Unlike Scanning Electron Microscopy that bounces electrons off the surface of a sample to produce an image, Transmission Electron Microscopes (TEMs) shoot the electrons completely through the sample.
How TEMs Work
TEMs work by using a tungsten filament to produce an electron beam in a vacuum chamber. The emitted electrons are accelerated through an electromagnetic field that also narrowly focuses the beam. The beam is then passed through the sample material. The specially prepared sample is a very thin (less than 100nm) slice of material. The electrons that pass through the sample hit a phosphor screen, CCD or film and produce an image. Where the sample has less density, more electrons get through and the image is brighter. A darker image is produced in areas where the sample is more dense and therefore less electrons pass through.
TEMs can produce images with resolution down to 0.2nm. This resolution is smaller than the size of most atoms and therefore images can be produced using TEM that show the true structural arrangement of atoms in the sample material.