Abstract
The environmental scanning electron microscope (ESEM) utilises a secondary electron detector capable of operating at pressures in the range of 1 ~ 20 Torr (130 ~ 2700 Pascals). By use of differential pumping apertures the electron gun and column can be maintained at "normal" vacuum levels of 10-5 Torr. A pressure of 10-2 Torr exists within the secondary electron detector separated from the specimen chamber by another differential pumping aperture. The specimen chamber pressure is produced by admitting a gas to the chamber under operator control. The gas can be any ionisable gas. Water vapour is a commonly used chamber gas. By controlling chamber gas pressure and sample temperature, by means of a Peltier effect stage, condensation and evaporation can be produced. The ability to maintain samples in a fully hydrated state in this way singles out the Electroscan ® ESEM as a unique instrument. ESEM presents an opportunity to examine biological samples with their natural water content present.
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