SEM

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Soybean cyst nematode and egg ---


 * SEM -** **scanning electron microscope** (**SEM**)

A type of electron microscope capable of producing high-resolution images of a sample surface. Due to the manner in which the image is created, SEM images have a characteristic three-dimensional appearance and are useful for judging the surface structure of the sample. The SEM was pioneered by Manfred von Ardenne in the 1930s. The instrument was further developed by Charles Oatley and first commercialized by Cambridge Instruments.

The SEM had a large dapth of field, which allows a large amount of the sample to be in focus at one time. The SEM also produces images of high resolution, which means that closely spaced features can be examined at a high magnification. Preparation of the samples is relatively easy since most SEMs only require the sample to be conductive.

The combination of higher magnification, larger depth of focus, greater resolution, and ease of sample observation makes the SEM one of the most heavily used instruments in research areas today.

Magnification: X 200

This is mosquito's head. The mosquito's head is mostly eye. The eyes of most insects are compound eyes, made up of many tiny lenses. Each lens sees a slightly different picture, making up a mosaic of the object it is looking at. This type of vision is very efficient at noticing very slight motions such as another insect trying to sneak up on it.



Magnification: X 500

The Black Widow is a cobweb spider. Their cobwebs are built in dark, out of the way places. The claw has three hooks, the middle one used to work the silk.

The Iowa State [|SEM web guide]
 * SEM has recently been combined with STM in an interesting way ||
 * read at [|http://www.fz-juelich.de/video/emundts/.] ||
 * Scanning Electron Microscope is filming a STM (Movie) ||
 * ( http://www.fz-juelich.de/video/emundts/film.mpg ) - Click and you can see the video of a Scanning Electron Microscope filming an STM in action! ||



The first modern scanning electron microscope

constructed by D.McMullan in the Cambridge University Engineering Laboratory in 1951.

The development of the SEM in the early 1950's brought with it new areas of study in the medical and physical sciences because it allowed examination of a great variety of specimens. As in any microscope the main objective is for magnification and focus for clarity. An optical microscope uses lenses to bend the light waves and the lenses are adjusted for focus. In the SEM, electromagnets are used to bend an electron beam which is used to produce the image on a screen. By using electomagnets an boserver can have more control in how much magnification he/she obtains. The eletron beam also provicdes greater clarity in the image produced.

Krillommatkils

What is an Electron Microscope?

The development of the Scanning Electron Microscope in the early 1950's brought with it new areas of study in the medical and physical sciences because it allowed examination of a great variety of specimens. As in any microscope the main objective is for magnification and focus for clarity. An optical microscope uses lenses to bend the light waves and the lenses are adjusted for focus. In the SEM, electromagnets are used to bend an electron beam which is used to produce the image on a screen. By using electromagnets an observer can have more control in how much magnification he/she obtains. The electron beam also provides greater clarity in the image produced.



Modern version of SEM

The SEM is designed for direct studying of the surfaces of solid objects. By scanning with an electron beam that has been generated and focused by the operation of the microscope, an image is formed in much the same way as a TV. The SEM allows a greater depth of focus than the optical microscope. For this reason the SEM can produce an image that is a good representation of the three-dimensional sample.

How does SEM work?

The SEM uses electrons instead of light to form an image. A beam of electrons is produced at the top of the microscope by heating of a metallic filament. The electron beam follows a vertical path through the column of the microscope. It makes its way through electromagnetic lenses which focus and direct the beam down towards the sample. Once it hits the sample, other electrons ( backscattered or secondary ) are ejected from the sample. Detectors collect the secondary or backscattered electrons, and convert them to a signal that is sent to a viewing screen similar to the one in an ordinary television, producing an image.