the conventional transmission electron microscope. It is worthwhile to note that the typical currents probe, of 10-10 to10-12 A are for below the 10 to 10 A of a conventional Iran Mission microscope. This reduces specimen contamination and specimen damage due to heating. Outstanding features 6f the scanning electron microscope include the stereoseopicobservation of a bulky or fiber specimen in high resolution and observation of potential distribution and electromotive force in semiconductor devices.
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