is microscope started its journey as an instrument that done away with limited resolving power of optical microscopes and has evolved considerably over years to become an instrument of versatile capabilities. Today, an SEM has become an indispensible instrument for any R&D or production set up dealing with advanced materials science. In the subsequent sections interaction of electrons with matter, basic principles of electron microscopy, architecture and working of scanning electron microscope, different attachments to an SEM and applications of SEM in materials science will be discussed in brief with special emphasis on specifications of a modern SEM.
Electrons as a probe are extremely versatile as they generate a wide range of signals which can be detected and processed to get useful and meaningful insight about surface topography, microstructure, microchemistry and micro-texture of the material being probed. Different kinds of signal generated as a result of interaction of electron probe are shown in Fig. 1 .
When thickness of the specimen is less than ~ 100 nm only then the incident electron beam is able be pass through it and generate different kind of transmitted signals. However, the transmitted signals are relevant for Transmission Electron Microscope (TEM) and not for Scanning Electron Microscope (SEM); therefore, we will not discuss about transmitted signals here. Among the reflected signals secondary electrons (SE) and Back Scattered Electrons (BSE) are relevant for SEM for imaging and characteristic X-rays are useful for chemical analysis in SEM. Besides, BSE is also useful in micro-texture analysis using Electron Back Scattered Diffraction (EBSD) attachment. Therefore, we will limit our focus to these signals only.
When electron beam strikes the specimen, it knocks out the inner shell electrons and the vacancy thus created is immediately filled by an electron from higher shells. This electronic transition leads to generation of X-rays which are ...Show more