TEM passes an electron beam through a thinly-sliced sample to create a two-dimensional image of the sample. Heavier atoms block the electron beam more than light elements which creates contrast in the image. Samples are prepared by embedding the sample in a resin and sectioning slices of the sample that are thin enough for the electron beam to pass through. Skill is required to create sample sections of appropriate quality for viewing. If crystalline materials are analyzed by TEM, electron diffraction patterns can be collected that can be used to determine lattice spacing in the crystal structure which can help identify an unknown material.
Transmission Electron Microscopy (TEM) is the most powerful microscope available and can achieve magnifications of 1,000,000X or more. TEM generates high resolution, two-dimensional, black and white images. TEM uses the same basic principles as optical microscopy. In TEM, electrons are employed instead of light; electromagnetic lenses replace glass lenses; and images are viewed on a screen instead of through an eyepiece. The sample is sliced thin enough for electrons to pass through. The prepared sample is placed in a vacuum chamber. Electrons are passed through several electromagnetic lenses, pass through the sample and make contact with a screen, where it is converted into an image. Light areas of the image indicate more electrons have passed through the sample. Detail and quality of the image can be improved by using higher speed electrons. High speed electrons correlates to shorter wavelength; shorter wavelength results in better quality images.