Transmission Electron Microscope - Assignment Example

TRANSMISSION ELECTRON MICROSCOPE Researches, diagnostics, and crime analysis could not be done and completed without studying and analyzing minute particles which cannot be seen by the naked eye. In the early centuries, light microscope has been used but is limited by the wavelength of visible light and therefore cannot penetrate deeply into the specimen which is the object of the study. The existence of microscope specifically transmission electron microscope has made these researches and diagnosis faster and more cures and crime detections are made. Transmission electron microscope (TEM) is an instrument commonly used in science which uses electrons instead of light to visualize small objects at a very fine resolution. The resolution is increased relative to the shortness of the wavelength of the electron beams. Instead of lenses the electrons are focused by electromagnetic fields and form an image on a fluorescent screen, like that of a television screen. It also provides a resolution and a magnification of up to 100,000x greater than light microscope in the nanometer range. The scrutiny of an object using TEM reveals the identification of the following: (1) topography which is the surface features of an object; (2) the specific shape and size of a particle making up an object termed as morphology; (3) composition, the elements and compounds that the object is composed of and its relative amounts; (4) crystallographic information, that is how the atoms are arranged and its relationship as to the material properties. However, one problem with TEM is that, since electrons have poor penetrating power, the sections to be examined must be very thin – less than 50 nm thick. This necessitates the use of special hard embedding media (plastics) and special ultramicrotomes to cut such thin sections. Steel knives cannot be used to cut these sections, either glass or diamond knives are used. According to an article “The World of Forensic Science” retrieved from http://www.enotes.com, “the combination of the resolving power of the electrons, and the image magnification that can be subsequently obtained in the darkroom during the development of the film, produces a total magnification that can be in the millions.” HOW TRANSMISSION ELECTRON MICROSCOPE WORKS Transmission electron microscope works similarly with any light microscope but instead of light electrons are used as a “light source”. The lower wavelength of electrons gives high resolution better than the light microscope. The higher magnification allows the study of minute details in a cell or other materials down to near its atomic level. Hence, it is best used in medical, biological, other materials research. In the article entitled “The Electron Microscope” as cited in http://nobelprize.org magnetic lenses guide the electrons and this is how it goes: “a “light source” at the top of the microscope emits the electrons that travel through vacuum in the column of the microscope. Electrons are focused into a very thin beam by the use of electromagnetic lenses instead of glass lenses and travel to the specimen being studied. The thickness or thinness of the specimen affect the transmission of electrons, thicker specimen would mean that a few electrons are scattered. At the bottom of the microscope the unscattered electrons hit a fluorescent screen, which gives rise to a “shadow image” of the specimen with its different parts displayed in varied darkness according to their density. The composition or nature of the object in study can then be seen by the user.” Technically speaking, Themionic gun is used by majority as a source of electron which produces a stream of monochromatic electrons. The condenser lenses 1 and 2 then focused the stream into small, thin, coherent beam. The first lens is usually controlled by the spot size knob while the second lens is controlled by the intensity or brightness knob. Electron beams are then restricted and unwanted scattered electrons are filtered out before image formation by a thin disk that is Read More