The Principles and Types of Electron Microscope - Essay Example

Electron Microscopy Electron Microscopy refers to a type of microscopy that uses a beam of electrons to create an image of a specimen. Electron microscopy has a higher magnification and better resolving power than the light microscopy. In this respect, it is possible to see finer details and smaller objects compared to other forms of microscopy. The basic component of electron microscopy is an electron microscope which is complex equipment that generally stands alone in a specially designed room and is operated by trained personnel. The process of magnification in electron microscopy is based on the carefully placed electromagnetic fields to focus the negatively charged electron particles (Chandler and Robert, 157). The higher magnification is also achieved because the waves of electron particle are approximately four times shorter than light waves (Chandler and Robert, 158). The Principles and Types of Electron Microscope The technology involves the substitution of a series of electric and beam of electrons which form electromagnetic fields instead of light beams and optical glass lenses used in most light microscope. Electron Microscopes apply the principle of electromagnetic and electrostatic lenses to regulate the direction of electrons. The electron beam used in the electron microscopy is much shorter wavelengths thus allow higher degree of resolution as well as high contrast. The principle of magnification by the electron lenses is based on several stages and each stage must take place in a vacuum (Chandler and Robert, 161). The electron beam first goes through a tiny aperture in a positively charged anode then is passed through the condenser which is the first electromagnetic lens. The function of the condenser is to concentrate the beams which are very important for increasing the focus. This is achieved by bending the electron paths towards an axis as is seen in converging glass lens. Since electrons are very sensitive to magnetic fields, they can be controlled by changing the current passing through the lenses (Chandler and Robert, 162). Figure 1: Parts of Electron Microscope Source: Chandler and Robert, 162 After focusing the beams by the condenser lens, the highly concentrated electron beam then strikes in a different chamber that is sealed by a carefully prepared known as O-rings. The specimen prepared is what the beam of light passes through in order to magnify it. The varying levels of material density also play a vital role in the magnification process since the beam is also made of particles. This is what influences the lightness or the darkness of the final image that is viewed by the operator. In this respect, the preparation of the material placed on the specimen itself is very important. According to Chandler and Robert (171), the effect of bombardment will therefore vary according to the thickness of the material under microscopy. When an electron beams passes through the specimen downwards it comes across two other electromagnetic lenses that create electromagnetic fields thus the path of the electron beam is highly influenced. `First the concentrated beams created by the condenser lens are spread then the resultant image is capture by a more sensitive projector lens which is then recorded in a fluorescent as a picture. The image that is capture in this screen is just the same as the images in common photography and would appear lighter when it is highly exposed through higher dense areas but darker when under exposed. The electron waves are approximately four times shorter than those in the light waves thus resulting into higher resolution. This technology resulted into its popularity and advancement in research and commercialization. The images that are derived from electron microscopy are clear and contain finer details of the object under view. Up to this point, the type of microscope is called Transmission Electron Microscopy. The second and more advanced electron microscopy involves the use of Scanning Electron Microscope (SEM). Unlike the transmission electron microscope in which electrons in the primary beam are transmitted through a sample, the scanning electron microscopes images are produced by detecting secondary electrons which are emitted from the surface as a result of excitation from primary electron beam (Chandler and Robert, 181). In scanning Electron Microscope the image is constructed in time sequence using a tinier electron beam than that used in the transmission microscope. In this respect, the specimen is scanned and there is no direct passage of beams through the specimen. The image is gotten from secondary electron currents often originating from a thin layer within the atomic structure of the examined specimen (Chandler and Robert, 179). Even though the images in Scanned Electron Microscope provides an image with full topographical information in a 3D though still in black and white. The Scanned Electron Microscope also uses less accelerating voltages to limit the penetration of beam into sample since it only uses secondary generated electrons from the surface structure of a sample thus the use of low voltage for examination of biological samples. Sample Preparation Sample preparation is a very important procedure in electron microscopy since it determines the quality of image. Another reason for effective sample processing is because the inner part of electron microscope is under high vacuum that is meant to facilitate straight line travelling of beams. However, the technique required is dependent on a number of variables including the type of analysis, specimen as well as the type of microscope. The first process in preparation of samples for electron microscope examination starts from preservation of the samples. Cryofixation is a procedure used to preserve specimen by rapidly freezing the specimen in a snapshot but with very minimal artifacts (Chandler and Robert, 205). This process is often combined with fixation that ensures specimens are preserved in the freshest way as possible. Dehydration is also done in certain cases depending on the type of specimen. Dehydration is a process of removing water from sections of the sample are replaced with organic solvents like acetone and ethanol before final drying. This is mainly used in scanning electron microscope. Embedding is another procedure used for preservation of specimen for examination under electron microscope and it involves transforming specimens into hardened block through the process of polymerization. Sectioning which is the production of thin slices of the specimen for examination is the second stage in sample preparation. Unlike in light microscopy, electron microscopy requires thinner sections of the specimen so that they are translucent and allows beams of electrons to pass through. The recommended thickness is usually 90nm and is prepared using diamond knife or an ultra-microtome. Sectioning however depends on the type of sample and the image to be viewed. Sectioning is followed by staining which involves the use of heavy metals such as uranium and lead to scatter imaging electrons in order to give contrast between different structures because many specimens are nearly transparent to the electron beam (Chandler and Robert, 211). Staining is an important procedure since it adds electron density to the specimen resulting into enhancement of contrast since there will be more interactions between the primary beam electrons and those of the sample (Chandler and Robert, 227). This procedure can come after or before embedding depending on the material being examined under electron microscope. Sputter coating is another procedure used in the final stages of preparation of the sample before examination under an electron microscope. It is a thin coating done using electrically conducting material by low vacuum on the sample in order to prevent charging of the specimen. Charging of the specimen is possible due to the fact that charging of specimen can occur because of the accumulation of the static electric fields caused by electron irradiation during imaging (Chandler and Robert, 228). Sputter coating is also important since it improves the quantity of secondary electrons that can be detected from the sample’s surface of the Scanning Electron Microscope thus improves the signal to noise ratio. The most common materials used in sputter coating include platinum, gold, chromium and palladium. While sample preparation differs depending on the type of material and examination to be done, it is important to ensure samples are properly processed to enhance maximum magnification and finer details. Scientific Application of Electron Microscopy Both Scanning Electron Microscopy and transmission Electron Microscopy are used scientifically and industrially. The mode of application varies depending on the main objective of the scientific research or an experiment. For instance, in dark-field electron microscopy, the angle upon which bombardment of electron beam is tilted in darker field to produce brighter spots mainly to determine whether there exist crystalline structures within the specimen. This is of very importance in the field of crystallography and analysis of minerals. Computerized simulations coupled with the high end ability of Scanning Electron Microscopy have been used in petroleum industry and their byproducts to examine synthetic materials or petrochemicals (Li, 19). Electron Microscopy is also applied in the fields of biology in the examination of cells and microorganisms which is useful in the study of cell structures and morphology. All these uses of electron microscope can either be investigative or applied depending on the field and objective of the organization. Appendix Basic Parts of an Electron Microscope Chandler, Douglas E., and Robert W. Roberson. Bioimaging: Current Concepts In Light And Electron Microscopy. Sudbury, Mass: Jones and Bartlett Publishers, 2009 Works Cited Chandler, Douglas E., and Robert W. Roberson. Bioimaging: Current Concepts In Light And Electron Microscopy. Sudbury, Mass: Jones and Bartlett Publishers, 2009. Li, Jian. "The Industrial Application of Advanced Electron Microscopy." JOM 58.3 (2006): 19. ProQuest. Web. 16 Nov. 2014 Read More