The Transmission Electron Microscope (TEM), like the SEM, also uses an electron beam to obtain images.  As with the SEM, electrons are accelerated through a potential difference, but are focused by a magnetic field rather than a lense. Furthermore, the TEM takes advantage of the wave nature of electrons in order to produce images.  The electron beam is then more effective or obtains a high resolution than using a light beam because the charge of the electrons interacts with the sample.