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Scanning Electron Microscope - Essay Example

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Scanning Electron Microscope Instructor: Scanning Electron Microscope The scanning electron microscope utilizes a beam of focused high-energy electrons for the generation of various signals on the surface of specimens (Reimer, 2008 p97)…
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Scanning Electron Microscope
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Download file to see previous pages Areas that range from a width of one centimetre to as minute as five microns can be seen in scanning mode using techniques in scanning electron microscopy. The magnification ranges from 20X to 30,000X with spatial resolution of fifty to one hundred nanometres. The SEM also has the capability of analysing specific locations found on the sample, with this approach being particularly useful in semi-quantitative and qualitative determination of crystal orientations, crystalline structure, and chemical compositions. A scanning electron microscope images samples via scanning them with electron beams with the sample in a raster scan pattern (Reimer, 2008 p 97). The electrons released by the SEM interact with sample atoms and produce signals that consist of information revealing the composition and topography, as well as electrical conductivity. In its functioning, accelerated electrons carry specific amounts of kinetic energy which is dissipated in form of various signals derived from interactions between the sample and the electrons (Reimer, 2008 p97). This occurs when the electrons incident on the sample are decelerated on contact with the sample. The received signals could be in form of secondary electrons, heat, visible light, photons, and diffracted backscattered electrons. Backscattered electrons and secondary electrons are usually utilized for sample imaging, with secondary electrons also used for showing the topography and morphology of the sample with backscattered electrons are used for contrast illustration of multiphase sample composition. X-rays are produced by through inelastic collisions of electrons incident on the sample and the electrons present in the sample atom’s discrete shells. During these electrons return to their lower energies, they give out fixed wavelength X-rays. Each element in the mineral being investigated produces X-rays which are characteristic to it when excited by the beam of electrons. This process is non-destructive as these X-rays do not cause any change in volume of the sample when they are lost. Thus, the same material can be investigated continuously. A scanning electron microscope has the following essential components (Reimer, 2008 p90): Source of electrons Electron lenses Stage for the sample Sensors for detecting all signals required Devices for data output and display Power supply, cooling system, vacuum system, electric and magnetic field free room, and a vibration free floor SEMs will always possess one detector usually for detection of secondary electrons, with most having more detectors. The accommodated detectors critically determine the instrument’s specific capabilities. Scanning electron microscopes are normally used for the generation of high-resolution images of various samples and their chemical spatial variations (Goldstein, 2009 p63). They aid in the acquisition of elemental maps or EDS assisted spot chemical analysis and phase discrimination using the sample atoms’ mean atomic number. They also give the compositional maps which they base on trace element differences. The scanning electron microscope is also used for the identification of phases with basis on crystalline structure and/or qualitative chemical analysis (Goldstein, 2009 p63). Specific measurement of extra small features which could be to fifty nanometres in size can also be done using scanning electron ...Download file to see next pagesRead More
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