Scanning Tunneling Microscope
The Scanning Tunneling Microscope was the first born in the SPM family. When two electrodes are brought very close together (~nm) and they have a potential difference Vb, there is a fair probability that some electrons will tunnel across the electrodes gap. The STM uses the tunneling current exiting between these electrodes as the interaction that can render the surface topographies of a particular specimen.
When a constant current and a control system are put in place, the probe raster the sample and describe it's topography as illustrated in the figure below.
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| Operation principle of the STM: A tip scans the surfaces at a constant current It. A change in the surface topography produces a proportional change in the scanning height called lateral resolution (\delta). |
The scientific background section describes thoroughly the behavior and physics behind the STM