Electron microscopes produce an image of a specimen by using a beam of electrons rather than a beam of light. As electrons have shorter wavelength than visible light, electron microscopes to produce higher-resolution images.
They are discovered to visualize the ultra-structure of microorganisms. It has magnitude of 10,000x or more. They can be used to visualize the subcellular structures of the cells. However, live cells cannot be visualized by electron microscopes as specimens are prepared through specialized fixation process which leads to cell death.
In scanning electron microscopy (SEM), a beam of electrons moves back and forth across surface of a cell or tissue, creating a detailed image of 3D surface. Electron beam scans the surface of specimen which leads to release of secondary electrons and other types of radiation. SEMs are used in forensic laboratories to analyze a wide variety of samples, including paint, particles, fractures, toolmarks, and gunshot residue.
In transmission electron microscopy (TEM), sample is cut into extremely thin slices before imaging, and electron beam passes through the very thinly sectioned slice and projects the beam onto a specially treated plate that transmits the image to a monitor. TEM is often used to obtain detailed images of the internal structures of cells.