The environmental SEM is an extremely adaptive instrument, allowing a range of materials to be examined under a wide variety of conditions. The limitations of the instrument lie mainly with the restrictions imposed by the need to maintain a moderate vacuum around the electron gun. The primary effect of this has been, in a practical sense, the limited low magnification available. Recently this has been overcome by modifications to the final pressure limiting aperture and secondary electron detector (Fig.l). The modifications are simple and users should be brave in this regard.

A variety of electron detectors now exist including various secondary, backscattered and cathodoluminescence systems (Figs 2-5). These provide an excellent range of options; the ESEM must be regarded as a conventional SEM in that a range of imaging options should be installed. In some cases, e.g. cathodoluminescence, the lack of coating provides an advantage unique to the low vacuum SEMs.