Abstract Modern-day electron-beam instruments for the analyses of solid materials are available in a wide variety of forms with an almost bewildering range of capabilities. The capabilities chosen for an electron-beam instrument in a particular laboratory will depend on the common applications or the predilection of the primary users. In addition, specific electron-beam instruments may be optimized for certain applications depending on the nature of the electron-solid interaction to be analyzed. For example, instruments dedicated to precise (i.e., <1 % relative error) elemental analyses of solids using secondary X-rays, termed electron microprobes, are often of limited utility for collecting structural or diffraction data, although electron channeling patterns can be obtained from some instrument configurations. On the other hand, spatially precise (i.e., <3 Å) structural data can be routinely obtained from electron-transparent solids in modern-day analytical electron microscopes by monitoring phase changes produced in transmitted electrons as they pass through oriented crystalline materials. The electron-beam instruments currently available can be understood in terms of two basic types: the scanning electron microscope (SEM) and the transmission electron microscope (TEM). All other instruments and their operating modes are essentially variations on or combinations of these two basic types of instruments, with appropriate signal detectors. Table 1 lists four common electron-beam instruments and basic analytical properties, such as precisian of chemical analyses, spatial resolution, and type of probe. The analytical properties are approximate limits only and assume ideal operating conditions (e.g., optimum samples and sample preparation procedures). These instruments operate in either a rastered or

Abstract The versatility of a modern-day analytical electron microscope (AEM) can be considerably enhanced over that presented in previous chapters of this volume by the addition of temperature-controlled specimen stages and/or environmental cells. In some cases, (e.g., for a liquid nitrogen (LN2) cold stage), a modest financial investment may reduce inherent problems of contamination and radiation damage during the examination of difficult materials, such as clays or zeolites. Indeed, for the study of certain polymers and the precise determination of mineral chemistry, the use of LN2 cold stages appears to be the method of choice. Literature reports on specific applications to clay mineral analyses are not common, but on the basis of a few successful investigations, it is apparent that wider application of these techniques will prove invaluable to clay mineralogists. In this chapter, some fundamental aspects of electron analyses using the relatively high beam current densi ties of modern AEMs will be examined. These aspects are developed in terms of thin-film elemental data, in which the analyst typically uses a 200-400 A diameter electron beam. For the beam current densities inherent in this type of analysis, contamination, etching, and radiation damage can significantly hinder the precise determination of elemental compositions of individual clay minerals. Similar arguments regarding contamination and element loss may apply, although to a lesser extent, to samples imaged in the high-resolution (phase-contrast) mode, due to the requirement of high illumination and short exposure times. In this chapter, the use of LN2 cold stages in the scanning