In scanning electron microscopy (SEM) the interaction of an electron beam with a material results in a large number of externally observable signals. a) Describe the difference between secondary electrons (SE) and backscattered electrons (BSE). Explain the origin of these signals and the typical information obtained from their analysis. b) Explain the meaning of the term " Z-contrasf' when detecting backscattered electrons. c) Sample charging can result in poor imaging and artefacts during analysis of non-conducting specimens. Describe the mechanisms of two techniques that can be used to reduce sample charging charge limitation and describe the mechanism by which they reduce charging