Atomic force micrograph of a protein crystal on a mica substrate. The atomic force microscope (AFM) is capable of atomic-scale resolution, and works by drawing a very small probe across the surface of the sample. The vertical movement of the probe, caused by the topography of the sample, is converted into electronic signals. These are then processed to give a map of the surface as seen here. Mica is used as the substrate as it cleaves almost perfectly along its crystal layer line, giving a near-perfectly flat surface. Magnification unknown.