Imaging and analysis in materials science by low vacuum scanning electron microscopy

Low vacuum scanning electron microscopes (SEMs) enable stable imaging of non-conductive samples by allowing a small pressure of gas in the specimen chamber. However, the gaseous ions that electrically stabilise the specimens can also give rise to potentially useful new contrast mechanisms. The charge stabilisation process in these instruments is summarised and recent efforts to understand the new complex, dynamic contrast mechanisms are reviewed. Several significant low vacuum and environmental SEM applications papers are critically considered, and the results evaluated in light of the imaging theory presented. Although the applications have been chosen to represent a wide range of topics of interest to materials scientists, a slight emphasis has been placed on applications relevant to the electronics industry. In particular, it should be noted that many of the dynamic contrast effects have characteristic time constants that are comparable to experimental parameters such as scan rate. The potential for using these effects to map electronic inhomogeneities and defects is discussed.