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Uncharted atomic landscapes

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1:46pm, August 14, 2007

Electron microscopes can now not only image single atoms but also map the locations of different chemical elements in a sample.

A scanning-transmission electron microscope (STEM) operates by sending an atom-thin beam of electrons through a sample. Those electrons lose energy as they kick up the energy of some of the sample's electrons. The energy losses depend on the characteristic energies of electron states in an atom. Exploiting that fact, scientists have in recent years learned to identify which elements the beam has encountered.

So far, however, researchers haven't been able to determine the locations of those elements on the two-dimensional image that the microscope produces. That's because the STEM detector varies somewhat in sensitivity across its area, and because it's hard to keep a sample still.

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