Scanning electron microscopy, Biology

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Scanning Electron Microscopy (SEM)

While 'TEM is useful to study the internal structul-c of thc ccll. SEM is an important technique if you wish to examine the surl'ace features of the specimen. Moreover, a specimen can be viewed at different angles. The resolving power of a SEM is lower than that of a TEM since a resolution of only about 3.0 nm can be attained hy SEM.

In a SEM, a low energy beam of electrons (primary electrons) strikes the surface of a specimen. This causes the emission of the secondar!, electrons from the specimen which are gathered by a photonlultiplier tube to form an image which is built up line by line as in the case of television. The image forlncci by SEM has a three-dimensional appearance. Unlike -in a TEM, the electrons in a SEM do not pass through the specimen.


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