Sem

Electron Microscopes

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Figure 11.8 Resolution with various microscopes. Electron microscopes include scanning (SEM), transmission (TEM), and scanning tunneling (ST) or scanning probe (SP).

The disadvantages of TEM microscopy include the much higher cost and complexity, and the need for sophisticated preparation of samples, such as cutting thin sections of the cells to be observed. Of course, these techniques kill the cells. A main use of TEM is looking at internal cell structures.

SEM offers somewhat less magnification, with resolutions down to around 10 nm. It is based on the detection of backscattered rather than directly transmitted electrons. Typically, the specimen's surface is treated with an electron reflective coating, such as gold. As the applied electron beam is scanned back and forth across this sample, the scattered electrons provide a three-dimensional image of the coated surface. However, care must be taken that the coating procedure itself does not produce artifacts (false observations).

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