scanning tunneling microscope (STM), device for studying and imaging individual atoms on the surfaces of materials. The instrument was invented in the early 1980s by Gerd Binnig and Heinrich Rohrer, who were awarded the 1986 Nobel prize in physics for their work. The underlying principle of the STM is the tunneling of electrons between the sharp tip of a probe and the surface of the sample under study. The flow of electrons is extremely sensitive to the distance between the tip and the sample. As the tip is swept over the surface the height of the tip is continually adjusted so as to keep the flow of electrons constant. A map of the “bumps” on the surface is then obtained by accurately recording the height fluctuations of the tip. The STM was used in 2004 to measure the charges of individual atoms, and in 2010 researchers used a modified STM to observe the magnetism, or spin, of atoms on the nanosecond timescale.
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