Physical basics of scanning electron microscopy in volume electron microscopy

Volume electron microscopy (vEM) has become a widely adopted technique for acquiring three-dimensional structural information of biological specimens. In addition to the traditional use of transmission electron microscopy, recent advances in the resolution of scanning electron microscopy (SEM) made it suitable for vEM application. Currently, various types of SEM with different advantages have been utilized. For selecting the appropriate type of SEM to obtain optimal vEM images for the purpose of individual research, it is important to understand the physics underlying each SEM technology. This article aims to explain the physics for signal electron generation, various objective lens configurations and detection systems, employed in SEM to enhance high-resolution imaging and improve signal detection conditions.