PHILIPPE PLAILLY / SCIENCE PHOTO LIBRARY PHILIPPE PLAILLY / SCIENCE PHOTO LIBRARY
Scanning tunnelling micrograph of palladium atoms on a graphite substrate. The palladium atoms, shown as white, form a hexagonal arrangement with a spacing of 0. The graphite (carbon) atoms are shown as blue. 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 that seen here.
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