Transmission electron microscopy. Researcher operating a transmission electron microscope (TEM). In a TEM, a beam of electrons is propelled down through a column into a vacuum chamber containing a thin sample. After passing through the sample, the electrons hit a screen which fluoresces to give an image. The image can also be shown on a screen. TEM images have a much higher resolution and can achieve a much higher magnification than conventional optical microscopes. Photographed as part of work carried out by the UK's Health and Safety Laboratory (HSL).