A new class of SEM has evolved over the past few years which provides some startling capabilities never before available to electron microscopists. These instruments, typically referred to as environmental SEMs or variable pressure SEMs. have opened up a host of new applications that are difficult or impossible with a standard SEM. Many of the constraints of sample preparation and handling that exist with a conventional SEM do not apply to environmental SEMs.

An environmental SEM functions like a conventional SEM except that you can introduce air or any other gas into the chamber and raise the chamber pressure above the normal high vacuum range of 10-5 or 10-6 Torr. Inmost instruments the vacuum can be raised to as much as 1 Torr. This represents a 6 order of magnitude increase in chamber pressure. Environmental SEMs can achieve this high chamber pressure without damage to the electron source by using differential pumping apertures in the column.