Scanning transmission electron microscope advantages

XAS requires synchrotron radiation and a relatively large amount of material but no vacuum condition. On the other hand, EELS can be performed directly using an electron spectrometer fitted to a scanning transmission electron microscope (STEM). Here, the main advantage is the high spatial resolution attainable. (The incident electron beam can be as. small as I nm in diameter.) EELS can also be coupled with conventional transmission electron microscope (TEM) facilities and particularly high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS). 

Resolution in the STEM is limited by the probe diameter, which is about 1 nm in equipment dedicated to this operating mode, at the cost of using a cold field emission gun requiring an ultravacuum. Because of the high-precision optics and the point-by-point image formation principle, the STEM combines the advantages of scanning electron microscope analysis with resolution performance levels similar to the transmission electron microscope. 

Scanning transmission electron microscopy gives essentially the same type of results and has the same type of difficulties as the conventional TEM. There are two types of instruments, the dedicated STEMs, which generally have a UHV column, and the TEM based instruments mostly known as AEMs (analytical electron microscopes). A detailed comparison of STEM and TEM was given in Section 2.4.1.3. There are some advantages in using the STEM on polymer samples in particular it seems that thicker samples can be used. However, the added complexity and cost, combined with lower resolution in the AEM STEM mode, make it unlikely that either kind of instrument would be purchased for polymer studies. 

The electron microprobe has been used by LeRoux et al. [1970] in the study of chemical composition of various parts of sand-size weathered micas. The scanning electron microscope is probably the most useful instrument in the study of the micromorphology of micas. Its great depth of field is a distinct advantage over the transmission electron microscope. 

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