Scanning Tunneling Microscopy (STM)
Scanning-tunneling microscopy (STM) can image surfaces of conducting materials with atomic-scale resolution. It uses an atomically-sharp metal tip that is brought very close to the surface. When the tip and sample are connected with a voltage source, a small tunneling current flows between the tip and sample surface. This current can be measured, and the magnitude depends on the distance between the tip and the surface. As the tip is moved laterally across the surface, a feedback mechanism moves the tip up and down to maintain a constant tunneling current. Rastering the tip across the surface therefore produces a topographic map of the surface. See also the related technique of atomic-force microscopy.
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