Advantages
The presence of gas around a specimen creates new possibilities unique to ESEM: (a) Hydrated specimens can be examined since any pressure greater than 609 Pa allows water to be maintained in its liquid phase for temperatures above 0 °C, in contrast to the SEM where specimens are desiccated by the vacuum condition. (b) Electrically non-conductive specimens do not require the preparation techniques used in SEM to render the surface conductive, such as the deposition of a thin gold or carbon coating, or other treatments, techniques which also require vacuum in the process. Insulating specimens charge up by the electron beam making imaging problematic or even impossible. (c) The gas itself is used as a detection medium producing novel imaging possibilities, as opposed to vacuum SEM detectors. (d) Plain plastic scintillating BSE detectors can operate uncoated without charging. Hence, these detectors produce the highest possible signal-to-noise-ratio at the lowest possible accelerating voltage, because the BSE do not dissipate any energy in an aluminium coating used for the vacuum SEM.
As a result, specimens can be examined faster and more easily, avoiding complex and time consuming preparation methods, without modifying the natural surface or creating artifacts by the preceding preparation work, or the vacuum of the SEM. Gas/liquid/solid interactions can be studied dynamically in situ and in real time, or recorded for post processing. Temperature variations from subzero to above 1000 °C and various ancillary devices for specimen micro-manipulation have become a new reality. Biological specimens can be maintained fresh and live. Therefore, ESEM constitutes a radical breakthrough from conventional electron microscopy, where the vacuum condition precluded the advantages of electron beam imaging becoming universal.
Read more about this topic: Environmental Scanning Electron Microscope
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