In the field of transmission electron microscopy, phase-contrast imaging may be employed to image columns of individual atoms. This ability arises from the fact that the atoms in a material diffract electrons as the electrons pass through them (the relative phases of the electrons change upon transmission through the sample), causing diffraction contrast in addition to the already present contrast in the transmitted beam. Phase-contrast imaging is the highest resolution imaging technique ever developed, and can allow for resolutions of less than one angstrom (less than 0.1 nanometres). It thus enables the direct viewing of columns of atoms in a crystalline material.