Focused ion beams have been used since the 1960s to investigate the chemical and isotopic composition of minerals. A focused ion beam blasts atoms and molecules free from the surface of a small sample of material; some of these free particles are also ions, and these are guided by electric fields to a mass spectrometer which identifies them with great precision.

An ion is an atom or molecule with a net electric charge. Electric fields subject electric charges to forces; therefore, electric fields can be used to move and steer ions. A continuous stream of ions moving together is termed an ion beam; a focused ion beam (FIB) is produced by using electric fields to guide a beam of ions.

In a typical FIB analysis, a narrow beam of argon, gallium, or oxygen ions traveling about 500,000 mph (800,000 kph) is directed at a...