Scanning Electron Microscopy SEM/EDX is an extremely high magnification microscope which provides images and elemental analysis top down or in cross-section. 

Field Emission Scanning Electron Microscopy (FESEM)
Environmental Scanning Electron Microscopy (ESEM)

Field Emission Scanning Electron Microscopy (FESEM)

Scanning Electron Microscopy (SEM) is the best known and most widely-used of the surface analytical techniques. High resolution images of surface topography, with excellent depth of field are produced using a highly-focused, scanning (primary) electron beam. The primary electrons enter a surface with an energy of 0.5 - 30 keV, and generate many low energy secondary electrons. The intensity of these secondary electrons is largely governed by the surface topography of the sample. An image of the sample surface can thus be constructed by measuring secondary electron intensity as a function of the position of the scanning primary electron beam. High spatial resolution is possible because the primary electron beam can be focused to a very small spot (<10 nm). High sensitivity to topographic features on the outermost surface (<5 nm) is achieved when using a primary electron beam with an energy of <1 keV.

In addition to low energy secondary electrons, backscattered electrons and X-rays are also generated by primary electron bombardment. The intensity of backscattered electrons can be correlated to the atomic number of the element within the sampling volume. Hence, some qualitative elemental information can be obtained. The analysis of characteristic X-rays emitted from the sample gives more quantitative elemental information. Such X-ray analysis can be confined to analytical volumes as small as 1 cubic micron.

SEM, accompanied by X-ray analysis, is considered a relatively rapid, inexpensive, and basically non-destructive approach to surface analysis. It is often used to survey surface analytical problems before proceeding to techniques that are more surface-sensitive and specialized. The complete analysis time of a sample can vary greatly, depending on the complexity of the analysis required. Typically, a study of a sample surface, including several micrographs and EDX analysis, would take about one hour.

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Environmental Scanning Electron Microscopy (ESEM)

In a typical ESEM, pressure-limiting apertures with differential pumping are installed before the electron detector, so that analysis can be performed in a low vacuum regime (1-50 Torr, ca. <10^-7Torr in normal SEM).  As such, samples which are not vacuum stable and cannot be examined using conventional SEM or FESEM, can be studied with ESEM.  ESEM is thus a very useful tool to image biological samples, pharmaceutical, food and non-metallic samples (e.g. plastics and elastomers).

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