need to know everything about electron microscopy,......

[Triena]

...more in focus about scanning electron microscopy.? Hey friends, i have a workshop to attend on Scanning electron microscopy. I am a microbiology graduate. I dont know much in detail about electron microscopy. please tell me where can i read about it. i am looking for answers like how it works, the principle n mechanism, also what are the specimens it is used for. I know i m gonna get u something fruitful so, thanks in advance !
i was reading something and i think that the specimen should first go through some pretretaments,.... let me know all about it ...

[Geoffrey B]

There are two types, Transmission Electron Microscopes (TEM) and Scanning Electron Microscopes (SEM).

The basic principle for both is to use focused electron beams that travel through a specimen and give an image on the other side that reflects electron density. The image is interpreted by a computer and displayed on a monitor. The stains used are usually heavy metals, like osmium, to better reflect electrons (I'm hazy on the exact physics behind it, that's the best I can offer).

TEM is able to reach the greatest magnifications, up to 500,000X or even more. The samples used must be extremely thin, on the order of 20 or so nanometers, and this is sort of a limitation. TEM can offer great images of slices through cells, and are able to distinguish fine features such as cilia, organelles, and even plasma membranes and individual proteins (if they are large enough).

SEM is a bit different. It can only go to around 100,000-200,000X magnification, but a sample of any thickness can be used. It offers a great image of the surface of the sample. So if you want to see the outer surface of a cell, and all its microvilli, cilia, or to get a feel for its overall shape, SEM is the way to go. They can be very beautiful images.

Oh, I should add that the samples for SEM are usually coated in a metal like gold or palladium, instead of dyed, and in both TEM and SEM a vacuum pump is used to remove as much air as possible, so the electrons can move freely to the samples. The electron source is usually a tungsten filament, not unlike the kind used in light bulbs.