Use of Electron Microscopy for Investigating Teeth Erosion Essay

Use of Electron Microscopy for Investigating Teeth Erosion - Essay Example 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-dimensio nal 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.