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The FIB microscope works much like the SEM in that it scans the sample with a focused beam. Instead of electrons, the FIB accelerates some ion (typically ionized gallium or some other liquid metal). Unlike the SEM, the FIB's beam is destructive, in that it can peel layers of atoms from the sample each time it scans.

This can be useful in a number of ways. For instance:

  • It can clean the surface of the sample, removing the impure surface and exposing the underlying layers.
  • It can slowly etch away at the sample, showing progressive cross sections until nothing is left.
  • If the power is turned up, and the scanning area shaped, it can actually mill the sample, creating a shaped hole. Most FIB's have a sample platform with multiple degrees of freedom, so that after milling a nice deep rectangular hole in your sample, you can tilt the platform and look at the newly exposed surface on the side of the hole.
  • The FIB can be used in nano-fabrication, both by carving precise holes and by depositing impurities on or injecting impurities into a sample. In addition to milling, FIB methods have been used to etch and sputter.
These methods can be used on semiconductors to do failure analysis, repair, and initial fabrication. In the laboratory, these methods are used to examine the structure of the samples. I have seen a wide variety of samples put into the FIB, examining everything from cellular content of fossils to crystal structure of metals.

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