The document describes the transmission electron microscope (TEM). It begins by stating that TEM can be used to examine samples as small as 0.2nm, smaller than what a scanning electron microscope can view. The principle of TEM is that electrons are transmitted through a specimen and the image is formed based on the transmitted or diffracted electrons. Key components include the electron gun, magnetic lenses, and fluorescent screen. TEM works by firing electrons through a specimen using lenses, with transmitted electrons forming an image and diffracted electrons eliminated to increase contrast. TEM provides high resolution imaging down to the atomic scale and is used in nanoscience and viewing internal structures of cells and viruses.