![]() The specimen stage holds the specimen perpendicular to the optic axis. In TEM, numbers of condenser lenses are much higher as compared to SEM. In order to realize good contrast and wide range of magnification for viewing very small to larger objects within the specimen, most of the electrons that pass through the specimen should fall within a particular diameter like the screen. The electron gun is followed by a condenser-lens system that converge the illumination and produces an almost parallel electron beam which is incident on the specimen in form of a spot. Most of the accelerated electrons are absorbed by the anode plate and only 1% pass through the fine hole, therefore the beam current in a TEM is typically 1% of the emission current from the cathode. Immediately after emission from the cathode, electrons are accelerated to their final kinetic energy by applying an electric field parallel to the optic axis. The filament is connected to a high voltage supply (about 200-300 kV) which heats it up to about 2700 K, the temperature sufficient for thermionic emission of electrons from tungsten. Electron source, inside the gun is a pointed hair-pin shaped tungsten filament or a spike shaped lanthanum hexaboride source housed in an electron-accelerating chamber. high enough to transverse through the skinny areas of the specimen. The illumination system consists of an electron source, a thermionic gun which emits monochromatic beam of electrons. The components of Transmission electron microscope imaging system are listed as follows ![]() The interaction of the electrons transmitted through the sample forms an image which is 2D, black and white and enlarged and focused on an imaging device, such as a fluorescent screen or on a layer of photographic film or detected by a sensor such as a CCD camera. The beam having accelerated electrons with higher energy levels (a few hundred keV) are focused on a sample or specimen then the electrons are dispersed or back dispersar elastically or inelastic or produce many interactions, providing different signals sources such as X-rays, Auger electrons or light and some of these are used in transmission electron microscope. In Transmission electron microscope, a beam passes through an ultra thin sample that interacts with sample surface because it passes. PRINCIPLE OF TRANSMISSION ELECTRON MICROSCOPE It magnifies upto 50 to 50 million times. This type of electron microscope is invented by Max knoll and Ernst rusker in 1931 at the University of Berlin. TEM is also used for evaluation of nano structures like fibres, particles or micro structure of cell. Transmission electron microscope is a technique of choice for analysis of internal micro structure.
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