Coating and Conductivity Techniques for SEM and Microanalysis

Nonconducting samples invariably need some sort of treatment before they can be examined and analyzed under optimal conditions in electron-beam instruments that rely on an emitted signal to provide information. The treatment is necessary to eliminate or reduce the electric charge that builds up rapidly in a nonconducting specimen when it is scanned by a beam of high-energy electrons. Figs. 4.63a–c and 4.64a–c show examples of pronounced and minor charging as observed in the SEM. In addition to charging phenomena, which result in image distortion, the primary beam also causes thermal and radiation damage, which can lead to a significant loss of material from the specimen. In many situations the specimen may acquire a sufficiently high charge to decelerate the primary beam, and the specimen may even ultimately act as an electron mirror (see Fig. 4.62).