This essay discusses that the advent of electron microscopy began with the development of electron optics by Hans Busch (Klein, Buhr and Frase 2012, 298). This soon gave way to the invention of the first electron microscope by Ruska (Klein, Buhr and Frase 2012, 298)…
Theoretically, a light microscope’s magnification power is infinite, while its resolving power is limited to 200 nm because of the fixed wavelength of photons in visible light (Carter & Shieh 2009, 135). Due to this limitation, the magnification of extremely minute objects at the microscale and nanoscale by a light microscope is not possible. On the other hand, electron microscopy uses electrons rather than photons. As electrons have very short wavelengths compared to photons, electron microscopes achieve a much higher resolution than what is achievable by a light microscope. In fact, the resolving power of an electron microscope is 1000 times that of a light microscope (Carter & Shieh 2009, 135). Electron microscopy is of two major types – Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM). While both types employ electrons for magnification, they vary in their design and application. Proprieties and Uses of TEM and SEM Transmission Electron Microscope (TEM) The design of TEM is similar to that of a light microscope. Electrons in the electron beam that is focused on the sample are accelerated up to 200 kV before hitting the specimen (Klein, Buhr and Frase 2012, 300). The specimen is of a very thin section. Electromagnetic lenses are used to condense, focus and guide the electron beam onto the specimen. The specimen is treated chemically for increasing the contrast in the magnified image of the specimen (Carter & Shieh 2009, 136). Heavy metals are usually used for staining. Once the electrons hit the specimen, they pass through it and are then collected and projected via electron optics onto a screen (Klein, Buhr and Frase 2012, 300). A magnified image of the object appears on the screen. The image can also be recorded digitally and viewed on a computer when a scintillator converts the hitting electrons into pulses of light that can be detected using a charge-coupled device (Klein, Buhr and Frase 2012, 300). Two-dimensional images are created according to variations in the intensity of electrons hitting the detector (Carter & Shieh 2009, 136). TEM has a large number of applications in innumerable fields ranging from life sciences to material science. TEM has proved to be a priceless tool for studying the ultrastructure of metals (Egerton 2005, 14). In life sciences, it is used for studying bacteria, viruses, and tissues of plants and animals (Egerton 2005, 14). TEM has great applicability in examining the ultrastructure of cell organelles and membranes. Scanning Electron Microscope (SEM) One of the limitations of TEM is that the specimen to be examined has to be made very thin as thicker specimens absorb electrons instead of transmitting them (Egerton 2005, 17). SEM, on the other hand, can be used for bulky specimens. It is used for a detailed study of the surface of the specimen (Carter & Shieh 2009, 136). In a SEM, the electron beam is scanned over the surface of the specimen that is coated with platinum or gold. As the electrons interact with the specimen surface, different types of signals are emitted based on the surface topography. The sample’s surface reflects secondary electrons of low energy and high-energy backscattered electrons are released from below the surface (Carter & Shieh 2009, 137). The signals are collected and the image is processed. A three-dimensional image of the specimen is obtained pixel by pixel. ...
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The above micrographs represent a Secondary electron image (SE) and a Backscatter electron image (BSE) of the same region of an asbestos sample.The SE image appears more three dimensional than the BSE image. The cluster of fibers at the center in the SE image appears more rounded, while the one in the BSE appears flat.
Images in TEM are obtained by focusing an electron beam on the specimen. The electrons are absorbed, transmitted, scattered or backscattered. Depending on the kind of image required by the operator, either the transmitted electrons (called direct beam) or the scattered electrons (called diffracted beam) is selected.
This essay analyzes that spherical aberration also occurs in the Electron Microscopes when electrons passing through the side of the lens are refracted greater than those passing along the axis.2 (Lam, 2009); while Diffractive aberrations are brought about by the deviations from geometrical optics caused by the wave nature of light.
This essay demonstrates that the working principle of a TEM is that when electrons are accelerated up to high energy levels and then focused onto a specimen, they scatter or backscatter elastically or in-elastically, producing many different interactions that are a source of signals like X-Rays, enabling magnification of ultra-microscopic particles.
From this paper it is clear that to obtain such a pattern, the selected area aperture is placed in the image plane of the objective lens and used to select only one part of the image. Using projector lenses to focus on electron beams to obtain small spots on the object surface, the diffraction patterns can be obtained.
Attrition is the wear to teeth caused due to interaction between the teeth itself. Excessive loads can cause micro fractures in the enamel region. This is termed as Abfraction. (Adrian Lussi, 2006) Erosion of teeth on the other hand is a result of its interaction with acidic foods which causes decay to the teeth surface in a variety of ways.
Scanning electron microscopy (SEM), as well as other techniques such as energy dispersive spectroscopy (EDS) is an effective tool used for the identification and characterization of particulate contamination and foreign body contamination of food.
This essay analyzes that in an electron microscope, the electrons are accelerated in a vacuum until their wavelength is shortened. Shorter wavelengths can be produced by increasing the voltage. Beams of these fast-moving electrons are focused on an object. The object either absorbs these beams and forms an image on an electron-sensitive photographic plate.
Besides, attenuation of the primary electron beam will also be lesser. This will lead to better image quality and better microanalytical capability of a TEM. Besides, minimizing molecule – electron beam interaction, better vacuum level
The key feature of this paper is the practice of restricting competition in modern markets. Competition is a very important constituent of a market. It makes the competing firms perform to the best of their ability. At the end, the consumers get a high
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