Scanning tunnelling microscope (STM) image of a high purity gold surface. At this magnification, the metal displays a characteristic rolling hills" structure. The hills are considerably smaller than the metallic grain size and may indicate an attempt at minimizing surface energy when the metal was cooling from its molten state. Scanning tunnelling microscopy is based on quantum mechanical effects, recording the surface structure of a substance at the level of the individual atoms. Magnification: x250,000 at 35mm size. Image size: 1000 x 500 Angstrom Units."