The spatial variation in this information (the "image") may be viewed by projecting the magnified electron image onto a fluorescent viewing screen coated with a phosphor or scintillator material such as zinc sulfide. When it emerges from the specimen, the electron beam carries information about the structure of the specimen that is magnified by the objective lens system of the microscope. The electron beam is accelerated by an anode typically at +100 k eV (40 to 400 keV) with respect to the cathode, focused by electrostatic and electromagnetic lenses, and transmitted through the specimen that is in part transparent to electrons and in part scatters them out of the beam. The electron beam is produced by an electron gun, commonly fitted with a tungsten filament cathode as the electron source. The original form of the electron microscope, the transmission electron microscope (TEM), uses a high voltage electron beam to illuminate the specimen and create an image. Operating principle of a transmission electron microscope Types Transmission electron microscope (TEM) Although current transmission electron microscopes are capable of two million-power magnification, as scientific instruments, they remain based upon Ruska's prototype. Siemens produced a transmission electron microscope (TEM) in 1939. The first North American electron microscopes were constructed in the 1930, at the Washington State University by Anderson and Fitzsimmons and the University of Toronto, by Eli Franklin Burton and students Cecil Hall, James Hillier, and Albert Prebus. Siemens produced the first commercial electron microscope in 1938. Also in 1937, Manfred von Ardenne pioneered the scanning electron microscope. Four years later, in 1937, Siemens financed the work of Ernst Ruska and Bodo von Borries, and employed Helmut Ruska, Ernst's brother, to develop applications for the microscope, especially with biological specimens. In the following year, 1933, Ruska built the first electron microscope that exceeded the resolution attainable with an optical (light) microscope. In 1932, Ernst Lubcke of Siemens & Halske built and obtained images from a prototype electron microscope, applying the concepts described in Rudenberg's patent. In May of the same year, Reinhold Rudenberg, the scientific director of Siemens-Schuckertwerke, obtained a patent for an electron microscope. The apparatus was the first practical demonstration of the principles of electron microscopy. The first prototype electron microscope, capable of four-hundred-power magnification, was developed in 1931 by the physicist Ernst Ruska and the electrical engineer Max Knoll at the Berlin Technische Hochschule or Berlin Technical University. In 1926, Hans Busch developed the electromagnetic lens.Īccording to Dennis Gabor, the physicist Leó Szilárd tried in 1928 to convince him to build an electron microscope, for which he had filed a patent. Modern electron microscopes produce electron micrographs using specialized digital cameras and frame grabbers to capture the images.ĭiagram illustrating the phenomena resulting from the interaction of highly energetic electrons with matter Industrially, electron microscopes are often used for quality control and failure analysis. A scanning transmission electron microscope has achieved better than 50 pm resolution in annular dark-field imaging mode and magnifications of up to about 10,000,000× whereas most light microscopes are limited by diffraction to about 200 nm resolution and useful magnifications below 2000×.Įlectron microscopes use shaped magnetic fields to form electron optical lens systems that are analogous to the glass lenses of an optical light microscope.Įlectron microscopes are used to investigate the ultrastructure of a wide range of biological and inorganic specimens including microorganisms, cells, large molecules, biopsy samples, metals, and crystals.
As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a higher resolving power than light microscopes and can reveal the structure of smaller objects. Electron microscope constructed by Ernst Ruska in 1933Īn electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination.
0 kommentar(er)
