Scanning tunnelling micrograph of gold atoms on a graphite substrate. The gold atoms, shown as yellow, red and brown, have formed an aggregate of 1x1. The graphite (carbon) atoms are shown as green. The scanning tunnelling microscope (STM) uses a fine point electrode, a few atoms thick at the tip. This is brought to within a few angstroms of the sample's surface. As the electron clouds of the tip and the sample atoms interact, a small 'tunnelling' current passes. The electrode scans across the surface, moving vertically to maintain the tunnelling current. This motion is then processed to produce a map such as this.
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