TEM In transmission electron microscopy (TEM) an electron beam passes through a very thin sample of material and an image is formed by detecting the electrons that emerge from the other side. The electrons are transmitted or diffracted to various extents depending on the angle between the incident electron beam and the various crystal planes within the material. This effect provides contrast between grains of varying orientations and, in particular, highlights crystal defects in the material. By tilting the specimen, or moving apetures, images can be produced containing only electrons diffracted by particular crystal planes. These images assist determination of crystal structure and orientation. Modern high resolution TEMs can achieve spatial resolutions better than 0.1 nm.