ABSTRACT
Within the wide variety of techniques for characterising the microstructure of materials, some operate using a relatively simple environment such as the normal atmosphere whereas others require sophisticated containment systems usually to produce extremely good vacuums. For example, simple electron microscopes operate with a vacuum that is less than 102 Pa and, indeed, with the addition of sophisticated analytical attachments such as windowless spectrometers there is now a trend to achieve pressures of 105 Pa or better. Any technique that is required to analyse a surface either chemically or crystallographically is compelled to operate with vacuums in the region 107 to 109 Pa. Figure 3.1 indicates some of the techniques that are currently available for microstructural evaluation and their vacuum requirements. Since so many methods of characterising material microstructure require the production of high and ultra-high vacuums (UHV) we will describe the various methods for producing, containing and measuring vacuums (O’Hanlon (1989), Leybold (1987)).
