FEI_SEM2006_06_AllYouWanted_pb

FEI_SEM2006_06_AllYouWanted_pb - All you wanted to know...

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...but didn’t dare to ask! All you wanted to know about Electron Microscopy. ..
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Introduction This booklet is written for those who know little or nothing about electron microscopy and would like to know how an electron microscope works, why it is used and what useful results it can produce. "With a microscope you see the surface of things. It magnifies them but does not show you reality. It makes things seem higher and wider. But do not suppose you are seeing things in themselves." Feng-shen Yin-Te (1771 – 1810) In The Microscope 1798 A publication of FEI Electron Optics FEI Electron Optics, a division of FEI Company, is one of the world’s lead- ing suppliers of transmission and scanning electron microscopes. Our commitment to electron microscopy dates back to the mid- 1930s, when we collaborated in EM research programmes with universi- ties in the UK and the Netherlands. In 1949, the company introduced its first EM production unit, the EM100 transmission electron microscope. Innovations in the technology and the integration of electron optics, fine mechanics, microelectronics, computer sciences and vacuum engineering have kept FEI at the forefront of electron microscopy ever since. ISBN nummer 90-9007755-3 What is Electron Microscopy? The Transmission Electron Microscope The Scanning Electron Microscope Additional Techniques contents
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4 Nobody knows for certain who invented the microscope. The light microscope probably developed from the Galilean telescope during the 17th century. One of the earliest instruments for seeing very small objects was made by the Dutchman Antony van Leeuwenhoek (1632- 1723) and consisted of a powerful convex lens and an adjustable holder for the object being studied (speci- men). With this remarkably simple microscope (Fig. 1), Van Leeuwenhoek may well have been able to magnify objects up to 400x and with it he discovered protozoa, spermatozoa and bacteria and was able to classify red blood cells by shape. The limiting factor in Van Leeuwenhoek’s microscope was the quality of the convex lens. The prob- lem can be solved by the addition of another lens to magnify the image produced by the first lens. This com- pound microscope – consisting of an objective lens and an eyepiece together with a means of focusing, a mirror or a source of light and a specimen table for holding and positioning the specimen – is the basis of light microscopes today. Why use electrons instead of light? A modern light microscope (often abbreviated to LM) has a magnifica- tion of about 1000x and enables the eye to resolve objects separated by 0.0002 mm (see box A). In the continuous struggle for better resolution, it was found that the resolving power of the microscope was not only limited by the number and quality of the lenses but also by the wavelength of the light used for illumination. It was impossible to resolve points in the object which were closer together few hundred nanometres – see box B). Using light with a short wavelength (blue or ultraviolet) gave a small improve- ment; immersing the specimen and the front of
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FEI_SEM2006_06_AllYouWanted_pb - All you wanted to know...

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